Félix Boussoufi

Marc Pousthomis

Alexis Kuntzmann

Michele D ' Amico

Gilles Patriarche

Benoit Dubertret

Spray-Drying Polymer Encapsulation of CsPbBr 3 Perovskite Nanocrystals with Enhanced Photo-Stability for LED DownConverters

Keywords: CsPbBr3 perovskite nanocrystals, spray-drying, encapsulation, polymer, composite, LED down-converter, photo-stability

Lead halide perovskite nanocrystals (LHP NCs) exhibit remarkable optical and optoelectronical properties but greatly suffer from poor stability in standard ambient and in-use conditions. These stability issues hinder their utilization in many technological applications and in their integration within industrial processes. Herein, we report a polymeric nano-encapsulation method of these NCs based on a spray-drying process, with the aim of using them as light down-converting materials in LED devices. CsPbBr3 NCs were encapsulated in acrylate-based polymers to form NCs / polymer nano-composite beads, with an average diameter lower than 500 nm. Structural and optical characterizations demonstrated good preservation of the NC properties after the spraydrying despite quite harsh process conditions. Specific acrylate-based polymers were selected in order to match native surface ligands from our NCs. This was necessary to obtain an effective encapsulation within the beads. To evaluate the encapsulated NCs photostability under in-use conditions, bare NCs and encapsulated NCs were deposited on the chip of a blue LED down-converter to compare their luminescence stability. We observed that under continuous blue photon excitation, the NCs / polymer nano-composite beads exhibit a much better resistance to photobleaching compared to bare NCs.

INTRODUCTION

Colloidal lead halide perovskite semiconductor nanocrystals (LHP NCs) have attracted much interest since their first hot-injection synthesis reported in 2015. [START_REF] Protesescu | Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut[END_REF] LHP NCs exhibit remarkable optical properties: their photoluminescence quantum yield (PLQY) can reach near unity, they possess a narrow emission spectrum which is tunable over the visible spectrum, and have demonstrated great potential for unique photon sources. [START_REF] Shamsi | Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties[END_REF] Owing to their intrinsic defect tolerance and ease of synthesis, LHP NCs have been employed in many fields of applications, such as light-emitting diodes (LEDs), [START_REF] Congreve | Tunable Light-Emitting Diodes Utilizing Quantum-Confined Layered Perovskite Emitters[END_REF][START_REF] Dong | Bipolar-Shell Resurfacing for Blue LEDs Based on Strongly Confined Perovskite Quantum Dots[END_REF][START_REF] Meyns | Polymer-Enhanced Stability of Inorganic Perovskite Nanocrystals and Their Application in Color Conversion LEDs[END_REF] solar cells, [START_REF] Zhou | Cerium and Ytterbium Codoped Halide Perovskite Quantum Dots: A Novel and Efficient Downconverter for Improving the Performance of Silicon Solar Cells[END_REF][START_REF] Akkerman | Strongly Emissive Perovskite Nanocrystal Inks for High-Voltage Solar Cells[END_REF] cell imaging, [START_REF] Zhang | Embedding Perovskite Nanocrystals into a Polymer Matrix for Tunable Luminescence Probes in Cell Imaging[END_REF][START_REF] Wei | Enhancing the Stability of Perovskite Quantum Dots by Encapsulation in Crosslinked Polystyrene Beads via a Swelling-Shrinking Strategy toward Superior Water Resistance[END_REF] single photon emitters, [START_REF] Tamarat | The Dark Exciton Ground State Promotes Photon-Pair Emission in Individual Perovskite Nanocrystals[END_REF][START_REF] Pierini | Highly Photostable Perovskite Nanocubes: Toward Integrated Single Photon Sources Based on Tapered Nanofibers[END_REF] and security bar codes. [START_REF] Zhang | Conversion of Invisible Metal-Organic Frameworks to Luminescent Perovskite Nanocrystals for Confidential Information Encryption and Decryption[END_REF][START_REF] Yakunin | Radiative Lifetime-Encoded Unicolour Security Tags Using Perovskite Nanocrystals[END_REF] However, LHP NCs suffer from poor stability due to their low formation energy and strong ionic nature. [START_REF] Parobek | Photoinduced Anion Exchange in Cesium Lead Halide Perovskite Nanocrystals[END_REF][START_REF] Dang | In Situ Transmission Electron Microscopy Study of Electron Beam-Induced Transformations in Colloidal Cesium Lead Halide Perovskite Nanocrystals[END_REF] Particularly, the luminescent properties of LHP rapidly degrade in solid-state under ambient conditions, i.e. in presence of oxygen and moisture, or under in-use conditions with heat or light stress, [START_REF] Huang | Lead Halide Perovskite Nanocrystals in the Research Spotlight: Stability and Defect Tolerance[END_REF][START_REF] Yang | Surface Chemistry of All Inorganic Halide Perovskite Nanocrystals: Passivation Mechanism and Stability[END_REF][START_REF] Huang | Morphology Evolution and Degradation of CsPbBr3 Nanocrystals under Blue Light-Emitting Diode Illumination[END_REF][START_REF] Dutta | Annealing CsPbX3 (X = Cl and Br) Perovskite Nanocrystals at High Reaction Temperatures: Phase Change and Its Prevention[END_REF] limiting their potential integration in devices at the industrial scale.

