Single crystal CVD diamond membranes as Position

Sensitive X-ray Detector K. Desjardins, a,1 C. Menneglier a and M. Pomorski b a Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin BP 48, Gif-sur-Yvette, 91190, France b CEA-LIST, Diamond Sensors Laboratory, 91191, Gif-sur-Yvette, France E-mail: kewin.desjardins@synchrotron-soleil.fr

A

: Transparent X-ray Beam Position Monitor (XBPM) has been specifically developed for low energy X-ray beamlines (1.4 keV < E < 5 keV) allowing to transmit more than 80% of 2 keV energy beam. The detector is based on a free-standing single crystal CVD diamond membrane of 4 µm thickness with position-sensitive DLC (Diamond-Like Carbon) resistive electrodes in duolateral configuration. The measured X-ray beam induced current (XBIC) due to the interaction of X-rays with diamond membrane allows precise monitoring of the absolute beam flux and the beam position (by the reconstruction of its center-of-gravity) at beam transmissions reaching 95%. This detector has been installed at SOLEIL synchrotron on the SIRIUS beamline monochromator output and it has shown charge collection efficiency (CCE) reaching 100% with no lag-effects and excellent beam intensity sensitivity monitoring. X-ray beam mapping of the detector showed an XBIC response inhomogeneity of less than 10% across the membrane, corresponding mainly to the measured variation of the diamond plate thickness. The measured beam position resolution is at sub-micron level depending on the beam flux and the readout electronics bandwidth.

K

: Beam-line instrumentation (beam position and profile monitors; beam-intensity monitors; bunch length monitors); Instrumentation for synchrotron radiation accelerators; Detector design and construction technologies and materials 1Corresponding author.

Introduction

Many beamlines at modern light-source facilities are working with X-ray beams focused down to a few tenths of a micron, and record X-ray data within a millisecond speed. Such beamlines need fast diagnostics to precisely regulate the position of X-ray beam, where the beam stability is crucial for the success of experiments. In order to improve the performance of current beam diagnostics systems, Detector group of SOLEIL synchrotron and Diamond Sensors Laboratory (LCD) of CEA-LIST started in 2012 development of XBPMs based on single crystal chemical vapor deposited (scCVD) diamond [START_REF] Desjardins | Characterisation of CVD Diamond devices as XBPMs at SOLEIL[END_REF]. A standardized production of 40-micrometer thick resistive electrode duo-lateral diamond Position-Sensitive Detectors (PSD) has been elaborated recently. This is a unique solution on the market allows in-beam detectors with only carbon material in the direct beam. More than ten sensors are already installed and operational at SOLEIL's beam lines. A routine performance of these compact transparent in-beam scCVD diamond PSDs includes submicron position resolution and absolute beam intensity monitoring, with a minimum beam distortion and a transmittance reaching > 95%, which is state-of-the-art. Following the success of 40-micron thick scCVD diamond PSDs, our effort focused at fabrication of diamond XBPMs based on < 5 micrometers scCVD diamond membranes [START_REF] Desjardins | Ultra-thin optical grade scCVD Diamond as X-ray Beam Position Monitor[END_REF] in order to allow precise beam monitoring for lower energy Xray beamlines (E < 5 keV). An argon/oxygen plasma dry deep-etching technique developed at Diamond Sensors Laboratory of CEA-LIST was used to produce free-standing, large-area 3-micron thick scCVD diamond membranes. Those were used for XBPMs fabrication and later installed at Soleil's SIRIUS beamline for characterization purposes [START_REF] Ciatto | SIRIUS: A new beamline for in situ X-ray diffraction and spectroscopy studies of advanced materials and nanostructures at the SOLEIL Synchrotron[END_REF]. These detectors demonstrated: a precise measurement of beam intensity, a relatively good homogeneity and submicron position resolution capability depending on the beam flux and acquisition bandwidth. In the following, we present the performances of this super-thin diamond PSD.

Experimental setup

A super thin diamond XBPM has been made from a "standard grade" element six ltd. scCVD diamond slab with lateral dimensions of 4.5 mm × 4.5 mm and 300 µm thickness [www.e6.com]. This sample was laser sliced and polished to 40 µm thick plate by ALMAX easyLab [http://www.almaxeasylab.com]. According to producer, the so called "standard grade" diamond has a substitutional nitrogen content of < 1 ppm, which reduces significantly life time of the charge carriers making this material useless for thick (∼ 40 microns). XBPMs use it, however the cost is significantly reduced (×10) compared to so called "electronic grade" diamond with nitrogen content of < 1 ppb. The structural quality of diamond plate supplied has been checked by crossed-polarizer optical microscopy. The excellent structural quality is evidenced for a standard grade samples with almost perfect large area with no strain visible (figure 1.b) which has been compared to the highly birefringent electronic grade diamond plate with high concentration of structural defect (dislocations, inclusions) density giving rise to strained bulk regions, and clearly visible as bright traces in figure 1.a. The sample thickness homogeneity and quality of surfaces polishing have been characterized by an IR-FT technique at the SMIS beamline optical characterization laboratory of SOLEIL. The thickness of 38.1 µm in average has been measured (figure 2) with variation less than 0.7 µm (peak-to-peak) and microscopic roughness of 130 nm rms over the 4 mm 2 surface. Similar characteristics were measured for several diamond samples and currently these specifications are guaranteed by the ALMAX easyLab for each fabricated plate.

A method of membrane fabrication was described elsewhere [START_REF] Pomorski | Super-thin single crystal membrane radiation detectors[END_REF]. In short: using an argon/oxygen plasma deep-etching technique, a free-standing auto supported membrane is produced in the central area of the diamond slab surrounded by a thicker frame. Thickness typically ranges from 1 micron to several microns, with macroscopic lateral dimensions comparable to diamond sample size typically ∼ 3 × 3 mm. The structure and dimensions of the scCVD diamond membrane used in this work is depicted in figure 3 (left).

After hot acid cleaning, a ∼ 100 kOhm/square resistive layer of Diamond Like Carbon (DLC) (thickness of ∼ 200 nm) has been deposited on both diamond surfaces by a PVD sputtering apparatus using simple shadow masks. Finally, two pairs of lateral strip electrodes (Ti/Au) at the extremities Such prepared diamond membrane PSD is mounted and wire-bonded onto a specially designed ceramic and installed in a vacuum chamber on SIRIUS beamline at SOLEIL for characterization purposes.

The XBIC signals from four Ti/Au lateral electrodes are connected to a four-channel currentto-voltage amplifier (LOCuM-4, by ENZ www.enz-de.de) and the output of LOCuM-4 voltages are digitized by an ADC (Adlink 2010). The detector bias voltage was supplied directly from the LOCUM as depicted in figure 4.

The position of the X-ray beam is reconstructed in the two dimensions by a simple center-ofgravity algorithm:

X = K x × I x1 -I x2 I x1 + I x2 , Y = K y × I y1 -I y2 I y1 + I y2 , (2.1)
where X and Y are coordinates of the position of X-ray beam center, K x & K y are the scale factor equal to L/2 with L the distance between collecting electrodes and I (x 1,2 or y 1,2 ) is the signal collected, respectively, from horizontal (X) and vertical (Y ) electrode pairs.

Experimental results

XBIC and Charge Collection Efficiency (CCE)

The PSD diamond was irradiated with synchrotron X-rays on the SIRIUS beamline (E = 4 keV, Flux ∼ 10 13 ph/s), and the sum of XBICs of each pair of lateral electrodes was measured as a function of the detector bias voltage. Results are shown in figure 5. Despite the rather high concentration of the nitrogen impurity, giving rise to a deep 1.7 eV (below conduction band) trapping center, present in the standard grade ElementSix diamond, a full CCE was evidenced for only 2 V/µm for the detector active area consisting of 4 microns thick membrane. A quick saturation of XBIC signal is reached due to the extremely short < 40 ps charge carriers transit time in such a thin layer, which anyhow is significantly shorter than the nitrogen altered lifetime of charge carriers.

The measured total induced XBIC of It = 63 µA is in excellent accordance with the expected current and it is given as:

It = q × E ph ε p × A E ph × Φ, (3.1)
where q is the value of the electron charge, E ph is the incident-beam energy and ε p = 13.25 ± 0.5 eV is the average electron-hole pair creation energy for X-ray absorption in diamond, A is the absorption factor depending on the energy E ph and diamond thickness, Φ is the X-ray beam flux. Thus, the complete CCE of the sensor allows absolute monitoring of X-ray beam flux during the experiment with a high precision (figure 6). Additionally, we do not observe any persisting currents or lageffects frequently reported for defective pcCVD XBPMs. The figure 7 shows the perfect time response of the scCVD membrane PSD XBIC generated during the beamline shutter opening.

The homogeneity of the XBIC response

The XBIC spatial homogeneity of the PSD was determined by a 2D scan of an X-ray beam spot of 200 µm × 200 µm size over the detector active area. The 2D map of XBIC image in figure 8 shows the total intensity inducted for all scanning positions of the beam on the PSD. For the 1 mm 2 center of the active area, we measured a variation of only 20 nA rms corresponding to 1.2% a fluctuation. The XBIC spatial fluctuation correlates with the variation in the thickness of the diamond plate observed before the etching process (figure 2), thus this variation is mainly related to X-ray beam absorption. Spatial inhomogeneity does not alter significantly the position monitoring if only small beam spots are used, however for better performance or precise beam intensity monitoring of moving beams the XBIC must be corrected for the sample thickness variation (by calibration) or thickness homogeneity must be improved for future devices.

X-ray Beam Position reconstruction and linearity

The scale factor in horizontal and vertical directions (K x & K y in equation (2.1)) have been checked by recording the PSD currents versus beam position (figure 9) and by fitting the difference over the sum versus beam position with a linear function. The scale factor is in accordance with the inter-electrode dimensions (L x = 2.7 mm & L y = 3.5 mm) with K x = 1.3 mm and K y = 1.9 mm.

Figure 10 illustrates the very good agreement of X-ray beam reconstructed position with real position of thin PSD after the K x , K y factors calibration.

X-ray Beam Position resolution capability

The position resolution depends on the incident beam flux (intensity of XBIC), and the bandwidth of the readout electronics. A complete study of this dependence, based on experimental measurements compared to the theoretical model, is under study. For these particular experimental conditions the position resolution capability of the diamond PSD detector is illustrated in the figure 11. The detector was displaced by 10 microns using stepper motors (curve in blue), the X-ray beam reconstructed position for an ADC integration time of 100 ms and a X-ray beam flux of 10 13 ph/s (XBIC of 63 µA) is displayed in red. As presented, the relative X-ray beam movement is perfectly reconstructed by the PSD with a standard deviation of about 130 nm rms for these conditions.

Conclusion

We have fabricated and demonstrated the performances of a scCVD diamond membrane PSD intended for in-beam monitoring of the tender X-ray beamlines. The excellent charge collection efficiency, the relatively good homogeneity for the XBIC response and submicron beam position resolution were demonstrated at less than 4% absorption of the incident X-ray beam at 4 keV. Two ready-to-use detectors have been prepared for SIRIUS beamline. More sensors are planned for SIRIUS and METROLOGIE beamlines but the thinning process remains a key issue in the production of these membranes. Due to the presence of structural defects within the diamond bulk and despite the screening procedure the yield of pinholes free membranes fabrication is rather far from 100%.

Figure 1 .

 1 Figure 1. Crossed-polarizer optical microscopy images obtained for two ElementSix sc-CVD diamond plates: (a) electronic grade, (b) low-birefringence standard grade.

Figure 2 .

 2 Figure 2. A thickness cartography obtained by an FT-IR microscope on laser sliced and re-polished 40 micron thick scCVD diamond plate before deep plasma etching to the membrane.

Figure 3 .

 3 Figure 3. A cross-sectional schematic view of free-standing scCVD diamond membrane PSD with its dimensions (in blue -diamond membrane, in black -DLC resistive layers, in green -four lateral electrodes made of Ti/Au. A photograph of fabricated scCVD diamond PSD ready-to-mount on the dedicated readout pcb.

Figure 4 .

 4 Figure 4. Diagram of the scCVD diamond membrane duo lateral PSD and signal generation principles.

Figure 5 .

 5 Figure 5. XBICs vs. detector bias for the 4 µm thick scCVD diamond membrane PSD.

Figure 6 .Figure 7 .

 67 Figure 6. Total current time scan. Signal to noise ratio better than 0.1% (ADC sampling 100 Hz)

Figure 8 .