Since their discovery, tremendous efforts have been made to stabilize the properties of LHP NCs. Various studies have been conducted on the chemical stabilization of the LHP NCs, by ligand engineering, [START_REF] Li | Postsynthetic Surface Trap Removal of CsPbX3 (X = Cl, Br, or I) Quantum Dots via a ZnX2 /Hexane Solution toward an Enhanced Luminescence Quantum Yield[END_REF][START_REF] Bodnarchuk | Rationalizing and Controlling the Surface Structure and Electronic Passivation of Cesium Lead Halide Nanocrystals[END_REF][START_REF] Krieg | Stable Ultraconcentrated and Ultradilute Colloids of CsPbX3 (X = Cl, Br) Nanocrystals Using Natural Lecithin as a Capping Ligand[END_REF] or by synthetization of core/shell heterostructures. [START_REF] Shi | Core-Shell CsPbBr 3 @CdS Quantum Dots with Enhanced Stability and Photoluminescence Quantum Yields for Optoelectronic Devices[END_REF][START_REF] Ravi | CsPbBr3/ZnS Core/Shell Type Nanocrystals for Enhancing Luminescence Lifetime and Water Stability[END_REF] These routes effectively led to better stability in solution, but still lack of promising results in the solid-state. Different materials were also explored as host matrices to encapsulate and protect LHPs NCs from external stresses, such as polymers. [START_REF] Meyns | Polymer-Enhanced Stability of Inorganic Perovskite Nanocrystals and Their Application in Color Conversion LEDs[END_REF][START_REF] Wei | Enhancing the Stability of Perovskite Quantum Dots by Encapsulation in Crosslinked Polystyrene Beads via a Swelling-Shrinking Strategy toward Superior Water Resistance[END_REF][START_REF] Raja | Encapsulation of Perovskite Nanocrystals into Macroscale Polymer Matrices: Enhanced Stability and Polarization[END_REF][START_REF] Hai | Designing of Blue, Green, and Red CsPbX3 Perovskite-Codoped Flexible Films with Water Resistant Property and Elimination of Anion-Exchange for Tunable White Light Emission[END_REF][START_REF] Pan | General Strategy for the Preparation of Stable Luminous Nanocomposite Inks Using Chemically Addressable CsPbX3 Peroskite Nanocrystals[END_REF][START_REF] Xin | Highly Stable and Luminescent Perovskite-Polymer Composites from a Convenient and Universal Strategy[END_REF][START_REF] Lin | Water-Resistant Efficient Stretchable Perovskite-Embedded Fiber Membranes for Light-Emitting Diodes[END_REF][START_REF] Tong | Direct Hot-Injection Synthesis of Lead Halide Perovskite Nanocubes in Acrylic Monomers for Ultrastable and Bright Nanocrystal-Polymer Composite Films[END_REF][START_REF] Papagiorgis | Robust Hydrophobic and Hydrophilic Polymer Fibers Sensitized by Inorganic and Hybrid Lead Halide Perovskite Nanocrystal Emitters[END_REF][START_REF] Rainò | Underestimated Effect of a Polymer Matrix on the Light Emission of Single CsPbBr3 Nanocrystals[END_REF][START_REF] Gandini | Fast and Reabsorption-Free Perovskite Nanocrystal-Based Sensitized Plastic Scintillators[END_REF][START_REF] Lu | Composite Films of CsPbBr3 Perovskite Nanocrystals in a Hydrophobic Fluoropolymer for Temperature Imaging in Digital Microfluidics[END_REF] , metal oxides, [START_REF] Huang | Enhancing the Stability of CH3NH3PbBr3 Quantum Dots by Embedding in Silica Spheres Derived from Tetramethyl Orthosilicate in "Waterless" Toluene[END_REF][START_REF] Li | Highly Luminescent and Ultrastable CsPbBr3 Perovskite Quantum Dots Incorporated into a Silica/Alumina Monolith[END_REF][START_REF] Li | Water-Resistant Perovskite Nanodots Enable Robust Two-Photon Lasing in Aqueous Environment[END_REF][START_REF] Zhang | Ceramic-like Stable CsPbBr3 Nanocrystals Encapsulated in Silica Derived from Molecular Sieve Templates[END_REF] metallic salt, [START_REF] Dirin | Microcarrier-Assisted Inorganic Shelling of Lead Halide Perovskite Nanocrystals[END_REF] metal organic frameworks, [START_REF] Zhang | Conversion of Invisible Metal-Organic Frameworks to Luminescent Perovskite Nanocrystals for Confidential Information Encryption and Decryption[END_REF][START_REF] Cha | Formation and Encapsulation of All-Inorganic Lead Halide Perovskites at Room Temperature in Metal-Organic Frameworks[END_REF] or graphene/2D materials, [START_REF] Huang | In Situ Growth of All-Inorganic Perovskite Nanocrystals on Black Phosphorus Nanosheets[END_REF][START_REF] Li | Ultrafast Interfacial Energy Transfer and Interlayer Excitons in the Monolayer WS2 /CsPbBr3 Quantum Dot Heterostructure[END_REF] . LHP NCs / polymers composite films were the first materials to be tested, thanks to the simplicity and the soft conditions of polymer processability which suite well to the poor stability of LHP NCs. For example, in 2016, Raja. et al. formed micron thick composite films by simply blending CsPbBr3 NCs and high-molecular-weight polymers such as polystyrene and acrylate-based polymers. [START_REF] Raja | Encapsulation of Perovskite Nanocrystals into Macroscale Polymer Matrices: Enhanced Stability and Polarization[END_REF] More recently, Lu et al. used a hydrophobic fluoropolymer to form 100 nm thick composite films with the same blending method, reaching a high stability in water for temperature imaging in digital microfluidics. [START_REF] Lu | Composite Films of CsPbBr3 Perovskite Nanocrystals in a Hydrophobic Fluoropolymer for Temperature Imaging in Digital Microfluidics[END_REF] In situ polymerization was also studied, [START_REF] Pan | General Strategy for the Preparation of Stable Luminous Nanocomposite Inks Using Chemically Addressable CsPbX3 Peroskite Nanocrystals[END_REF][START_REF] Xin | Highly Stable and Luminescent Perovskite-Polymer Composites from a Convenient and Universal Strategy[END_REF][START_REF] Tong | Direct Hot-Injection Synthesis of Lead Halide Perovskite Nanocubes in Acrylic Monomers for Ultrastable and Bright Nanocrystal-Polymer Composite Films[END_REF][START_REF] Gandini | Fast and Reabsorption-Free Perovskite Nanocrystal-Based Sensitized Plastic Scintillators[END_REF] for example Tong et al. developed an ultraviolet polymerization after a blade coating of a mixture of CsPbBr3 NCs; using monomers as both ligands and solvent, the obtained films showed promising photostability against continuous illumination. [START_REF] Tong | Direct Hot-Injection Synthesis of Lead Halide Perovskite Nanocubes in Acrylic Monomers for Ultrastable and Bright Nanocrystal-Polymer Composite Films[END_REF] Even if remarkable stability improvements have been made in the past few years for composite NCs / polymeric films, these macroscopic encapsulation approaches are only tailored to a few applications, mainly for optoelectronic devices. Instead of embedding NCs in macroscopic matrices, another approach consists of forming micro-or nano-composite polymeric particles. These composite particles present several advantages ranging from their ability to be dispersed and incorporated in media or other matrices, simplified handling, and additional surface functionalization is possible. Until now, different methods have been developed to form polymeric beads with fluorescent NCs inside, including: swelling/shrinking methods, [START_REF] Wei | Enhancing the Stability of Perovskite Quantum Dots by Encapsulation in Crosslinked Polystyrene Beads via a Swelling-Shrinking Strategy toward Superior Water Resistance[END_REF][START_REF] Bradley | Distribution of CdSe Quantum Dots within Swollen Polystyrene Microgel Particles Using Confocal Microscopy[END_REF] suspension polymerization, [START_REF] Vaidya | Reduction in Aggregation and Energy Transfer of Quantum Dots Incorporated in Polystyrene Beads by Kinetic Entrapment Due to Cross-Linking during Polymerization[END_REF][START_REF] O'brien | Quantum Dot-Labelled Polymer Beads by Suspension Polymerisation[END_REF] electro-spray, [START_REF] Koekoekx | Electrospraying the Triblock Copolymer SEBS: The Effect of Solvent System and the Embedding of Quantum Dots[END_REF] or microfluidic jet-mode breakup. [START_REF] Lee | High Throughput Synthesis of Uniform Biocompatible Polymer Beads with High Quantum Dot Loading Using Microfluidic Jet-Mode Breakup[END_REF] For LHP NCs, Wei et al. have formed CsPbBr3 NCs / polystyrene nano-and micro-composite beads by a swelling/shrinking strategy with superior waterresistant properties. Similar approaches have also been developed for nanocomposite LHP NCs / polymers microcomposite fibers. [START_REF] Lin | Water-Resistant Efficient Stretchable Perovskite-Embedded Fiber Membranes for Light-Emitting Diodes[END_REF][START_REF] Papagiorgis | Robust Hydrophobic and Hydrophilic Polymer Fibers Sensitized by Inorganic and Hybrid Lead Halide Perovskite Nanocrystal Emitters[END_REF] Despite these notable advancements, there is always a need for effective and scalable methods to produce LHP NCs / polymer nano-composite particles. Furthermore, a deeper study of their photo-stability is needed to evaluate their performance and determine their potential as light down-converting materials in LED applications. To achieve this objective whilst proposing a new approach for the fabrication of nano-composite particles with improved stability, we wanted to explore the utilization of a spray-drying method to encapsulate LHP NCs in polymeric beads. This process has been known since the late 19 th century [START_REF] Percy | Improvement in Drying and Concentrating of Liquid Substances by Atomizing[END_REF] and is currently a cost-effective, facile, and scalable process. [START_REF] Sosnik | Advantages and Challenges of the Spray-Drying Technology for the Production of Pure Drug Particles and Drug-Loaded Polymeric Carriers[END_REF] The spray-drying process is widely used in the pharmaceutical, flavor, and food industries. The adoption of this technique is widespread as it permits manufacturers to produce a dry powder from a solution of chemical components by atomization into small droplets dried in a hot zone to obtain solid beads. [START_REF] Sosnik | Advantages and Challenges of the Spray-Drying Technology for the Production of Pure Drug Particles and Drug-Loaded Polymeric Carriers[END_REF]50 This technique can serve to simply dry active substances or to encapsulate target molecules, such as drugloaded carrier systems. 50,[START_REF] Azad | Spray Drying of Drug-Swellable Dispersant Suspensions for Preparation of Fast-Dissolving, High Drug-Loaded, Surfactant-Free Nanocomposites[END_REF][START_REF] Sun-Waterhouse | Spray-Drying Microencapsulation of Polyphenol Bioactives: A Comparative Study Using Different Natural Fibre Polymers as Encapsulants[END_REF] Because spray-drying is suited to sensitive components thanks to its fast drying step (few milliseconds), it seemed interesting to us to encapsulate LHP NCs with this process and measure the potential stability improvements. To the best of our knowledge, only one similar combination had been reported in 2006 by Chu et al., who successfully incorporated CdTe quantum dots in bovine serum albumin for bio medical applications, but the final photostability of their micro-composite beads was not evaluated. [START_REF] Chu | Incorporating Quantum Dots into Polymer Microspheres via a Spray-Drying and Thermal-Denaturizing Approach[END_REF] Herein, we report an effective encapsulation method based on a spray-drying process, to produce CsPbBr3 NCs / polymers nano-composite beads. We employed acrylate-based polymers and managed to obtain beads within a fine range of drying temperatures. We performed morphological, structural, and optical characterization on the composite beads. The influence of the NCs surface ligands on the encapsulation was of paramount importance, since we show that only CsPbBr3 NCs with short native ligands were properly encapsulated within the polymeric beads. Spray-dried CsPbBr3 NCs conserved their initial structural properties while the PLQY was much better preserved at solid-state compare to films of bare NCs. The photo-stability of NCs / polymer nano-composite beads was studied using a LED down-converter device with "NCs onchip" deposition. We measured an improved NCs photostability with the spray-drying encapsulation, resulting in a stable green emission that was recorded after 200 h of continuous photon excitation.