 8 Figure 8. Full-area 2D homogeneity map of total XBIC (left) and in 2 × 2 mm of the center of active area (right)

Figure 9 .

 9 Figure 9. Cross-over response of the diamond membrane PSD while scanning the beam through the detector in horizontal direction (I x1 , I x2 ).

Figure 10 .

 10 Figure 10. Reconstructed beam position vs. beam position coordinates obtained from X step motor with the scale factor determined.

Figure 11 .

 11 Figure 11. Time scan of the X-ray beam with a 10 microns displacement of the scCVD diamond membrane PSD for an ADC integration of 100 ms. In blue -PSD motor displacement, in red -PSD reconstructed position.

Acknowledgments

We would like to thanks the SIRIUS beamline teams for their support and beam-time necessary for the characterization of the very thin PSD XBPM.


Nouha Ben Hafaiedh

Florence Fourcade

Nizar Bellakhal

Abdeltif Amrane
email: abdeltif.amrane@univ-rennes1.fr

Iron oxide nanoparticles as heterogeneous electro-Fenton catalysts for the removal of AR18 azo-dye

Keywords: Iron oxides nanoparticles, Hydroxyl radicals, electro-Fenton, Azo-dye

Iron oxide nanoparticles as heterogeneous electro-Fenton catalysts for the removal of AR18 azo-dye

Nouha Ben Hafaiedh, Florence Fourcade, Nizar Bellakhal, Abdeltif Amrane

Introduction:

Advanced oxidation processes (AOPs) are widely documented, owing to their efficiency for the removal of recalcitrant and bio-refractory organic pollutants. AOPs are based on the in situ generation of mainly free hydroxyl radicals [1][START_REF] Jiang | Heterogeneous electro-Fenton oxidation of azo dye methyl orange catalyzed by magnetic Fe3O4 nanoparticles[END_REF][START_REF] Abou Dalle | Efficiency of DMSO as hydroxyl radical probe in an Electrochemical Advanced Oxidation Process -Reactive oxygen species monitoring and impact of the current density[END_REF]. This class of processes includes electro-Fenton, a well-used process thanks to its high performance and relevance for an environmental purpose. Recently, more interest has been given to heterogeneous electro-Fenton [START_REF] Poza-Nogueiras | Current advances and trends in electro-Fenton process using heterogeneous catalysts-A review[END_REF] using zero-valent iron [START_REF] Stieber | Treatment of Pharmaceuticals and Diagnostic Agents Using Zero-Valent Iron -Kinetic Studies and Assessment of Transformation Products Assay[END_REF][START_REF] Xu | A heterogeneous Fenton-like system with nanoparticulate zerovalent iron for removal of 4-chloro-3-methyl phenol[END_REF], iron based clays [START_REF] Papic | Advanced Oxidation Processes in Azo Dye Wastewater Treatment[END_REF][START_REF] Navalon | Heterogeneous Fenton catalysts based on clays, silicas and zeolites[END_REF], iron containing materials [START_REF] Deng | FeVO4 as a highly active heterogeneous Fentonlike catalyst towards the degradation of Orange II[END_REF][START_REF] Luo | Efficient Removal of Organic Pollutants with Magnetic Nanoscaled BiFeO3 as a Reusable Heterogeneous Fenton-Like Catalyst[END_REF] and iron oxides minerals [START_REF] Lin | Quantitative characterization of hydroxyl radical generation in a goethite-catalyzed Fenton-like reaction[END_REF][START_REF] Nidheesh | Magnetite as a heterogeneous electro Fenton catalyst for the removal of Rhodamine B from aqueous solution[END_REF][START_REF] Araujo | Heterogeneous Fenton process using the mineral hematite for the discolouration of a reactive dye solution[END_REF][START_REF] Fang | Superoxide mediated production of hydroxyl radicals by magnetite nanoparticles: Demonstration in the degradation of 2chlorobiphenyl[END_REF]. Great effort have been undertaken to develop active heterogeneous catalysts, such as the use of iron based solid particles [START_REF] Ouiriemmi | Heterogeneous electro-Fenton using natural pyrite as solid catalyst for oxidative degradation of vanillic acid[END_REF][START_REF] Expósito | Mineral Iron Oxides as Iron Source in Electro-Fenton and Photoelectro-Fenton Mineralization Processes[END_REF][START_REF] Nidheesh | Heterogeneous Fenton catalysts for the abatement of organic pollutants from aqueous solution: a review[END_REF][START_REF] Andreozzi | Oxidation of 3,4-dihydroxybenzoic acid by means of hydrogen peroxide in aqueous goethite slurry[END_REF] or hosting iron compounds on different supports [START_REF] Hammouda | Effective heterogeneous electro-Fenton process for the degradation of a malodorous compound, indole, using iron loaded alginate beads as a areusable catalyst[END_REF][START_REF] Poza-Nogueiras | Heterogeneous electro-Fenton as plausible technology for the degradation of imidazolinium-based ionic liquids[END_REF][START_REF] Nidheesh | Heterogeneous Fenton catalysts for the abatement of organic pollutants from aqueous solution: a review[END_REF][START_REF] Rezgui | Electro-Fenton catalyzed with magnetic chitosan beads for the removal of Chlordimeform insecticide[END_REF].

Heterogeneous catalysts can be reused, avoiding catalysts waste and making the process economically feasible. The extended range of pH, from pH 3 to pH 7, is attractive as well. Heterogeneous electro-Fenton is therefore considered as a natural evolution of the homogeneous one [START_REF] Dhakshinamoorthy | Metal Nanoparticles as Heterogeneous Fenton Catalysts[END_REF][START_REF] Rusevova | Nano-sized magnetic iron oxides as catalysts for heterogeneous Fenton-like reactions -Influence of Fe(II)/Fe(III) ratio on catalytic performance[END_REF][START_REF] Kwan | Rates of Hydroxyl Radical Generation and Organic Compound Oxidation in Mineral-Catalyzed Fenton-like Systems[END_REF]. Due to their specific structure, magnetic properties and their abundance, iron oxides such as magnetite (Fe3O4), hematite (Fe2O3) and goethite (α-FeOOH) are the most commonly used [START_REF] Nidheesh | Heterogeneous Electro-Fenton Process: Principles and Applications[END_REF][START_REF] Teja | Synthesis, properties, and applications of magnetic iron oxide nanoparticles[END_REF][START_REF] Garrido-Ramírez | Clays and oxide minerals as catalysts and nanocatalysts in Fenton-like reactions -A review[END_REF].

In the heterogeneous electro-Fenton process, hydroxyl radicals are generated either in solution with dissolved Fe (II) and Fe (III) ions from the catalyst or on its surface [START_REF] Nidheesh | Heterogeneous Fenton catalysts for the abatement of organic pollutants from aqueous solution: a review[END_REF][START_REF] Xu | Fenton-like degradation of 2,4-dichlorophenol using Fe3O4 magnetic nanoparticles[END_REF]. In the latest case, hydrogen peroxide is produced at the cathode then transported by convection to the catalyst surface. Take goethite as an example of heterogeneous Fenton catalyst, two mechanisms can occur on its surface: radical mechanism [START_REF] Shu-Sung | Catalytic Decomposition of Hydrogen Peroxide on Iron Oxide Kinetics, Mechanism, and Implications[END_REF] and non-radical mechanism [START_REF] Roberto | Oxidation of 3,4-dihydroxybenzoic acid by means of hydrogen peroxide in aqueous goethite slurry[END_REF]. In the case of a surface radical mechanism, the reaction starts by the formation of a precursor surface complex (H2O2)s on the surface of the catalyst. (H2O2)s leads then to an electronically excited state ligands through a reversible electron transfer. The unstable formed ligands generate Fe (II) and HO2 • . Fe (II) can then react with either hydrogen peroxide or oxygen to produce • OH and HO2 • respectively. The generated HO2 • will decompose and give place to O2 •-. However, the non-radical mechanism is based on the superficial sites of goethite, which are effective for the sorption of the target substrate and H2O2, reacting on the catalyst surface [START_REF] Xue | Fenton-like oxidation of Rhodamine B in the presence of two types of iron (II, III) oxide[END_REF].

Heterogeneous catalysts based on nanoparticles is a promising alternative [START_REF] Shan | Applications of Nanomaterials in Environmental Science and Engineering: Review[END_REF].

It can have properties that are different from those of the bulk forms of the same material. Nanoparticles present improved catalytic activity [START_REF] Perez | Iron oxide nanoparticles Hidden talent[END_REF], in comparison with their micro-size counterparts, nano-size particles have few or no mass transfer limitations [START_REF] Rusevova | Nano-sized magnetic iron oxides as catalysts for heterogeneous Fenton-like reactions -Influence of Fe(II)/Fe(III) ratio on catalytic performance[END_REF], high surface area [START_REF] Shi | Tuning Catalytic Activity between Homogeneous and Heterogeneous Catalysis: Improved Activity and Selectivity of Free Nano-Fe2O3 in Selective Oxidations[END_REF] and are very reactive thanks to their active sites located on the surface which make them easily accessible [START_REF] Garrido-Ramírez | Clays and oxide minerals as catalysts and nanocatalysts in Fenton-like reactions -A review[END_REF]. A number of studies have shown application of metal nanoparticles as Fenton and electro-Fenton catalysts [START_REF] Dhakshinamoorthy | Metal Nanoparticles as Heterogeneous Fenton Catalysts[END_REF][START_REF] Tang | Magnetic nanoparticles: Essential factors for sustainable environmental applications[END_REF]. Magnetite nanoparticles catalysts were successfully used to degrade methyl orange azo-dye from aqueous solution in the electro-Fenton process [START_REF] Jiang | Heterogeneous electro-Fenton oxidation of azo dye methyl orange catalyzed by magnetic Fe3O4 nanoparticles[END_REF]. In another study, the catalytic behaviour of iron (III) oxide-based nanoparticles was investigated for the treatment of contaminated water. Ethylen glycol and phenol were efficiently destroyed by the Fenton-like reaction in the presence of hydrogen peroxide without ultraviolet (UV) light or any radiation source [START_REF] Grigory | Iron(3) oxide-based nanoparticles as catalysts in advanced organic aqueous oxidation[END_REF]. Moreover, other studies focused on the supported metal nanoparticles, as the degradation of phenol, Rhodamine B and Methyl Blue, which where efficiently degraded using supported Pd and Fe3O4 nanoparticles. Sulfamethazine antibiotics was efficiently degraded as well, using synthesized Fe3O4-Mn3O4 nanocomposite [START_REF] Zhong | Degradation of sulfamethazine antibiotics using Fe3O4-Mn3O4 nanocomposite as a Fenton-like catalyst[END_REF].