RESULTS AND DISCUSSION

Because NC surface ligands and polymer matrix interactions play an important role in NC dispersion, [START_REF] Li | Ligand Engineering of Polymer Nanocomposites: From the Simple to the Complex[END_REF] two syntheses of CsPbBr3 NCs with different surface ligands were studied to develop the spray-drying polymer encapsulation. First, CsPbBr3 NCs with long ligands (CsPbBr3-LL) were synthesized following a classical hot-injection synthesis based on the protocol developed by Protesescu et al., [START_REF] Protesescu | Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut[END_REF] where oleic acid and oleylamine play the role of long alkyl chain stabilizers.

Second, CsPbBr3 NCs with short ligands (CsPbBr3-SL) were synthesized following a room-temperature synthesis based on the protocol developed by Akkerman et al., [START_REF] Akkerman | Strongly Emissive Perovskite Nanocrystal Inks for High-Voltage Solar Cells[END_REF] with propionic acid and butylamine as stabilizers. As shown in Figure 1a and 1b, CsPbBr3-LL NCs exhibited a cubic shape with an average lateral dimension of 9.1 ± 1.3 nm according to HAADF-STEM images, whereas CsPbBr3-SL NCs exhibited crystalline domains of 19.6 ± 6.1 nm in size, revealing higher size dispersity for the short ligand synthesis. Moreover, while CsPbBr3-LL NCs were well separated from each other on the TEM grid due to the presence of long organic ligands, CsPbBr3-SL NCs were agglomerated since short ligands cannot maintain a steric barrier between NCs. Analyses of high-resolution STEM images confirmed that both types of NCs crystallized in the orthorhombic crystalline structure of CsPbBr3 perovskite (Figure S1 andS2). The optical properties of the NCs are shown in Figure 1c. The CsPbBr3-SL NCs absorbance spectrum illustrates the presence of light scattering, a phenomenon mainly due to the poor colloidal stability of the NCs, since short ligands induced weaker steric barriers than long ligands. [START_REF] De Roo | Highly Dynamic Ligand Binding and Light Absorption Coefficient of Cesium Lead Bromide Perovskite Nanocrystals[END_REF] This difference of colloidal stability was clearly identified by the turbidity of the suspension of CsPbBr3-SL NCs after synthesis and purification (Figure S3). The photoluminescence (PL) spectra showed an emission peak centered at 517 and 520 nm for CsPbBr3-LL and CsPbBr3-SL NCs respectively, with a full width at half maximum (FWHM) of 18 and 22 nm, respectively. The absolute PLQY was measured at 70-80 % for CsPbBr3-LL NCs and 60-70 % for CsPbBr3-SL NCs, depending on the synthesis batch.

Figure 2 shows a sketch of the spray-drying process for nano-encapsulation of CsPbBr3 NCs within polymeric beads. The initial solution feed was composed of CsPbBr3 NCs and a specific formulation of polymer dissolved in toluene at 4 wt%. Toluene was used as the solvent because of its good compatibility with LHP NCs and its capability to dissolve many commercial hydrophobic polymers. The spray-drying process can be divided into three main steps. The first step involves the atomization of the solution feed into micrometric droplets. In the second step, these solvent droplets containing the solubilized polymeric chains and CsPbBr3 NCs were pulled along the glass tube by a nitrogen flow and then dried in a hot zone heated by a tubular furnace in the range of 170-290 °C. At this stage, the solvent was quickly evaporated, and the polymer condensed into a spherical shape that encapsulated the NCs. In the last step, the resulting dried polymeric beads containing CsPbBr3 NCs were collected on a filter. The encapsulation process is very rapid, taking less than 1 second between the first droplet formation and the first dried beads collected on the final filter. We measured a material yield around 50 %, corresponding to the weight ratio between the initial compounds (polymers + NCs) and the final beads weight collected on the filter. Most of the material loss was due to the dried polymer that remained stuck on the inner glass tube surface. This materials loss is intrinsic to the small-scale spraydrying setup used in this study, higher material yield is expected when using an industrial scale spray-dryer.

Different hydrophobic polymers were tested and each one was evaluated through three main criteria: to obtain solid polymeric beads, to retain the CsPbBr3 NC photoluminescence properties, and to get an homogeneous NCs dispersion within the beads. In this work, we will only discuss the polymeric formulation with 50:50 in weight of poly(methyl methacrylate) (PMMA) and poly(butyl methacrylate-co-methyl methacrylate) (PBMMA) as it led to the best results among the different formulations tested, mainly in terms of NCs dispersion within the polymeric matrix as it will be discussed below.

We first tested the spray-drying encapsulation of short ligand LHP NCs. Figure 3a shows a SEM image of typical PMMA:PBMMA 50:50 w:w beads obtained by spray-drying encapsulation of CsPbBr3-SL NCs with a heating temperature of 170 °C. The obtained polymeric particles presented a spherical shape. As shown in Figure 3b, the beads size distribution was found to be very wide, the particle size is in the range of roughly 40 nm -2 µm, with an average diameter of ~ 430 nm, calculated from representative samples with a minimum of 500 beads. Most of the obtained polymeric beads were smaller than 1 µm since 90 % of the beads had a diameter lower than 800 nm. It is well known that the size distribution mainly depends on the atomizer technology, [START_REF] Nandiyanto | Progress in Developing Spray-Drying Methods for the Production of Controlled Morphology Particles: From the Nanometer to Submicrometer Size Ranges[END_REF] in this work we used an impactor nozzle atomizer type which generated droplets from 0.1 to 5 µm in diameter. This broad size distribution can be due to random formation of larger droplets, or to droplet fusion before the drying step. [START_REF] Boel | Unraveling Particle Formation: From Single Droplet Drying to Spray Drying and Electrospraying[END_REF] Such high polydispersity and micrometric size objects can be a problem for further use in applications, such as device integration. Different subsequent sorting techniques have been studied, such as cyclone [START_REF] Bögelein | Cyclone Selection Influences Protein Damage during Drying in a Mini Spray-Dryer[END_REF] or cascade impactor, [START_REF] Beck-Broichsitter | Direct Fractionation of Spray-Dried Polymeric Microparticles by Inertial Impaction[END_REF] and could be used in the future to avoid the presence of large beads and to improve the size dispersity.

Figure 3c shows typical images under ambient light and UV excitation of the polymeric powder obtained by spray-drying. The tubular furnace temperature was one of the key parameters of the spray-drying encapsulation process. For a tubular furnace temperature at 130 °C or lower, no powder was collected but instead, a uniform film of polymer was formed on the filter. The solvent evaporation was certainly not complete (Teb(toluene) = 110 °C) and led to an agglomeration of half-liquid half-solid polymers on the filter, which then dried slowly on the membrane to form a uniform film. Even if the tubular temperature was set to 130 °C, the temperature perceived by the droplets within the glass tube is approximately 50°C lower than the target temperature. On the opposite side, for a tubular furnace temperature at 290 °C or higher, a uniform film of polymer was also formed onto the filter but not for the same reason. In this case the formation of the polymeric films was due to beads coalescence. Indeed, the acrylate-based polymers we used in this study have low glass-transition temperatures (Tg,PMMA = 105 °C; Tg,PBMMA = 52 °C). When exposed to high temperatures, these thermoplastic polymers tend to become more viscous and lose their initial shapes. Figure 3d also shows the influence of the tubular furnace temperature on the final PLQY of composite beads containing CsPbBr3-SL NCs. The final powder PLQY was 35 ± 1 % for a process temperature of 170 °C and dropped to 30 ± 1 % at 210 °C and 21 ± 1 % at 250 °C. This trend line is in good agreement with the poor stability of LHPs against thermal stresses, 19 moreover, the PLQY drop might have been caused by ligand desorption during the spray- drying process. PLQY variations compared to bare NCs are discussed below. Similar results on the morphology, size distribution and temperature dependency on PLQY were obtained for CsPbBr3-LL NCs spray-drying encapsulation (Figure S4 andS5). The size distribution was very similar, showing that it is mostly polymer and process dependent. The PLQY of the spray-dried NCs with long ligands also decreased with process temperature increasing, however the loss was smaller compare to short ligands, probably because long ligands can desorb less easily. [START_REF] Akkerman | Strongly Emissive Perovskite Nanocrystal Inks for High-Voltage Solar Cells[END_REF] The NCs dispersion within the beads was further investigated by STEM analysis. HAADF STEM images clearly indicated that CsPbBr3-LL NCs (Figure 4a) after spray-drying were located on the polymeric beads surface and were not encapsulated. To disperse the NCs within the matrix was the most complicated part of this work, indeed we did not succeed in properly encapsulating CsPbBr3-LL NCs with any tested polymers as NCs were always found on the beads surface. We hypothesized that the interaction between acrylate polymeric chains and long ligands of CsPbBr3-LL NCs (oleic acid and oleylamine) were not strong enough to prevent separation between the solidifying polymeric phase and the NCs during the solvent evaporation. The polarity difference between long alkyl nonpolar surface ligands of CsPbBr3-LL and more polar acrylate polymers may explain their poor affinity.