In this study, hematite (HNPs) and magnetite (MNPs) nanoparticles were used to oxidize AR18. As reported in literature by Teja et al. [START_REF] Teja | Synthesis, properties, and applications of magnetic iron oxide nanoparticles[END_REF], Magnetite has the strongest magnetism of any transition metal oxide, Fe (III) ions are distributed randomly between octahedral and tetrahedral sites, and Fe (II) ions are distributed in octahedral sites allowing the Fe species to be reversibly oxidized and reduced while keeping the same structure [START_REF] Rusevova | Nano-sized magnetic iron oxides as catalysts for heterogeneous Fenton-like reactions -Influence of Fe(II)/Fe(III) ratio on catalytic performance[END_REF]. The oxygen ions are in cubic close-packed arrangement. However, in hematite, oxygen are in hexagonal close-packed arrangement with Fe (III) ions occupying octahedral sites. This latest is the oldest known of the iron oxides. HNPs and MNPs have shown high catalytic activity for the oxidation of contaminants [START_REF] Araujo | Heterogeneous Fenton process using the mineral hematite for the discolouration of a reactive dye solution[END_REF][START_REF] Fang | Superoxide mediated production of hydroxyl radicals by magnetite nanoparticles: Demonstration in the degradation of 2chlorobiphenyl[END_REF][START_REF] Jiang | Heterogeneous electro-Fenton oxidation of azo dye methyl orange catalyzed by magnetic Fe3O4 nanoparticles[END_REF][START_REF] Luo | An integrated catalyst of Pd supported on magnetic Fe3O4 nanoparticles: Simultaneous production of H2O2 and Fe2D for efficient electro-Fenton degradation of organic contaminants[END_REF][START_REF] Zhong | Degradation of C.I. Acid Orange 7 by heterogeneous Fenton oxidation in combination with ultrasonic irradiation[END_REF]. AR18 dye was chosen as a target compound, since it is extensively employed in food industry, despite its side effects on children behaviour [START_REF] Thiam | Electrochemical reactivity of Ponceau 4R (food additive E124) in different electrolytes and batch cells[END_REF]. Treating AR18 azo dye is reported in literature by electrochemical methods [START_REF] Thiam | Electrochemical reactivity of Ponceau 4R (food additive E124) in different electrolytes and batch cells[END_REF][START_REF] Thiam | Routes for the electrochemical degradation of the artificial food azo-colour Ponceau 4R by advanced oxidation processes[END_REF][START_REF] Malakootian | Efficiency of electro-Fenton process in removing Acid Red 18 dye from aqueous solutions[END_REF]. For Thiam et al. [START_REF] Thiam | Electrochemical reactivity of Ponceau 4R (food additive E124) in different electrolytes and batch cells[END_REF] the photo electro-Fenton (PEF) process in the presence of Fe 2+ catalyst with low or high oxidation power anodes is the most convenient to ensure quick and total removal of AR18 and its by-products after 360 min. Thiam et al. experimented as well, the mineralization of AR18, they achieved 50% TOC removal at 150 mA.cm -2 after 60 min of electrolysis using PEF with BDD anode and 3 cm 2 air-diffusion cathode. The solution was irradiated with 6W lamp of ƛmax =360 nm [START_REF] Thiam | Routes for the electrochemical degradation of the artificial food azo-colour Ponceau 4R by advanced oxidation processes[END_REF]. According to previous studies, AR18 discoloration and mineralization were mainly due to the generation of • OH radicals [START_REF] Thiam | Routes for the electrochemical degradation of the artificial food azo-colour Ponceau 4R by advanced oxidation processes[END_REF][START_REF] Rahmani | Degradation of azo dye C.I. Acid Red 18 using an eco-friendly and continuous electrochemical process[END_REF].

In this work, AR18 mineralization by heterogeneous electro-Fenton process involving hematite and magnetite as nanocatalysts was investigated. The catalysts mass concentrations were examined. Hydrogen peroxide, dissolved iron and hydroxyl radical concentrations were monitored during the mineralization of AR18 using magnetite nanoparticles as catalyst at 50 and 100 mA. The contribution of • OH radicals on mineralization and discoloration was discussed as well.

Materials and methods

Chemicals and materials

AR18 (C20H11N2Na3O10S3, 80%) was obtained as powder from a Tunisian food factory and was used without further purification. Magnetite (Fe3O4, 97%), hematite (Fe2O3, 98%) nano-powders and sodium sulfate (Na2SO4, 99%) were used as catalyst and supporting electrolyte respectively and were purchased from Sigma Aldrich. DMSO (C2H6OS, 99,7%) and sodium methanesulfonate (CH3NaO3S,99%) were purchased form Sigma Aldrich as well. Thiosulfate (Na2S2O3, 98,5%) and analytical grade of sulfuric acid were used as a titrant for hydrogen peroxide quantification and pH adjustment respectively, both were purchased from Acros Organics. 1,10 phenantroline, used for the colorimetric determination of Fe ions was purchased from Alfa Aesar. All solutions were prepared with ultrapure water and all the other chemicals used for analysis were purchased from Acros and Sigma Aldrich.

Electrochemical apparatus and procedure

An electrochemical batch mono-compartment cell with 0.25 L of solution was used to perform all experiments at ambient temperature (20°C). The cell was equipped with, first a cylindrical (Pt) electrode (31.2 cm 2 ) as an anode located in the center of the electrochemical reactor to have a good potential distribution. The second electrode was a tridimensional carbon felt piece (Carbone Lorraine RVG 4000 Mersen, Paris La Defense, France) as a cathode (63mm x50mm x12 mm corresponding to a geometrical volume of 37.8 cm 3 ). AR18 initial concentration was 40 mg L -1 ; all experiments were carried out in duplicate.

The solution was continuously mixed by a magnetic stirrer. The oxygen was provided by bubbling compressed air into the solution (0.5 L.min -1 ) for 10 min, before and all along the electrolysis. The electric field was supplied by an ammeter power supply (Microsinic system, Microlab MX 20V-2A, villette d Anthon, France).

The ionic strength was maintained constant by the addition of 50 mM Na2SO4.

Analytical methods

Total organic carbon (TOC) measurement

The total organic carbon removal of AR18 solution was measured using TOC-VcpH/CPG total organic analyzer Schimadzu. The amount of CO2 formed, through the catalytic combustion and conversion of organic carbon compounds, was quantified using a nondispersive Infra-Red detector (NDIR).

Hydrogen peroxide quantification

The concentration of hydrogen peroxide was determined using iodometric method. H2O2 oxidizes iodide ions to iodine in acidic conditions and in presence of molybdate catalyst, the iodine formed is titrated with thiosulfate solution incorporating the starch indicator [START_REF] Abou Dalle | Efficiency of DMSO as hydroxyl radical probe in an Electrochemical Advanced Oxidation Process -Reactive oxygen species monitoring and impact of the current density[END_REF]. [START_REF] Cadwell | Colorimetric determination of Iron water with Ophenanthroline[END_REF] The concentration of dissolved iron ions (Fe(III)+Fe(II)) was measured by colorimetric determination with 1,10 phenantroline as complexic agent [START_REF] Expósito | Mineral Iron Oxides as Iron Source in Electro-Fenton and Photoelectro-Fenton Mineralization Processes[END_REF]. Its absorbance was measured at 510 nm by a Shimadzu UV-1280 spectrophometer.

Dissolved iron concentration

Hydroxyl radical quantification

The electrochemical cell was the same as described above. It was filled with 50 mM sodium sulfate solution at pH 3. DMSO (0.25 M) and magnetite (40 mg.L -1 ) were added to the solution without AR18. Compressed air was bubbled 10 min prior to electrodes polarization in order to saturate the solution with dissolved oxygen.

The expected hydroxyl radicals were quantified during 180 min of electrolysis at 50 and 100 mA, respectively. Thanks to its high reactivity toward • OH radicals, DMSO is used as a trapping agent to quantify them. In fact, it is oxidized in the medium leading to methanesulfinic acid. This latest will react with two hydroxyl radicals to form methanesulfonate, which can be quantified. Consequently, its quantification leads indirectly to determine the concentration of • OH radicals. Methanesulfonate quantification was performed by ion chromatography (DIONEX DX120, ThemoScientific, Sunnyvale, USA) supplied with a conductivity detector. Mobile phase and stationary phase were KOH and an ion exchange column AS19 (4 x 250 mm), respectively. A gradient elution mode was chosen to run the analysis, 10 mM of KOH during the first 10 min; then increased linearly up to 45 mM after 25 min and this concentration was maintained from 25 to 35 min. The flow rate was set at 1 ml.min -1 [START_REF] Abou Dalle | Efficiency of DMSO as hydroxyl radical probe in an Electrochemical Advanced Oxidation Process -Reactive oxygen species monitoring and impact of the current density[END_REF].

Results and discussion

Effect of catalysts mass concentrations on AR18 mineralization

The crucial role of catalysts in the generation of hydroxyl radicals in electro-Fenton process has been reported by many authors [START_REF] Sun | p-Nitrophenol degradation by a heterogeneous Fenton-like reaction on nano-magnetite: Process optimization, kinetics, and degradation pathways[END_REF][START_REF] Jiang | Heterogeneous electro-Fenton oxidation of azo dye methyl orange catalyzed by magnetic Fe3O4 nanoparticles[END_REF][START_REF] Nidheesh | Magnetite as a heterogeneous electro Fenton catalyst for the removal of Rhodamine B from aqueous solution[END_REF][START_REF] Bouzayani | Removal of polyvinylamine sulfonate anthrapyridone dye by application of heterogeneous electro-Fenton process[END_REF]. Since both homogeneous Fenton reaction and heterogeneous one can occur either in the solution or/and at the catalyst surface, an improvement of the mineralization yield would be expected with an increase of heterogeneous catalyst. Two different commercial nanocatalysts (magnetite and hematite) were evaluated in this study for the mineralization of AR18.

Table 1 shows AR18 mineralization yield achieved after three hours of treatment according to the HNPs mass concentration (40 mg.L -1 or 80 mg.L -1 ). The increase of the HNPs mass concentration amplified only slightly the mineralization yield, from 72.4 ± 0.4 to 75.8 ± 0.4 % at 50 mA and from 81.5 ± 0.2 to 83 ± 1% at 100 mA. In this range of mass concentration, the influence of the hematite catalyst can be considered as negligible. Similar observation was made in the study of Araujo et al. when they studied the oxidation of Drimarene Red X-6BN by heterogeneous Fenton process using hematite as iron nanocatalyst. The increase of mass concentration of hematite from 1 to 5 g.L -1 slightly improved the reactive dye degradation yield. But for 10 g.L -1 of hematite, the dye removal significantly increased [START_REF] Araujo | Heterogeneous Fenton process using the mineral hematite for the discolouration of a reactive dye solution[END_REF]. These results may indicate that in the case of the present study, the range of mass concentration was too low to observe a significant impact. 1] from 40 to 80 mg.L -1 decreased its TOC removal from 81 ± 2 to 55 ±4 % at 50 mA and from 83 ± 2 to 79% ± 2 at 100 mA. Similar results were observed by Nidheesh et al. [START_REF] Nidheesh | Magnetite as a heterogeneous electro Fenton catalyst for the removal of Rhodamine B from aqueous solution[END_REF], and they concluded that the increase in magnetite concentration from 10 to 15 mg.L -1 led to scavenging reactions of excess iron species. Such as the reaction of Fe (III) with H2O2 (reaction 1) to produce HOO • having weaker oxidation capability than • OH radicals. The competition for the consumption of • OH radicals by Fe (II) and H2O2 leads to inefficient consumption of • OH as shown in (reactions 2, 3 and 4). ≡ Fe (III) + H2O2  ≡Fe (III) .H2O2  ≡Fe (II) + HOO• + H + (1)

Contrarily to hematite, an increase of magnetite mass concentration [Table

Fe (II) + •OH  Fe (III) + HO- (2)
•OH + H2O2  HO2• + H2O

• OH  H2O2 (3) 2
At 40 mg.L -1 , Fe (II) -bearing iron mineral, magnetite, is a more effective catalyst than hematite at 50mA for AR18 mineralization and are in accordance with the study of Expósito et al. [START_REF] Expósito | Mineral Iron Oxides as Iron Source in Electro-Fenton and Photoelectro-Fenton Mineralization Processes[END_REF]. They tested hematite and magnetite as electro-Fenton heterogeneous catalyst for aniline removal. Based on their results, homogeneous Fenton reaction was mainly responsible for the oxidation of aniline and the lowest mineralization yield was obtained for hematite because of the low iron ions leaching from the catalyst.

Influence of the applied current intensity

Current intensity is an important parameter considering its direct implication in the process operating cost, the regeneration of ferrous catalyst at the cathode (reaction 1)

and the generation of H2O2 (reaction 5) [START_REF] Da | Functional group influences on the reactive azo dye decolorization performance by electrochemical oxidation and electro-Fenton technologies[END_REF]. An increase in both Fe (II) and H2O2 as a result of an increase of the current intensity leads to a higher production of • OH radicals, inducing a higher mineralization of the dye.

O2+2H + +2e- H2O2 (5)
With HNPs catalyst [table 1], the mineralization yield increased when the current intensity varied from 50 mA to 100 mA; from 72.4 ± 0.4 to 81.5 ±0.2 % in the presence of 40 mg.L -1 of catalyst and from 75.8 ±0.4 to 83.3 ±0.3% with 80 mg.L -1 catalyst.

On one hand, kinetic rate of H2O2 production can be increased with current intensity (reaction 5) and on the other hand the oxidation of water at the anode can lead to a greater production of O2 (Reaction 6) [START_REF] Nidheesh | Magnetite as a heterogeneous electro Fenton catalyst for the removal of Rhodamine B from aqueous solution[END_REF].

H2O ↔1/2 O2 + 2H + + 2 e - (6)
With MNPs catalyst, mineralization yield at 50 and 100 mA for 40 mg.L -1 recorded a slight increase from 81 ± 2 to 83 ± 2%. Mineralization yield then decreased to 71 ± 2% when current intensity achieved 250 mA. Almost the same trend was observed for 80 mg.L -1 , since a maximum was also observed for 100 mA.

From 50 to 100 mA, the evolution of the mineralization yield was in accordance with the slight increase of the amount of H2O2 generated, from 0.9 ± 0,06 mM to 1.15 ± 0,09 mM after 120 min of electrolysis (data not shown). The decrease of mineralization yield at 250 mA for magnetite can be then explained considering competitive reactions such as the electro reduction of H2O2 (reaction 7), its dismutation in solution (reaction 8), its anodic oxidation (reaction 9) and the hydrogen production (reaction 10) [START_REF] Abou Dalle | Efficiency of DMSO as hydroxyl radical probe in an Electrochemical Advanced Oxidation Process -Reactive oxygen species monitoring and impact of the current density[END_REF].

H2O2+2H + +2e-2H2O (7) 2H2O2  O2 +2H2O (8)
H2O2  O2 + 2e -+ 2H + (9)

2H + + 2e - H2 (10)
The iron dissolution during electrolysis with MNPs was studied and the evolution of soluble Fe ions (ferric + ferrous ions) is represented in figure 1 for two current intensities (50 and 100 mA). For the first 30 min of electrolysis a high Fe ions dissolution was observed for both current intensities (50 and 100 mA); then the concentration of dissolved iron species increased with the reaction time until remaining constant after 120 min. The concentration of iron in solution was higher for 100 mA than for 50 mA. The influence of current intensity on the dissolution of ferrous ions and their regeneration was also observed previously [START_REF] Xu | Fenton-like degradation of 2,4-dichlorophenol using Fe3O4 magnetic nanoparticles[END_REF][START_REF] Luo | An integrated catalyst of Pd supported on magnetic Fe3O4 nanoparticles: Simultaneous production of H2O2 and Fe2D for efficient electro-Fenton degradation of organic contaminants[END_REF]. Nideesh et al. [START_REF] Nidheesh | Heterogeneous Fenton catalysts for the abatement of organic pollutants from aqueous solution: a review[END_REF] also found that the increase of electrode potential favor the leaching of metals from magnetite, affecting consequently the pollutant degradation mechanism from surface reaction to Fenton reaction in solution.

Based on these findings the slight increase in TOC removal from 50 mA to 100 mA can be attributed to the enhancement of H2O2 and dissolved iron species production and a better Fe (II) generation leading to the production of higher amount of • OH radicals.

According to Nideesh et al. [START_REF] Nidheesh | Heterogeneous Electro-Fenton Process: Principles and Applications[END_REF], a high catalysts leaching induces the generation of

• OH radicals in the bulk solution. In contrast, when insignificant iron leaching is observed, • OH radicals are generated over the catalyst surface. In the current study, high amount of dissolved iron from magnetite 1.39 ± 0.05 mM at 100 mA and 1.20 ± 0.02 mM at 50 mA in the bulk solution was found (Figure 1). If we consider 2.07 mM as the initial theoretical concentration of iron from the catalyst (40 mg.L -1 of Fe3O4 in 250 mL), 67% at 100 mA and 58% at 50 mA of total iron were leached in solution after 180 min indicating that homogeneous Fenton reaction plays a major rule in the mechanism of • OH radicals generation, which is in agreement with the related literature [START_REF] Luo | An integrated catalyst of Pd supported on magnetic Fe3O4 nanoparticles: Simultaneous production of H2O2 and Fe2D for efficient electro-Fenton degradation of organic contaminants[END_REF][START_REF] Matta | Fenton-like oxidation of 2,4,6-trinitroluene using different iron minerals[END_REF]. Exposito et al. [START_REF] Expósito | Mineral Iron Oxides as Iron Source in Electro-Fenton and Photoelectro-Fenton Mineralization Processes[END_REF] measured the concentration of total Fe dissolved in the solution; it was 21.2 mg.L -1 , after 24h of electro-Fenton treatment using 1g/L Fe3O4 catalyst. They suggested that magnetite behaves as iron ions in the solution; accordingly the homogeneous catalytic reaction is dominant and the heterogeneous catalytic reaction can be considered as negligible in the mineralization of organic compounds. Xu et al.

[28] investigated the Fenton-like degradation of 2,4-dichlorophenol using Fe3O4 magnetic nanoparticles. The concentration of total dissolved iron increased as reaction time increased, which can be attributed to the continuous leaching of iron from 1g/L MNPs, achieving 9.8 mg.L -1 of the iron dissolved into the solution after 180 min. They stipulated that the degradation occurs in two stages, an induction and a degradation stage. Induction period is considered as an activation stage involving the dissolution of iron and the second stage is attributed mainly to the bulk homogeneous Fenton reaction [START_REF] Xu | Fenton-like degradation of 2,4-dichlorophenol using Fe3O4 magnetic nanoparticles[END_REF].

In this way, the evolution of the • OH radicals concentration was carried out at the two tested current intensities (Figure 2). Results showed a higher hydroxyl radical production rate for 100 mA in comparison to 50 mA up to 60 min of electrolysis (2 10 -4 mM.s -1 and 10 -4 mM.s -1 respectively); these results were in accordance with those obtained for H2O2 generation and iron ion leaching. Moreover, there were in accordance with the AR18 mineralization yield behavior.

Contribution of •OH

It is important to elucidate the contribution of hydroxyl radicals to AR18 discoloration and mineralization in electro-Fenton process with magnetite as iron catalyst. To do so the contribution of hydroxyl radicals was investigated by radical scavenging.

Isopropanol in excess (1 M) was chosen as scavenger due to its high reaction rate constant with • OH radicals (1.9x10 9 ) L mol -1 s -1 [START_REF] Buxton | Critical Review of Rate Constants for Reactions of Hydrated Electrons, Hydrogen Atoms and Hydroxyl Radicals (•OH/•O-) in Aqueous Solution[END_REF]. As presented in figure 3, only 26% at 50 mA and 30% at 100 mA TOC removal were achieved in the same experimental conditions. However, the discoloration percentage remained unchanged, achieving total discoloration after 15 min of electrolysis at 50 and 100 mA , with excess isopropanol (1 M) with 40 mg.L -1 Fe3O4 at pH 3 in 250 mL Na2SO4 0.05 M (data not shown).

Based on these results, it can be concluded that • OH radicals were responsible for more than 50% of the TOC removal. The AR18 discoloration through cleavage of its chromophore groups [START_REF] Bouzayani | Removal of polyvinylamine sulfonate anthrapyridone dye by application of heterogeneous electro-Fenton process[END_REF] was faster than its mineralization but did not depend on hydroxyl radicals oxidation.

To better understand the degradation mechanism, cyclic voltammetry curves were plotted in AR18 solutions, recorded in oxidation and in reduction at 200 mg.L -1 of AR18 in 0.05 M sodium sulfate solution at pH 3.0 and at 20°C, using vitreous carbon as working electrode (figure 4). In the presence of AR18 an oxidation peak appeared at 0.4V/ECS which led to the conclusion that apart from mediated •OH, AR18 is electroactive and may undergo direct oxidation as well. This can account for the rapid discoloration. This finding is in agreement with Thiam et al.

Conclusion

Heterogeneous electro-Fenton mineralization of Acid Red18 in aqueous solution was studied with hematite and magnetite as nanocatalysts. In the range of hematite amounts tested, its impact on the mineralization yield was not significant. The increase of the mass concentration of magnetite affected mineralization due to scavenging reactions.

However, the highest TOC removal was achieved for magnetite; 83±2% at 100 mA for

  [START_REF] Thiam | Electrochemical reactivity of Ponceau 4R (food additive E124) in different electrolytes and batch cells[END_REF]. Moreover, other reactive oxygen species ROS and adsorption phenomena may contribute to the mineralization of the pollutant. Wang et al.[START_REF] Wang | Sono-assisted preparation of highly-efficient peroxidase-like Fe3O4 magnetic nanoparticles for catalytic removal of organic pollutants with H2O2[END_REF] investigated the nature of ROS generated from the decomposition of H2O2 catalyzed by Fe3O4 MNPs as peroxidase mimetic. They identified the produced ROS with the electron spin resonance (ESR) measurement by the addition of the spin-trapping DMPO, showing that •OH and O2 -• /HO2 • radicals are formed and contribute to the pollutant mineralization.

Figure 1 . 22 Figure 2 . 23 Figure 3 .Figure 4 .

 12222334 Figure 1. Investigation of Fe ion dissolution as a function of the current intensity during 180 min, with 40 mg.L -1 Fe3O4, at pH 3, in 250 mL Na2SO4 0.05M


Ahmad Abdallah

Stéphane Freslon

Xiao Fan

Amandine Rojo

Carole Daiguebonne

Yan Suffren

Kevin Bernot

Guillaume Calvez

Thierry Roisnel

Olivier Guillou

Lanthanide-Based Coordination Polymers With 1,4-Carboxyphenylboronic Ligand: Multiemissive Compounds for Multisensitive Luminescent Thermometric Probes

come

ABSTRACT.

Reactions in water of lanthanide chlorides with the sodium salt of 1,4-carboxyphenylboronic acid (Hcpb) lead to two series of isostructural compounds with respective general chemical formulas [Ln(cpb) 3 (H 2 O) 2 ] ∞ for Ln = La or Ce and [Ln(cpbOH)(H 2 O) 2 •(cpb)] ∞ for Ln = Pr-Lu (except Pm) plus Y. Hetero-lanthanide coordination polymers that are isostructural to the second series have been synthesized and their photo-physical properties have been studied. This study evidences that it is possible to design multi-emissive lanthanide-based coordination polymers that could find their application as multi-gauge luminescent thermometric probes.

INTRODUCTION.