For spray-dried CsPbBr3-SL NCs, HAADF STEM images revealed that NCs were inside the polymeric beads (Figure 4b), which explicitly demonstrated the CsPbBr3-SL NCs encapsulation with the spray-drying process. We believe that in solution the affinity between CsPbBr3-SL NCs and PMMA:PBMMA is increased due to better interaction between ligands and polymeric chains, which consequently prevents any phase separation during the solvent evaporation and polymer solidification. In this case, NCs surface ligands and polymeric matrix had similarities in their chemical nature: propionic acid and butylamine for the NC surfaces; grafted butyl groups for the acrylate polymers. Raino et al. suggested in 2019 to improve the interaction between polymers and ligands by using grafted polymers with specific alkyl chains to match the surface chemistry of CsPbBr3 NCs, [START_REF] Rainò | Underestimated Effect of a Polymer Matrix on the Light Emission of Single CsPbBr3 Nanocrystals[END_REF] which is in line with our observations in terms of NCs-polymers affinity.

To highlight the influence of the nano-encapsulation on the CsPbBr3 NCs properties, PL, PLQY and XRD analyses were performed on spray-dried NCs with long and short ligands and were compared to corresponding bare CsPbBr3 NCs in solution or in film. NC solutions were dispersed in toluene and NC films were made by drop casting NC solutions on a glass substrate under ambient conditions and allowed to completely dry before analysis. PL peaks of NC films with bare CsPbBr3-LL and CsPbBr3-SL NCs were respectively red-shifted by 9 nm and 10 nm compared to the PL peaks in solution (Figure 5c). An increase in FWHM of 6 nm and 8 nm is also observed, respectively. PL redshift and FWHM increase may be attributed to NCs aggregations and bulk-like contribution. [START_REF] Baranov | Investigation into the Photoluminescence Red Shift in Cesium Lead Bromide Nanocrystal Superlattices[END_REF] These observations indicated a partial degradation of the NCs PL properties in solid-state after deposition, which is one of the numerous known stability issues for such materials. [START_REF] Shamsi | Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties[END_REF] The same NCs at solid state but after the spray-drying process exhibited a Concerning PLQY analyses (Figure 5b), when comparing NCs in solution and films of bare NCs, PLQY dropped from 72 ± 2 % to 42 ± 1 % for CsPbBr3-LL NCs, and PLQY dropped even more drastically from 62 ± 2 % to 8 ± 1 % for CsPbBr3-SL NC. The loss of PLQY for LHPs NCs in solid-state is not totally understood but it was demonstrated on bulk LHPs that grain boundaries induced more non-radiative exciton recombination, limiting bulk LHP PLQY. [START_REF] De Quilettes | Impact of Microstructure on Local Carrier Lifetime in Perovskite Solar Cells[END_REF] Thus, the important loss of PLQY for bare CsPbBr3-SL NCs film may be directly linked to the high quantity of grain boundaries induced by the use of short ligands which did not prevent NCs aggregation during solvent evaporation. [START_REF] Akkerman | Strongly Emissive Perovskite Nanocrystal Inks for High-Voltage Solar Cells[END_REF] This hypothesis is greatly supported by the STEM analyses (Figure 1b). Now, when comparing NCs in solution and after spray-drying, PLQY dropped from 72 ± 2 % to 47 ± 1 % for CsPbBr3-LL NCs, and PLQY dropped from 62 ± 2 % to 35 ± 1 % for CsPbBr3-SL NCs. The difference of PLQY conservation between NCs films and spray-dried nanocomposites was weak for CsPbBr3-LL NCs, but for CsPbBr3-SL NCs, the conservation of the initial solution PLQY (62 ± 2 %) is significantly improved after spray-drying encapsulation (35 ± 1 %) compare to NCs film (8 ± 1 %). These observations indicated a reduced number of aggregated NCs for the encapsulated CsPbBr3-SL NCs, in good agreement with PL analyses and STEM images. In general, the loss of PLQY during the spray-drying process may also have been caused by NCs surface ligands lost, which are known to have a very labile nature. Furthermore, the better PLQY conservation for spraydried CsPbBr3-SL NCs compare to bare NCs films strongly supported the benefit of the encapsulation.

Both spray-dried CsPbBr3-LL and CsPbBr3-SL NCs XRD patterns exhibited the expected orthorhombic crystalline structure of CsPbBr3 perovskite. [START_REF] Cottingham | On the Crystal Structure of Colloidally Prepared CsPbBr3 Quantum Dots[END_REF][START_REF] Bertolotti | Coherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite Nanocrystals[END_REF] No additional phase formation due to thermal degradation is observed, which is usually a limiting aspect for LHPs. [START_REF] Dutta | Annealing CsPbX3 (X = Cl and Br) Perovskite Nanocrystals at High Reaction Temperatures: Phase Change and Its Prevention[END_REF] In other words, the encapsulation by spray-drying did not modify the structural properties of CsPbBr3 NCs.

The spray-drying encapsulation in these specific conditions, not only preserved the initial morphological and structural properties of CsPbBr3-SL NCs, but also improved the stability of their optical properties (PL, PLQY) compared to bare NCs in solid-state, which is a crucial problem for many applications. Despite these encouraging results, the final PLQY of 35 % of the CsPbBr3-SL NCs / polymers nano-composite beads is relatively low compare to previous reported works on green emitting LHPs NCs / polymer composite films with good stability. [START_REF] Xin | Highly Stable and Luminescent Perovskite-Polymer Composites from a Convenient and Universal Strategy[END_REF][START_REF] Tong | Direct Hot-Injection Synthesis of Lead Halide Perovskite Nanocubes in Acrylic Monomers for Ultrastable and Bright Nanocrystal-Polymer Composite Films[END_REF] To enhance the NC emission properties, many surface treatments have been explored in the literature reaching higher PLQY and stability, 20 , 21 most of these studies have been conducted on CsPbBr3-LL NCs. We believe that a similar postsynthesis surface passivation on CsPbBr3-SL with appropriate short surface stabilizer (for example zinc bromide or tetrabutylammonium bromide) to keep the NCs inside the beads, would enhance the PLQY of bare NCs. In that way, the nanocomposites beads PLQY should directly benefit from the improvement of the NCs properties, with a better final PLQY. This aspect is under current investigation in our laboratories.