In the last two decades, there was a growing interest for lanthanide-based coordination polymers because of their fascinating crystal structures [START_REF] Alezi | Quest for highly connected metal-organic framework platforms : rara earth polynuclear clusters versatility meets net topology needs[END_REF][START_REF] Guillerm | Discovery and introduction of a (3,18)-connected net as an idel blueprint for the design of metal-organic frameworks[END_REF][START_REF] Le Natur | Extending the lanthanide terephthalate system : isolation of an unprecedented Tb(III)-based coordnation polmer with high potential porosity and luminescence properties[END_REF][START_REF] Luo | 1,2,4,5-benzene-tetra-carboxylic acid : A versatile ligand for high dimensionnal lanthanide-based coordination polymers[END_REF] as well as their interesting porosity, [START_REF] Eddaoudi | Systematic Design of Pore Size and Functionnality in Isoreticular MOFs and their application in Methane Storage[END_REF][START_REF] Reneike | From Condensed Lanthanide Coordination Solids to Microporous Frameworks Having Accessible Metal sites[END_REF][START_REF] Kerbellec | New lanthanide based coordination polymers with high potential porosity[END_REF][START_REF] Devic | MIL-103, A 3-D Lanthanide Based Metal Organic Framework with Large One Dimensionnal Tunnels and a High Surface area[END_REF] magnetic [START_REF] Calvez | Sterically-induced synthesis of 3d-4f one-dimensional compounds: a new route towards 3d-4f Single Chain Magnets[END_REF][START_REF] Bernot | Spin canting in a Dy-based single-chain magnet with dominant next-nearest-neighbor antiferromagnetic interactions[END_REF][START_REF] Jeon | Controlled association of single-molecule magnets (SMMs) into coordination networks: towards a new generation of magnetic materials[END_REF] and optical properties. [START_REF] Cui | Metal-organic frameworks as platforms for functionnal materials[END_REF][START_REF] Li | Multifunctionnal lanthanide coordination polymers[END_REF][START_REF] Bünzli | On the design of highly luminescent lanthanide complexes[END_REF][START_REF] Cui | Photonic functional metal-organic frameworks[END_REF] Because of their unique optical properties lanthanide-based coordination polymers can be suitable for potential applications in various fields such as lighting and display, [START_REF] Bünzli | On the design of highly luminescent lanthanide complexes[END_REF][START_REF] Bünzli | Rising stars in science and technology : Luminescent lanthanide materials[END_REF][START_REF] Li | Luminescence modulation, white light emission and energy transfer in a family of lanthanide Metal-Organic Frameworks based on a planar -conjugated ligand[END_REF] chemical sensing, [START_REF] Dang | Lanthanide metal-organic frameworks showing luminescence in the visible and near infrared regions with potential for acetone sensing[END_REF] fight against counterfeiting [START_REF] Guillou | A long journey in lanthanide chemistry : from fundamental crystallogenesis studies to commercial anti-counterfeiting taggants[END_REF][START_REF] Yang | Linear dependance of photomuminescence in mixed Ln-MOFs for color tunability and barcode application[END_REF][START_REF] Andres | A new counterfeiting feature relying on invisible luminescent full color images printed with lanthanide-based Inks[END_REF] or thermometric probes, [START_REF] Rao | A highly sensitive mixed lanthanide metal organic framework self calibrated luminescent thermometer[END_REF][START_REF] Cui | A Luminescent Mixed-Lanthanide Metal-Organic Framework Thermometer[END_REF][START_REF] Cui | A ratiometric and colorimetric luminescent thermometer over a wide temperature range based on a lanthanide coordination polymer[END_REF][START_REF] Cui | Dual emitting MOF-Dye composite for ratiometric temperature sensing[END_REF][START_REF] Cadiau | Ratiometric nanomether based on an emissive Ln 3+ -organic framework[END_REF][START_REF] Chuasaard | Lanthanide coordination polymers of mixed phthalate/adipate for ratiometric temperature sensing in the upper-intermediate temperature range[END_REF][START_REF] Brites | Lanthanide-based luminescent molecular thermometers[END_REF][START_REF] Rocha | Lanthanide organic framework luminescent thermometers[END_REF][START_REF] Zhou | A bimetallic lanthanide metal-organic material as a self-calibrating color-gradient luminescent sensor[END_REF][START_REF] Ren | A cryogenic luminescent ratiometric thermometer based on lanthanide phosphonate dimer[END_REF][START_REF] Wang | Multifunctionnal chemical sensors and luminescent thermometers based on lanthanide metal-organic framework materials[END_REF][START_REF] An | Synthesis, structure, white light emission and temperature recognition properties of Eu/Tb mixed coordination polymers[END_REF][START_REF] Yang | A family of doped lanthanide metal organic frameworks for wide-range temperature sensing and tunable white light emission[END_REF][START_REF] Zhou | Color tunable emission and low-temperature luminescent sensing of europium and terbium carboxylic acid complexes[END_REF][START_REF] Khudoleeva | Terbium-europium fluorides surface modified with benzoate and terephthalate anions for temperature sensing : Does sensitivity depends on the ligand ?[END_REF][START_REF] Song | Mixed lanthanide coordination polymers for temperature sensing and enhanced Nd III NIR luminescence[END_REF] for examples. Some of these applications require the use of hetero-lanthanide coordination polymers whose first example has been reported in 1994 by Zhou et al. [START_REF] Zhou | Synthesis, characterization, crystal structure and luminescent property studies on a novel heteronuclear lanthanide complex {H[EuLa 2 (DPA) 5 .8H 2 O].8H 2 O} n (H 2 DPA=pyridine-2,6-dicarboxylic acid)[END_REF] Our group is involved in that field for more than a decade and the search of new ligands that lead to new hetero-lanthanide coordination polymers with original luminescence properties is a continuous concern. [START_REF] Badiane | High britness and easy color modulation in lanthanide-based coordination polymers with 5-methoxyisophthalate as ligand: Toward emission colors additive strategy[END_REF][START_REF] Freslon | Brightness and color tuning in a series of lanthanide-based coordination polymers with benzene 1,2,4,5-tetracarboxylic acid as ligand[END_REF][START_REF] Freslon | Influence of photo-induced electron transfer on lanthanide-based coordination polymers luminescence : A comparison between two pseudo-isoreticular molecular networks[END_REF][START_REF] Fan | Heteronuclear lanthanide-based coordination polymers exhibiting tunable multiple emission spectra[END_REF][START_REF] Haquin | Color and Brightness tuning in heteronuclear lanthanide teraphthalate coordination polymers[END_REF][START_REF] Badiane | Lanthanide based coordination polymers with a 4,5-dichlorophthalate ligand exhibiting highly tunable luminescence : Toward luminescent bar codes[END_REF] This article is devoted to the study of hetero-lanthanide based coordination polymers with 4-carboxyphenylboronic acid (Hcpb) as ligand (Scheme 1). This ligand has been chosen because of its rode-like topology, its low toxicity [START_REF] Hall | Boronic acids[END_REF] and its ability to behave as both a Lewis and a Bronstëd acids. Moreover, it can act as a structuring ligand via -stacking and hydrogen bonds. At last, examples of coordination compounds based on boronate ligands are rather scarce [START_REF] Sene | Coordination networks based on boronate and benzoxaborolate ligands[END_REF][START_REF] Lekshmi | First study of metal hybrids of boronic acis : Second sphere coordination networks in the structures of 4-carboxyphenylboronic acid with some transition metal ions[END_REF] and, to the best of our knowledge, there is to date only two examples of lanthanide-based coordination polymers with such ligands. [START_REF] Fan | A family of lanthanide based coordination polymers with boronic acid as ligand[END_REF][START_REF] Yang | Boric acid functional lanthanide metal organic frameworks for selective ratiometric fluorescence detaction of fluoride ions[END_REF] Scheme 1. Schematic representation of the 1,4-carboxyphenylboronic acid hereafter symbolized by Hcpb EXPERIMENTAL SECTION.

Synthesis and characterization of the starting salts.

1,4-carboxyphenylboronic acid (Hcpb) (>90%) was purchased from Sigma Aldrich and used without any further purification. By recrystallization in water, two different polymorphous phases were isolated depending on the recrystallization process. One out of the two crystal structures was still unknown. It has chemical formula Hcpb•0.25H 2 O. Its crystal and final structure refinement data as well as projection views of the asymmetric unit and of the crystal packing are reported in Table S1 and Figures S1 andS2 respectively. Crystal structure of Hcpb has been reported previously (CCDC-247776). [START_REF] Lekshmi | Solid state structure of 4-carboxyphenylboronic acid and its hydrates[END_REF] This very rich polymorphic system (four different crystal structures reported to date) confirms that this ligand is able to provide various structuring intermolecular interactions (Table 1). Powder diffraction diagram and thermal analysis of the commercial microcrystalline powder revealed that it is isostructural to Hcpb (Figures S3 andS4). Sodium salt of 1,4-carboxyphenylboronic acid was prepared by addition of one equivalent of sodium hydroxide to a suspension of the acid in water. The pH was then adjusted to 9 by another addition of sodium hydroxide to the mixture. The obtained clear solution was then evaporated to dryness and the resulting solid washed with ethanol.

Precipitation occurred after ethoxyethane addition. The precipitate was then filtered and dried in air. The yield was about 90%. Thermal analyses show that the salt is Nacpb•1.5H 2 O (Figure S5). Some single crystals suitable for single crystal X-ray diffraction analysis were obtained by recrystallization in water. In this crystal structure the sodium salt is twice hydrated (Nacpb•2H 2 O). Crystal and final structure refinement data as well as a projection view of the asymmetric unit are reported in Table S2 and Figure S6.

Lanthanide oxides (4N) were purchased from AMPERE Company and used without further purification. Lanthanide chlorides were prepared according to established procedures. [START_REF] Desreux | Lanthanide Probes in Life, Chemical and Earth Sciences[END_REF] Synthesis of the lanthanide-based coordination polymers as microcrystalline powders.

Homo

[Ln(cpbOH)(H 2 O) 2 •(cpb)] ∞ that is hereafter abbreviated as [Ln(cpbOH)] ∞ .
Crystal structure of compounds that constitute the former family is described hereafter. Crystal structure of compounds of the latter family have previously been described. [START_REF] Fan | A family of lanthanide based coordination polymers with boronic acid as ligand[END_REF] Hetero-lanthanide based coordination polymers were synthesized according to the same procedure simply replacing the lanthanide chloride solution by a mixture of lanthanide chlorides solution. All hetero-lanthanide compounds have been assumed to be isostructural to [Tb(cpbOH)] ∞ [START_REF] Fan | A family of lanthanide based coordination polymers with boronic acid as ligand[END_REF] on the basis of their powder X-ray diffraction diagrams (Figures S8 to S14).

For all of them, relative contents of the different lanthanide ions have been estimated by EDS measurements (Table S3). On the basis of previous 89 Y solid state NMR spectroscopy studies realized on similar compounds, [42-43, 48, 52] it has been assumed that lanthanide ions are randomly distributed over all the metallic sites of the crystal structure.

Crystal growth of the single crystals of [La(cpb) 3 ] ∞ .

Tetramethylorthosilicate (TMOS) was purchased from Acros Organics and jellified according to established procedures. [START_REF] Henisch | Crystals in Gels and Liesegang Rings[END_REF][START_REF] Henisch | Crystal Growth in Gels[END_REF][START_REF] Daiguebonne | Lanthanide-based molecular materials : gel medium induced polymorphism[END_REF] Aqueous solutions of a lanthanum chloride in one hand and of the sodium salt of 1,4-carboxyphenylboronic acid in the other hand were allowed to slowly diffuse through a TMOS gel (7.5% in weight) in a U-shaped tube. After a few weeks, needle-like single crystal suitable for X-ray diffraction were collected and sealed in capillaries in order to avoid any potential dehydration.

Single crystal X-ray diffraction.

Single crystals were mounted on a Nonius Kappa CCD Bruker diffractometer for [La(cpb) 3 ] ∞ and on a D8 Venture Bruker diffractometer for the other compounds. Crystal data collections were performed with MoK α radiation (λ = 0.70713 Å) at room temperature for [La(cpb) 3 ] ∞ and Nacpb•2H 2 O, and at 150 K for the other compound. Crystal structures were solved by direct methods using the SIR97 program [START_REF] Altomare | EXPO: a program for full powder pattern decomposition and crystal structure solution[END_REF] and then refined with full matrix least-squares methods based on F 2 (SHELX97) [START_REF] Sheldrick | SHELXL : High-Resolution Refinement[END_REF] with the aid of WINGX program. [START_REF] Farrugia | WinGX suite for smallmolecule single-crystal crystallography[END_REF] All non-hydrogen atoms were refined anisotropically using the SHELXL program. Hydrogen atoms bound to the organic ligand were located at ideal positions except those of the -B(OH) 3

groups in [La(cpb) 3 ] ∞ crystal structure. Hydrogen atoms of water molecules were not localized. Absorption correction were performed using WinGX program facilities. [START_REF] Farrugia | WinGX suite for smallmolecule single-crystal crystallography[END_REF][START_REF] Sluis | BYPASS: an Effective Method for the Refinement of Crystal Structures Containing Disordered Solvent Regions[END_REF] Full details of the X-ray structure determination of the crystal structures of Hcpb•0.25H Powder X-ray diffraction.

Experimental diagrams have been collected with a Panalytical X'pert Pro diffractometer equipped with an X'Celerator detector(45 kV, 40 mA for CuK  ( = 1.542Å) in / mode). Calculated diagrams were produced using the Powdercell and WinPLOTR software programs. [START_REF] Kraus | POWDER CELL -A program for the representation and manipulation of crystal structures and calculation of the resulting X-ray powder patterns[END_REF][START_REF] Roisnel | A Window Tool for Powder Diffraction Patterns Analysis[END_REF][START_REF] Roisnel | WinPLOTR : a windows tool for powder diffraction pattern analysis[END_REF] Optical measurements.

Luminescence spectra (emission and excitation) have been realized on a Horiba Jobin-Yvon Fluorolog III fluorescence spectrometer. This device has been equipped with a Xe lamp 450 W, an UV-Vis photomultiplier (PMT Hamamatsu R928, sensitivity range = 190-860 nm) and an infrared-photodiode cooled by liquid nitrogen (InGaAs, sensitivity range = 800-1600 nm). Classical emission and excitation have been measured on the solid state at room temperature. Quantum yields were measured using a integrating sphere from Jobin-Yvon company thanks to the following formula : E c -E a )/(L a -L c ) (E c and L c are the integrated emission spectrum and the absorption at the excitation wavelength of the sample, while E a and L a are the integrated "blank" emission spectrum and "blank" absorption, respectively). Quantum yield recordings and emission/excitation spectra were performed on powder samples introduced in cylindrical quartz cells of 2.4 cm height and 0.7 cm diameter, which were placed inside the integrating sphere. For the IR emissions, powder samples were pasted on copper plates with silver glue or introduced directly in quartz capillary tubes. The Gd-based phospho-luminescence has been realized at 77 K, the powder was placed in a quartz capillary tube, which was introduced inside a small Dewar filled by liquid nitrogen. Emissions and excitations at variable temperature were performed with an optical cryostat coupled with an external liquid nitrogen bath, able to reach temperature of 77 K under nitrogen gas media.