To evaluate the benefit of the spray-drying encapsulation on the CsPbBr3 NCs photo-stability, we followed the evolution of their PL emission under a continuous blue excitation in a LED down-converter device. Figure 6a shows the setup used for photo-stability measurements in ambient conditions. The NCs were excited by a blue LED (λ = 455 nm) with a surface power density of 0.1 W/cm 2 , similar to industrial test conditions for backlighting materials in LCD displays. The bare NCs or spraydried NCs were deposited on the blue-LED with an on-chip configuration, i.e. by drop-casting the NCs solutions directly on the chip (inset in Figure 6a). The emission stability of CsPbBr3 NCs was evaluated by tracing the evolution of the integrated green PL signal.

For bare CsPbBr3-LL NCs (black dots on Figure 6b), the green emission decreased rapidly and continuously when exposed to the blue excitation, indeed the normalized integrated PL dropped to 0.1 after only 13 h and to almost 0 after 50 hours. Such decrease in PL is generally attributed to a poor resistance against photobleaching and is in line with similar reported observations. [START_REF] Meyns | Polymer-Enhanced Stability of Inorganic Perovskite Nanocrystals and Their Application in Color Conversion LEDs[END_REF][START_REF] Huang | Morphology Evolution and Degradation of CsPbBr3 Nanocrystals under Blue Light-Emitting Diode Illumination[END_REF] The same degradation behavior was recorded for spray-dried CsPbBr3-LL NCs (green dots on Figure 6b), even if a small normalized PL of 0.1 is retained after 30 h. The composite beads behaved like bare NCs because CsPbBr3-LL NCs were not encapsulated in polymeric beads.

In the same way, green emission of bare CsPbBr3-SL NCs decreased rapidly and continuously (black dots on Figure 6c), the normalized integrated PL intensity dropped to 0.1 after 55 hours. However, the green emission signal of the spray-dried CsPbBr3-SL NCs was far more intense over time than the bare NCs (green dots on Figure 6c). Specifically, the normalized PL decreased down to 0.25 in the first few hours, but then slowly recovered and stabilized to an average value of 0.52 ± 0.04 from 50 to 200 hours. This better resistance to photobleaching demonstrated that the polymeric beads acted as a barrier against external environments. Likely the hydrophobic matrix limited the diffusion of ambient oxygen and moisture into the bead and slow down the photobleaching of CsPbBr3 NCs. These results highlighted the benefits of the spray-drying encapsulation process on CsPbBr3 NCs, indeed when the CsPbBr3-SL NCs were truly encapsulated we measured a photo-stability improvement.

As mentioned, the green emission of the spray-dried CsPbBr3-SL NCs exhibited a specific behavior during the first hours of the experiment, the PL first decreased, then slowly increased, and finally stabilized for several hours (Figure 6d or in logarithmic scale Figure S6). Because the blue excitation power density was constant (minor variations compare to green variations), these PL variations were directly linked to NCs PLQY variations and thus indicated changes in the ratio between radiative and non-radiative recombination, especially for the first PL quenching and the following PL brightening. We note that for bare CsPbBr3 NCs, only photobleaching due to photo-degradation was observed, thus PL quenching and brightening were probably induced by the spray-drying encapsulation. Previous studies on LHP materials have observed similar PL behavior. [START_REF] Galisteo-López | Environmental Effects on the Photophysics of Organic-Inorganic Halide Perovskites[END_REF][START_REF] Motti | Photoinduced Emissive Trap States in Lead Halide Perovskite Semiconductors[END_REF][START_REF] Lorenzon | Role of Nonradiative Defects and Environmental Oxygen on Exciton Recombination Processes in CsPbBr 3 Perovskite Nanocrystals[END_REF] Galisteo-Lopez et al., [START_REF] Galisteo-López | Environmental Effects on the Photophysics of Organic-Inorganic Halide Perovskites[END_REF] observed strong PL photoactivation under continuous similar blue light excitation on hybrid organic-inorganic LHP bulk film. However, they did not observe early PL quenching, only a final photobleaching mostly due to moisture degradation. In the same way, Lorenzon et al. [START_REF] Lorenzon | Role of Nonradiative Defects and Environmental Oxygen on Exciton Recombination Processes in CsPbBr 3 Perovskite Nanocrystals[END_REF] studied the PL behavior of bare CsPbBr3 NCs under different environmental conditions, they pointed out that PL quenching occurred with the presence of nonradiative defects, especially surface states and dangling bonds, leading to photogenerated carrier trapping. Based on these previous studies on LHP materials and others on Cd-based quantum dots, [START_REF] Carrillo-Carrión | Quantum Dots Luminescence Enhancement Due to Illumination with UV/Vis Light[END_REF][START_REF] Javaux | Thermal Activation of Non-Radiative Auger Recombination in Charged Colloidal Nanocrystals[END_REF][START_REF] Huang | Investigation of Luminescence Enhancement and Decay of QD-LEDs: Interface Reactions between QDs and Atmospheres[END_REF] we assumed that in our case, the first PL quenching event was due to an increasing amount of nonradiative recombination due to carrier trapping. This might have been amplified by the creation of surface defects caused by ligands loss or ligands displacement during the spray-drying process. The following slow brightening indicates an increasing amount of radiative recombination compare to non-radiative, possibly due to trap state passivation. However, to fully understand this competition between PL quenching and brightening, further experiments of photostability under various atmospheres and deeper PL analyses (such as fluorescence lifetime) should be performed to get a better understanding regarding the impact of the polymer matrix on the PL behavior of the encapsulated NCs.