Luminescence decays were measured at room-temperature using a Xenon flash lamp (phosphorescence mode) from the Fluorolog III spectrometer. Quantum yields and luminescence decays are averages of two or three independent determinations.

Comparative solid state luminescent spectra have been measured on powders samples shaped into pellets using the Fluorolog III fluorescence spectrometer between 450 and 725 nm under identical operating conditions. The Xenon lamp was maintained switch on during all the measurements to ensure a valid comparison between the emission spectra.

For all the measurements recorded, the residual excitation laser light, the Rayleigh scattered light and associated harmonics from spectra (emission, excitation, decay, quantum yield) were removed with appropriate filters. All spectra were corrected for the instrumental response function.

Luminescence intensities (in Cd.m -2 ) of the powders have been measured using a

Gigahertz-Optik X1-1 optometer (integration time = 200 ms) on 1.5 cm 2 pellets under UV irradiation ( exc = 312 nm). The UV flux (in mW.cm -2 ) at sample location has been measured

using a VilberLourmat VLX-3W radiometer. [Tb 2 (bdc) 3 •4H 2 O]  compound where bdc 2-
stands for terephthalate was used as a reference. Its luminance value is 107 Cd.m -2 under 312 nm irradiation and a flux of 0.793 mW.cm -2 . [START_REF] Haquin | Color and Brightness tuning in heteronuclear lanthanide teraphthalate coordination polymers[END_REF] Solution and solid state UV-visible absorption spectra have performed using a Perkin Elmer Lambda 650 spectrometer equipped with a 60 mm integrated sphere.

Colorimetric measurements.

The CIE (Commission Internationale de l'Eclairage: 2°, CIE 1931, step 5 nm) (x, y) emission color coordinates [START_REF] Cie | International Commission on Illumination -Technical report[END_REF][START_REF] Wyszecki | Colorimetry[END_REF] were measured using a MSU-003 colorimeter with the PhotonProbe 1.6.0 Software from Majantys. Color measurements were realized under 312 nm

UV light: X = 𝑘 × ∫ 𝐼 𝜆 × 𝑥 𝜆 780𝑛𝑚 380𝑛𝑚 , Y = 𝑘 × ∫ 𝐼 𝜆 × 𝑦 𝜆 780𝑛𝑚 380𝑛𝑚 and Z = 𝑘 × ∫ 𝐼 𝜆 × 𝑧 𝜆 780𝑛𝑚 380𝑛𝑚
with k constant for the measurement system, I  sample spectrum intensity wavelength depending,

Thermal analyzes.

Thermal analyzes were performed with a Perkin-Elmer STA6000 TG/DSC analyzers in the 20-900°C temperature range under N 2 atmosphere in ceramic crucibles.

Electronic microscopy and Energy Dispersive Spectroscopy (EDS).

EDS measurements have been performed with a Hitachi TM-1000 Tabletop

Microscope version 02.11 (Hitachi High-Technologies, Corporation Tokyo Japan) with EDS analysis system (SwiftED-TM, Oxford Instruments Link INCA). Samples were deposited on carbon discs pasted on an aluminium stub located at 7 mm from EDX beam, with an angle of measurement of 22°. Reproducibility of the elemental analyses has been checked by repeating the measurements several times. These experiments support the homogeneity of the samples.

RESULTS AND DISCUSSION.

Reactions in water of lanthanide chlorides and the sodium salt of The crystal structure can be described as the superimposition of one dimensional There is only one independent La 3+ ion in the crystal structure. It is eight-coordinated by six oxygen atoms from six carboxylate functions from different cpb -ligands and by two oxygen atoms from coordination water molecules that generate a bi-augmented trigonal prism (C 2v site symmetry). There are three independent cpb -ligands but all three adopt the same bridging coordination mode (Figure 2): the carboxylate function links two different La 3+ ions in a unidentate manner while the boronic function is free and only involved in the inter-chains hydrogen-bonds network.

From a global point of view, there are two different types of ligands: Type A that links lanthanum ions along the b direction and form two linear chains that spread parallel to the b axis and type B that binds lanthanum ion that belong to different chains (See Figure 2). Coordination polymers that are obtained with one of the rare earth comprised between praseodymium and lutetium (except promethium) or yttrium are all isostructural with [Tb(cpbOH)] ∞ whose crystal structure has been reported previously (CCDC-962513). [START_REF] Fan | A family of lanthanide based coordination polymers with boronic acid as ligand[END_REF] Its crystal structure is two-dimensional and can be described on the basis of wavy planes that spread parallel to the ab plane. In the inter-planes space isolated cpb -ligands insure the electro-neutrality of the crystal packing (See figure 3). As far as luminescent properties are targeted, this second family of compounds is the most interesting one because it contains all the lanthanide ions that can emit in the visible or NIR regions. As a consequence, intermetallic distances between lanthanide ions have to be carefully considered because they influence intermetallic energy transfers efficiency. In this crystal structure, chains of lanthanide ions spread along the a axis. In these chains, the shortest distances between neighboring lanthanide ions are 5.3 Å and 4.3 Å. These chains are bound to each other by cpb -ligands to form wavy molecular planes. The shortest distances between lanthanide ions that belong to neighboring chains are 9.8 Å. Last, the shortest distances between lanthanide ions that belong to different wavy planes are 9.6 Å. For estimating the mean distance between lanthanide ions in the crystal structure, it is possible to use the rough model that has already been used successfully previously. [START_REF] Luo | Synthesis, Crystal Structure and Luminescent Properties of New Lanthanide-Containing Coordination Polymers Involving 4,4'-oxy-bis-benzoate as Ligand[END_REF] In this model, the mean volume occupied by a lanthanide ion is calculated as the cell volume (3588 Å 3 ) divided by the number of lanthanide ions in the unit cell (Z = 8). This mean volume corresponds to a sphere with a 4.75 Å radius which suggests that the mean distance between two lanthanide ions is roughly 9.5 Å which. Therefore, according to this model, a dilution by 10% of the optically active lanthanide ions would reduce significantly inter-metallic energy transfers.

Indeed, it is usually considered that inter-metallic energy transfers become less efficient when there is no acceptor lanthanide ion closer than 10 Å from a given lanthanide ion. [START_REF] Dexter | A theory of sensitized luminescence in solids[END_REF][START_REF] Förster | Comparative effects of radiation[END_REF] This can be achieved by dilution of optically active lanthanide ions by non-acceptor lanthanide ions (such as Gd 3+ , Y 3+ or Lu 3+ for instance). = 400 nm = 25000 cm -1 ) of [Gd(cpbOH)] ∞ (Figure S15). [START_REF] Shi | Tuning the Triplet Energy Levels of Pyrazolone Ligands to Match the 5 D 0 Level of Europium(III)[END_REF][START_REF] Prodi | Luminescent Eu3+, Tb3+ and Gd3+ complexes of a branched triazacyclononane ligand containing three 2,2'bipyridine units[END_REF][START_REF] Bünzli | Basics of lanthanide photophysics[END_REF] According to Reinhoudt's empirical rule, the intersystem crossing process becomes effective when ∆E ( 1 ππ*-3 ππ*) is at least 5000 cm -1 . [71] In this compound, the gap between the singlet and the triplet exited state (5750 cm -1 ) is favorable for an efficient intersystem crossing process.

Solid-state luminescent properties have been recorded in visible or near IR regions for

[Ln(cpbOH)] ∞ with Ln = Nd, Sm, Eu, Tb, Dy and Ho. These measurements show that an antenna effect [START_REF] Weissman | Intramolecular energy transfer -The fluorescence of complexes of europium[END_REF] is observed for all the compounds. Most emitting homo-lanthanide compounds are those which are based on Nd 3+ , Eu 3+ or Tb 3+ (Figure 4). This is in agreement with Latva's empirical rule [START_REF] Latva | Correlation between the lowest triplet state energy level of the ligand and lanthanide luminescence quantum yields[END_REF] that predicts that the energy of the first excited triplet state (25000 cm -1 ) allows good ligand-to-metal energy transfer without significant back transfer for Tb 3+ ( 5 D 4 → 7 F 6-0 transitions) and Eu 3+ ( 5 D 0 → 7 F 0-4 transitions). Despite its low luminescent energy level, an antenna effect is also observed for the Nd 3+ -based compound ( 4 F 3/2 → 4 I 9/2 , 4 I 11/2 , 4 I 13/2 transitions) (Scheme 3). Scheme 3. Simplified Dieke-Jablonsky diagram for emissive lanthanide ions.

Excitation and emission spectra of [Ln(cpbOH)] ∞ with Ln = Sm 3+ , Dy 3+ or Ho 3+ are reported in (Figure S16). Their weak luminescence can be related to their small energy gaps. [START_REF] Eliseeva | Lanthanide luminescence for functionnal materials and biosciences[END_REF] Overall luminescent quantum yields and observed lifetime for both the Eu-and the Tb-based homo-lanthanide compounds have been measured. They are reported in Table 3.

These results complete and confirm previously reported results about Tb-and

Eu-derivatives. [START_REF] Fan | A family of lanthanide based coordination polymers with boronic acid as ligand[END_REF] Because thermometric probe application is targeted, dependence upon temperature of solid state luminescence of the three most luminescent homo-nuclear compounds has been studied in the 77 K -293 K range (Figure 5). In the following, luminescence intensity of a given lanthanide ion will be assumed to be proportional to the integrated intensity of the most intense characteristic emission peak of this lanthanide ion, that is the one centered at 544.5 nm for Tb 3+ ( 5 D 4  7 F 5 ), the one centered at 611.5 nm for Eu 3+ ( 5 D 0  7 F 2 ) and the one centered at 1055 nm for Nd 3+ ( 4 F 3/2 → 4 I 11/2 ). It will be symbolized hereafter by I Ln . Figure 5 shows that luminescence of homo-nuclear Nd 3+ -based compound is only weakly influenced by temperature while the one of the homo-nuclear Eu 3+ -based compound decreases when temperature increases. This decreasing is not surprising and can be related to the increasing of vibrational-based non-radiative de-excitation. On the opposite, figure 5 evidences that luminescence intensity of the homo-nuclear Tb 3+ -based compound increases when temperature increases. This behavior is quite rare but have already been observed. [START_REF] Lannes | Terbium(III) and yttrium(III) complexes with pyridine-substituted nitronyl nitroxide radical and different beta-diketonate ligands. Crystal structures and magnetic and luminescence properties[END_REF] Estimation Four families of hetero-lanthanide compounds have been synthesized:

[Tb 1-x Gd x (cpbOH)] ∞, [Eu 1-x Gd x (cpbOH)] ∞ , [Tb 1-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 1 and
[Gd 0.2 Tb 0.8-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 0.8. All compounds that constitute these series have been assumed to be iso-structural to [Tb(cpbOH)] ∞ on the basis of their powder diffraction diagrams (Figure S8 to S11). Relative contents of the lanthanide ions have been measured by EDS and they are reported in Table S3. On the basis of previous results obtained on similar systems, [42-43, 52, 76] it has been assumed that lanthanide ions are randomly distributed over the metallic sites of the crystal structure.

In order to estimate the efficiency of intermetallic energy transfers, emission spectra have been measured for all the compounds with general chemical formulas [Tb 1-x Gd x (cpbOH)] ∞ and [Eu 1-x Gd x (cpbOH)] ∞ with 0 ≤ x ≤ 1. Results are reported in Figure 6. For both systems, these measurements are quite different from what is usually observed. [START_REF] Badiane | High britness and easy color modulation in lanthanide-based coordination polymers with 5-methoxyisophthalate as ligand: Toward emission colors additive strategy[END_REF][START_REF] Freslon | Brightness and color tuning in a series of lanthanide-based coordination polymers with benzene 1,2,4,5-tetracarboxylic acid as ligand[END_REF][START_REF] Freslon | Influence of photo-induced electron transfer on lanthanide-based coordination polymers luminescence : A comparison between two pseudo-isoreticular molecular networks[END_REF][START_REF] Fan | Heteronuclear lanthanide-based coordination polymers exhibiting tunable multiple emission spectra[END_REF][START_REF] Haquin | Color and Brightness tuning in heteronuclear lanthanide teraphthalate coordination polymers[END_REF][START_REF] Badiane | Lanthanide based coordination polymers with a 4,5-dichlorophthalate ligand exhibiting highly tunable luminescence : Toward luminescent bar codes[END_REF][START_REF] Luo | Synthesis, Crystal Structure and Luminescent Properties of New Lanthanide-Containing Coordination Polymers Involving 4,4'-oxy-bis-benzoate as Ligand[END_REF] Actually, as Gd 3+ content increases, an abrupt increasing of the luminescence intensity is not observed. This is probably related to the very short inter-metallic distances along the a crystallographic axis (4.3 -5.3 Å). Indeed, inter-metallic energy transfer efficiency highly depends on inter-metallic distance [START_REF] Dexter | A theory of sensitized luminescence in solids[END_REF][START_REF] Förster | Comparative effects of radiation[END_REF] and it has been demonstrated that presence of "dimeric" units induces very efficient inter-metallic energy transfer even when average inter-metallic distance is important. [START_REF] Rodrigues | Tb3+->Eu3+ energy transferin mixed lanthanide organic frameworks[END_REF] On the other hand, luminescence intensity is almost unchanged from x = 0.1 to x = 0.8 which indicates that the decrease of optically active lanthanide ions content (Tb 3+ or Eu 3+ ) is compensated by the diminution of inter-metallic energy transfer. This suggests that inter-metallic energy transfer is strong and that dilution by non-acceptor lanthanide ion (Gd 3+ ) is efficient over a large range of dilution rate. This is in quite good agreement with the fact that, for a given lanthanide ion there are eight lanthanide ions that are closer than 10 Å in the crystal structure.

In order to estimate Tb 3+ -to-Eu 3+ energy transfer, luminescence spectra of [Tb 1-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 1 have been measured (Figure 7). These measurements shows an efficient Tb 3+ -to-Eu 3+ energy transfer as soon as x becomes greater than 0.1. To quantify the efficiency of this inter-metallic transfer ( ET ), luminescence lifetimes of [Tb 1-x Eu x (cpbOH)] ∞ and [Tb 1-x Gd x (cpbOH)] ∞ with 0 ≤ x ≤ 1 have been measured and relationship (1) has been used (See Table 4):

η ET = 1 - τ obs τ 0 ( 1
)
where  obs and  0 are the observed luminescent lifetimes of Tb 3+ in presence ( obs ) and in absence ( 0 ) of an acceptor ion(Eu 3+ ). [START_REF] Eliseeva | Lanthanide luminescence for functionnal materials and biosciences[END_REF] 4 show that inter-metallic energy transfer reaches a plateau for x ≈ 0.2 and then remains almost constant. This quite moderate value of the calculated inter-metallic energy transfer efficiency ( ET ≈ 45%) was unexpected. Indeed, colorimetric coordinates of [Tb 1-x Eu x (cpbOH)] ∞ (Figure 8) evidence a very efficient Tb 3+ -to-Eu 3+ energy transfer that compares well with what was observed in previously reported systems for which  ET was about 90%. [START_REF] Haquin | Color and Brightness tuning in heteronuclear lanthanide teraphthalate coordination polymers[END_REF] This is probably related to the anisotropic character of the metallic distribution in this crystal structure.

In order to estimate the effect of optical dilution in this Eu/Tb system, series of compounds with respective general chemical formulas [Tb 1-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 1 and [Gd 0.2 Tb 0.8-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 0.8 were compared on the basis of their luminance and colorimetric coordinates under UV irradiation, and luminescence spectra (Figure 8). This comparison evidences that dilution by 20% of Gd 3+ ions reduces significantly inter-metallic energy transfer and allows to observe both characteristic emissions of Tb 3+ and Eu 3+ ions under unique UV irradiation. Luminescence spectra of [Tb 0.5 Eu 0.5 (cpbOH)] ∞ were recorded between 77 K and 293 K (Figure 9). Figure 9 shows that I Tb /I Eu ratio can be fitted by two linear relationships with quite good agreement factors: between 77 K and 175 K, I Tb /I Eu = -0.006T + 1.451 (R 2 = 0.985), and between 175 K and room temperature, I Tb /I Eu = -0.0018T + 0.6676 (R 2 = 0.941).

Evaluation of the sensitivity of molecular thermometers is used to be calculated by the following relationship: [START_REF] Cui | Dual emitting MOF-Dye composite for ratiometric temperature sensing[END_REF] S =

∂P ∂T P ( 2
)
where P is the temperature dependent parameter that has been chosen (luminescence intensity, luminescence lifetime or luminescence intensity ratio for instance). [START_REF] Cui | Dual emitting MOF-Dye composite for ratiometric temperature sensing[END_REF][START_REF] Cadiau | Ratiometric nanomether based on an emissive Ln 3+ -organic framework[END_REF] Therefore, in the present case, relationship (2) becomes:

S = ∂(I Tb /I Eu ) ∂T I Tb /I Eu (3)
With this relationship, the maximum sensitivity for this system is 1.18 %.K -1 centered at 130 K in the 77 -300 K temperature range (Figure S17). This value is in agreement with what has previously been reported for other systems. [START_REF] Rocha | Lanthanide organic framework luminescent thermometers[END_REF] However, Figure 9 also evidences that this compound is not optimized as far as thermometer probes are targeted. Indeed, both Eu 3+ and Tb 3+ ions, luminescence intensities decrease as the temperature increases. Moreover, variation of Tb 3+ intensity is moderate and the curve I Tb vs T is almost flat. At last, relative luminescence intensity of Tb 3+ is low (0% < I Tb normalyzed < 6%) which induces a low accuracy of its determination.

To increase I Tb , optically diluted anologous [Gd 0.2 Tb 0.7 Eu 0.1 (cpbOH)] ∞ was synthesized and its emission spectra were recorded between 77 K and room temperature (Figure 10). As expected, I Tb is much greater (45% < I Tb normalyzed < 85%) than in the previous compound. Moreover, luminescence intensity of Tb 3+ and of Eu 3+ do not vary in the same way anymore: as the temperature increases, Eu 3+ luminescence intensity slightly oscillates between 77 K and 300 K with a maximum at 160 K and a minimum at 250 K while the one of Tb 3+ decreases continuously over the whole temperature range. Since inter-metallic energy transfer can be modulated by optical dilution in this system, dual visible and IR emission can be targeted. This is the reason why [Tb 0.95 Nd 0.05 (cpbOH)] ∞ and [Gd 0.20 Tb 0.75 Nd 0.05 (cpbOH)] ∞ have been synthesized (Figure S12 and Table S3). Their luminescence spectra were recorded at room temperature (Figure 11). In both cases, characteristic luminescence of both Tb 3+ and Nd 3+ ions was observed. To the best of our knowledge, this is quite rare because most often, the presence of Nd 3+ provokes a quenching of Tb 3+ luminescence. 5).

These values evidences that dilution by Gd 3+ ions strongly reduces the Tb 3+ -to-Nd 3+ intermetallic energy transfer. Additionally, in order to evaluate the Eu 3+ -to-Nd 3+ energy transfer, the series of compounds with general chemical formula [Eu 1-x Nd x (cpbOH)] ∞ with 0 ≤ x ≤ 1 has been prepared. They are all isostructural to [Tb(cpbOH)] ∞ (Figure S13 and Table S3). Their luminescent properties have been recorded (Figure 12) Indeed, Eu 3+ luminescence abrutly decreases for 0 ≤ x ≤ 0.2. This decreasing is accompagnied by an increasing of Nd 3+ luminescence. This is in agreement with an efficient Eu 3+ -to-Nd 3+ energy transfer. However for x values comprised between 0.2 and 0.8, Nd 3+ luminescence is almost constant. Then it abruptly increases for x values comprised between 0.8 and 1. This behavior was unexpected and suggests a Nd 3+ -to-Eu 3+ energy back tranfer.

On the basis of these results, an isostructural hetero-lanthanide coordination polymer with chemical formula [Gd 0.20 Tb 0.40 Eu 0.25 Nd (cpbOH)] ∞ (Figure S14 and table S3) has been prepared and its solid state luminescent properties have been recorded (Figures 13 andS19). As expected, this compound exhibits sizeable luminescence at room temperature in both the visible and the IR domains (Figure 13). Therefore, it should be possible to use this compound as a multi-gauge thermometer probe. In order to verify this assumption, luminescent properties have been measured in the range 77 K -300 K in both visible and IR domains (Figure 14) and the two luminescence intensity ratios (I Tb /I Eu and I Tb /I Nd ) have been extracted. On the basis of these measurements, it is possible to calculate the sensitivity toward temperature (from relationship (3)) of this compound in different temperature ranges (Table 6 and Figures S20 andS21). It can also be noticed that comparison between figures 5, 9 10 and 14 evidences that in this system, inter-metallic energy transfer is strongly dependent of the temperature and the system composition (Figure 15).

CONCLUSIONS AND OUTLOOKS.

Compounds that are described in this paper present strong inter-metallic energy transfers and quite intense and temperature dependent emissions for Tb 3+ , Eu 3+ and Nd 3+ ions.

The anisotropic nature of the metallic distribution in the material makes the optical dilution by Gd 3+ ions efficient. Indeed, multiple emissions are achievable for 20% Gd 3+ content. These results demonstrate that it is possible to modulate inter-metallic energy transfer and to design compounds that emit, under a unique excitation wavelength, in both visible and infra-red regions.

Efficiency of these not optimized compounds is far from the one exhibited by some previously reported systems. [START_REF] Brites | Lanthanide-based luminescent molecular thermometers[END_REF][START_REF] Rocha | Lanthanide organic framework luminescent thermometers[END_REF] However, to the best of our knowledge these compounds constitute the first example of potential multi-gauge thermometric probes based on multi-emission. [START_REF] Rocha | Lanthanide organic framework luminescent thermometers[END_REF] ACKNOWLEDGEMENT.

The

  -lanthanide based coordination polymers were obtained by mixing stoichiometric amounts of a lanthanide chloride and the sodium salt of 1,4-carboxyphenylboronic acid in water under ambient pressure and temperature. Precipitation immediately occurred. Precipitates were filtered, rinsed with water and dry in air. The yields were close to 90%. On the basis of their powder X-ray diffraction diagrams, microcrystalline powders were classified in two families of isostructural compounds depending on the involved lanthanide ion (Figure S7): compounds with general chemical formula [Ln(cpb) 3 (H 2 O) 2 ] ∞ (hereafter abbreviated as [Ln(cpb) 3 ] ∞ ) were obtained for Ln = La or Ce, while for Ln = Pr-Lu (except Pm) plus Y, compounds have general chemical formula

x

   , y  , z  trichromatic values x = X/(X+Y+Z), y = Y/(X+Y+Z) and z = Z/(X+Y+Z). Mean xyz values are given for each sample, which act as light sources (luminescent samples). Standards from Phosphor Technology were used for calibration at 312 nm: red phosphor Gd 2 O 2 S:Eu (x = 0.667, y = 0.330) and green phosphor Gd 2 O 2 S:Tb (x = 0.328, y = 0.537).

  double-chains molecular motifs that spread along the b axis. Molecular motifs are held together by a strong hydrogen-bonds network that involves -OH groups of the boronic functions (d O-O ≈ 2.77 Å) in one hand and the coordination water molecules (d O-O = 2.84 Å) in the other hand (Figure 1).

Figure 1 .

 1 Figure 1. Projection view along the b axis of an extended unit cell of [La(cpb) 3 ] ∞ .

Figure 2 .

 2 Figure 2. Perspective view along the b axis of a double-chains molecular motif in [La(cpb) 3 ] ∞ . In inset, coordination mode of the cpb -ligands in [La(cpb) 3 ] ∞ .

Figure 3 .

 3 Figure 3. Top: Projection view along the b axis of the crystal packing of [Tb(cpbOH)] ∞ . Shortest intermetallic distances between lanthanide ions that belong to different wavy planes are reported. Bottom: Projection view along the c axis of a molecular wavy plane in [Tb(cpbOH)] ∞ . Shortest intermetallic distances are reported. This compound crystallizes in the orthorhombic system, space group Pbca (n°61) with a = 8.5704(1) Å, b = 19.5441(1) Å and c = 21.4191 Å (CCDC-962513). Redrawn from reference 48.

However, Scheme 2 shows that the 9 . 5 ÅScheme 2 . 1 =

 9521 Scheme 2. Representation of the neighborhood of a given lanthanide ion (in yellow). Lanthanide ions that are closer than 10 Å from that given lanthanide ion, are in blue. Dotted line represents the projection of a virtual sphere centered on the given lanthanide ion (in yellow) and with a 10 Å radius.

Figure 4 .

 4 Figure 4. Solid state excitation and emission spectra of [Ln(cpbOH)] ∞ with Ln = Nd(III), Eu(III) or Tb(III) at 293 K.

Figure 5 .

 5 Figure 5. Left: Luminescence spectra versus temperature of [Ln(cpbOH))] ∞ with Ln = Nd (Top), Eu (Middle) or Tb (Bottom).  exc = 302 nm. Right: Integrated intensity I Ln versus T for the three compounds.

  of the inter-metallic energy transfer efficiency: Emission in the visible region of hetero-lanthanide coordination polymers, [Tb 1-x Gd x (cpbOH)] ∞, [Eu 1-x Gd x (cpbOH)] ∞ , [Tb 1-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 1 and [Gd 0.2 Tb 0.8-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 0.8.

Figure 6 .

 6 Figure 6. Luminescence spectra of [Tb 1-x Gd x (cpbOH)] ∞ (left) and of [Eu 1-x Gd x (cpbOH)] ∞ (right) with 0 ≤ x ≤ 1 versus x ( exc = 303 nm) at 293 K. In insets, integrated intensities of the major characteristic emission peaks of Tb 3+ centered at 545 nm ( 5 D 4 → 7 F 5 ) (left) and of Eu 3+ centered at 611.5 nm ( 5 D 0 → 7 F 2 ) (right) versus x.

Figure 7 .

 7 Figure 7. Left: Luminescence spectra of [Tb Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 1 versus x ( exc = 303 nm) at 293 K. Right: integrated intensities of the major characteristic emission peaks of Tb 3+ and Eu 3+ centered at 545 nm ( 5 D 4 → 7 F 5 ) and 612 nm ( 5 D 0 → 7 F 2 ) respectively versus x.

Figure 7

 7 Figure 7 and Table4show that inter-metallic energy transfer reaches a plateau for

Figure 8 .

 8 Figure 8. Colorimetric coordinates, luminescence spectra ( exc = 303 nm) and luminance versus x under UV irradiation of [Tb 1-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 1 (Top) and of [Gd 0.2 Tb 0.8-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 0.8 (Bottom).

Figure 9 .

 9 Figure 9. Left: Luminescence spectra of [Tb 0.5 Eu 0.5 (cpbOH)] ∞ ( exc = 305 nm) between 77 and 293 K. Right: Relative intensities of Tb 3+ (I Tb ) and Eu 3+ (I Eu ) and the ratio I Tb /I Eu vs temperature.

Figure 10 .

 10 Figure 10. Luminescence spectra of [Gd 0.2 Tb 0.7 Eu 0.1 (cpbOH)] ∞ ( exc = 302 nm) between 77 and 300 K (left). Relative intensities of Tb 3+ (I Tb ) and Eu 3+ (I Eu ) and the ratio I Tb /I Eu vs temperature (right).

Figure 11 .

 11 Figure 11. Solid state excitation and emission spectra of [Tb 0.95 Nd 0.05 (cpbOH)] ∞ (Top) and of [Gd 0.2 Tb 0.75 Nd 0.05 (cpbOH)] ∞ (Bottom) at 293 K.

Figure 12 .

 12 Figure 12. Luminescence spectra of [Eu 1-x Nd x (cpbOH)] ∞ with 0 ≤ x ≤ 1 versus x ( exc = 303 nm) at 293 K. In inset, integrated intensities of the major characteristic emission peaks of Eu 3+ and Nd 3+ centered at 611.5 nm ( 5 D 0  7 F 2 ) and 1055 nm ( 4 F 3/2  4 I 11/2 ) respectively versus x.

Figure 12

 12 Figure12evidences a complex competition between energy transfer mechanisms.

Figure 13 .

 13 Figure 13. Solid state excitation and emission spectra of [Gd 0.20 Tb 0.40 Eu 0.25 Nd 0.15 (cpbOH)] ∞ at 293 K.  obs (Tb) = 0.35(1) ms and  obs (Eu) = 0.17(1) ms at 293K.

Figure 14 .

 14 Figure 14. Solid state luminescence of [Gd 0.20 Tb 0.40 Eu 0.25 Nd 0.15 (cpbOH)] ∞ versus temperature in both visible (Top left) and IR (Top right) regions in the 77 K -300 K temperature range. Tb(III), Eu(III) and Nd(III) relative luminescence intensity (Bottom left) and luminescence intensity ratios (Bottom right) versus temperature between 77 K and 300 K. I /I Eu vs T (Dark circles) and I Tb /I Nd vs T (Blue squares). obs (Tb) = 0.45(1) ms and  obs (Eu) = 0.22(1) ms at 77 K.

Figure 15 .

 15 Figure 15. Tb(III) normalized luminescence intensities in [Tb(cpbOH)] ∞ , [Tb 0.5 Eu 0.5 (cpbOH)] ∞ , [Gd 0.2 Tb 0.7 Eu 0.1 (cpbOH)] ∞ and [Gd 0.20 Tb 0.40 Eu 0.25 Nd 0.15 (cpbOH)] ∞ .

  China Scholarship Council Ph.D. Program, a cooperation program with the French UT & INSA, is acknowledged for financial support. SUPPORTING INFORMATION. Crystal and final structure refinement data for Hcpb•0.25H 2 O; Projection views of the asymmetric units and of the crystal packing of Hcpb•0.25H 2 O; Experimental diagram of commercial Hcpb; TG/DSC analysis of Hcpb; TG/DSC analyses of Nacpb•1.5H 2 O; Extended asymmetric unit of Nacpb•2H 2 O; Crystal and final structure refinement data for Nacpb•2H 2 O; Experimental powder X-ray diffraction diagrams of homo-lanthanide-based coordination polymers with 4-carboxyphenylboronic acid as ligand; Metallic relative contents in hetero-lanthanide compounds; Experimental powder X-ray diffraction diagrams of [Tb 1- x Gd x (cpbOH)] ∞ with 0 ≤ x ≤ 1, [Eu 1-x Gd x (cpbOH)] ∞ with 0 ≤ x ≤ 1, [Tb 1-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 1, [Gd 0.2 Tb 0.8-x Eu x (cpbOH)] ∞ with 0 ≤ x ≤ 1, [Gd 0.20 Tb 0.40 Eu 0.25 Nd 0.15 (cpbOH)] ∞ , [Gd 0.20 Tb 0.75 Nd 0.05 (cpbOH)] ∞ and [Tb 0.95 Nd 0.05 (cpbOH)] ∞ , [Eu 1-x Nd x (cpbOH)] ∞ with 0 ≤ x ≤ 1, [Gd 0.20 Tb 0.40 Eu 0.25 Nd 0.15 (cpbOH)] ∞ ; Solid state excitation and emission spectra of [Gd(cpbOH)] ∞ at 77 K; Solid state excitation and emission spectra of [Ln(cpbOH)] ∞ with Ln = Sm(III), Dy(III) or Ho(III); Thermometric parameters calculations of [Tb 0.5 Eu 0.5 (cpbOH)] ∞ , [Gd 0.2 Tb 0.7 Eu 0.1 (cpbOH)] ∞ and [Gd 0.20 Tb 0.40 Eu 0.25 Nd 0.15 (cpbOH)] ∞ ; Solid state emission spectra vs excitation wavelength (λ exc = 295 -400 nm) of [Gd 0.20 Tb 0.40 Eu 0.25 Nd 0.15 (cpbOH)] ∞ at 293 K.

Table 1 .

 1 Cell parameters for Hcpb•nH 2 O with n = 0, 1 or 0.25

		Hcpb	Hcpb•H 2 O	Hcpb•0.25H 2 O	Hcpb•0.25H 2 O
	reference	50	50	50	This work
	formula	C 7 H 7 BO 4	C 7 H 9 BO 5	C 7 H 7.5 BO 4.25	C 7 H 7.5 BO 4.25
	system	monoclinic	orthorhombic	orthorhombic	monoclinic
	space group (n°)	C2/c (15)	Ccc2 (37)	Fddd (70)	C2/c (15)
	a (Å)	11.378(5)	7.566(5)	13.140(3)	18.226(2)
	b (Å	9.825(5)	11.929(7)	18.138(5)	13.2209(17)
	c (Å)	7.245(3)	9.769(6)	25.328(7)	15.6353(17)
	 (°)	120.08(7)	-	-	125.655(3)
	V (Å 3 )	700.8(6)	881.7(9)	6037(3)	3061.3(6)
	Z	4	4	32	16

Table 2 .

 2 Crystal and final structure refinement data for [La(cpb) 3 ] ∞

	1,4-carboxyphenylboronic lead to two families of isostructural compounds depending on the
	involved lanthanide ion: [Ln(cpb) 3 ] ∞ with Ln = La-Ce and [Ln(cpbOH)] ∞ with Ln = Pr-Lu
	(except Pm) plus Y (Figure S7).
	Crystal structures of [Ln(cpb) 3 ] ∞ with Ln = La-Ce.
	La 3+ -and Ce 3+ -based coordination polymers have general abbreviated chemical
	formula [Ln(cpb) 3 ] Molecular formula	La 1 C 21 H 22 B 3 O 14
	System	monoclinic
	Space group (No.)	P2 1 /n (14)
	a (Å)	22.7993(5)
	b (Å)	5.2334(1)
	c (Å)	23.2460(6)
	β (°)	118.608(1)
	V (Å 3 )	2435.04(10)
	Z	4
	Formula weight (g.mol -1 )	669.73
	D calc (g.cm -3 ) µ (mm -1 )	1.827 1.828
	R (%)	4.63
	R W (%)	11.80
	GoF	1.230
	N° CCDC	962509

∞ where Ln = La or Ce. Crystal structure has been solved on the basis of the lanthanum-containing derivative. Crystal and final structure refinement data of the crystal structure are listed in Table

2

.

Table 3 .

 3 Overall luminescent quantum yields and observed lifetime for [Ln(cpbOH)] ∞ with Ln = Eu and Tb

	Q Ln 3+ Ligand (%)	 obs (ms)

Solid state luminescence versus temperature of [Ln(cpbOH)] ∞ with Ln = Nd, Eu or Tb.

Table 4 .

 4 Observed lifetimes for [Tb 1-x Eu x (cpbOH)] ∞ and [Tb 1-x Gd x (cpbOH)] ∞ for 0 ≤ x ≤ 1

		[Tb 1-x Gd x (cpbOH)] ∞
	x =	0	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1
	τ Tb * = τ 0 (ms)	0.83	0.86	0.85	0.85	0.85	0.85	0.85	0.86	0.86	0.86	n/a
		[Tb 1-x Eu x (cpbOH)] ∞
	x =	0	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1
	τ Tb * = τ obs (ms) 0.83	0.57	0.50	0.45	0.43	0.50	0.49	0.48	0.45	0.40	n/a
	τ Eu * (ms)	n/a	0.30	0.26	0.25	0.27	0.27	0.27	0.27	0.27	0.27	0.27
	η ET * (%)	n/a	33	41	47	49	42	43	43	48	54	n/a

* uncertainties on the measurements are evaluated to 5%

Table 5 .

 5 Luminescence lifetimes of the Tb 3+ ion for [Tb 0.95 Gd 0.05 (cpbOH))] ∞ , [Tb 0.95 Nd 0.05 (cpbOH)] ∞ , [Gd 0.2 Tb 0.8 (cpbOH)] ∞ and [Gd 0.2 Tb 0.75 Nd 0.05 (cpbOH)] ∞

	Chemical formula

Table 6 .

 6 Luminescence of [Gd 0.20 Tb 0.40 Eu 0.25 Nd 0.15 (cpbOH)] ∞ versus temperature. Linear function and thermometric sensitivities vs temperature range

	I Ln /I Ln'	Linear function temperature range (K)	Linear function T = f(I Ln /I Ln' )	Sensitivities temperature range (K)	Maximum sensitivities S (%.K -1 )
		77 -180	-0.0045T + 1.3513 (R 2 = 0.99)
	I Tb /I Eu	180 -300	-0.0011T + 0.7272 (R 2 = 0.89)	77 -300	0.63 at 110 K
	I Tb /I Nd	77 -300	-0.0018T + 1.0852 (R 2 = 0.92)	77 -300	0.29 at 180 K

Table 6

 6 evidences that multi-emissive materials can present different sensitivities in different temperature ranges. This could be of interest as far as accurate temperature measurements would be needed over a large temperature range or with host matrix that present dark optical zones.

Reactions in water of lanthanide chlorides with the sodium salt of 1,4-carboxyphenyl boronic acid lead to multi-emissive lanthanide-based coordination polymers that could find their application as multi-gauge luminescent thermometric probes.