On-chip configurations are known to provide harsh test conditions with high thermal and optical exposure. [START_REF] Xie | Quantum Dots-Converted Light-Emitting Diodes Packaging for Lighting and Display: Status and Perspectives[END_REF] In our case, the thermal stresses were limited because sample local temperature was kept at 20-30 °C during the photo-stability measurements. This was achieved thanks to the relatively low light-power excitation combined with the use of a metal heatsink in our setup. However, the current performances of the composite beads might be even more interesting for less stressful applications such as on-edge or on-surface NCs/LED configurations for backlighting. [START_REF] Coe-Sullivan | Quantum Dots for LED Downconversion in Display Applications[END_REF]

CONCLUSION

We have developed a new method to encapsulate CsPbBr3 NCs within nanometric polymeric beads with a spray-drying process. The combination of acrylate polymers with specific chemical groups (PMMA and PBMMA) matching the short ligands at the surface of the CsPbBr3-SL NCs has allowed us to obtain NCs encapsulated within the beads. Through the spraydrying process, we managed to retain the optical and structural properties of the starting CsPbBr3-SL NCs. The nano-composite CsPbBr3-SL NCs / polymer beads exhibited a PLQY of 35 % and an improved photo-stability at solid-state regarding to the bare CsPbBr3-SL NCs. Indeed, we measured a stable NCs emission under in-use conditions with a LED down-converter, making these spray-dried NCs promising candidates for lightconverting materials. We believe that the optical properties and the photo-stability of CsPbBr3 NCs encapsulated by spraydrying process could be rapidly improved in the future by determining the right NCs surface passivation in the plethora of existing literature. Furthermore, efforts need to be done to reduce the polydispersity of the polymeric beads, and the use of different atomization or size-sorting techniques should help to achieve this objective. The synthesized nano-composite beads in this study could be used directly as final materials, or further incorporated in other types of matrix, or even functionalized. Thus, they may be used for many fields of application in the future, in particular for display applications, biological markers and security encoding.

In a more general context, there is room to explore the spray-drying nano-encapsulation of different types of nanocrystals (fluorescent, plasmonic, magnetic, etc.) in polymeric beads. The spray-drying process should offer a way to synthesize such nano-composite particles with a versatile, inexpensive, and scalable method, thus paving the way for industrialization.

METHODS

Materials.

Lead bromide (PbBr2, 98%), cesium carbonate (Cs2CO3, 99%), oleic acid (OA, 90%), poly(methyl methacrylate) (PMMA, Mw = 120 000 g.mol -1 ), poly(butyl methacrylate-co-methyl methacrylate) (P(BM)MA, Mw = 150 000 g.mol -1 ) and n-heptane (HEP, 99 %) were purchased from Sigma-Aldrich. Toluene (99.8 %), n-hexane (HEX, 95%) were purchased from Carlo Erba. 1-octadecene (ODE, 90 %) and oleylamine (OAm, 90 %) were purchased from Acros. Propionic acid (PrAc, 99.0%) was purchased from TCI. nbutylamine (BuAm, 98%) was purchased from Alfa Aesar. Propanol-2 (IPrOH, 98%) was purchased from VWR.

Synthesis of CsPbBr3-LL NCs. The synthesis of CsPbBr3-LL NCs was adapted from Protesescu et al. [START_REF] Protesescu | Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut[END_REF] 1.2 g of Cs2CO3 (3.7 mmol), 3.6 mL of OA (18.8 mmol) and 45 mL of ODE were introduced in a 100 mL three-neck round bottom flask and heated at 110°C under vacuum for 1 hour. The mixture was then heated to 130°C under nitrogen until the cesium oleate (Cs-OA) formation was completed. The Cs-OA solution was kept at 120°C to avoid solidification. In another 100 mL three-neck round bottom flask, 0.330 g of PbBr2 (0.9 mmol) and 30 mL of ODE were dried under vacuum for 1 hour at 120°C. Then, 3 mL of OA and 3 mL of OAm were added at 120°C under vacuum, the solution was heated for 30 additional minutes. After complete solubilization of PbBr2, the mixture was heated at 180°C under nitrogen with a vigorous stirring. Once the desired temperature was reached, 4.8 mL of Cs-OA (0.8 mmol) solution at 120°C was quickly injected. After 15 s the reaction was rapidly quenched by removing the heating mantle and cooling the flask with an ice water bath. For the purification step, the crude solution was centrifuged at a speed of 9000 rpm for 10 min. The supernatant was then discarded, and the precipitate was dispersed in 6 mL of toluene. The solution was centrifuged once more at a speed of 2000 rpm for 4 min and the supernatant was kept while the precipitate was discarded to remove the non-stable nanocrystals. The obtained CsPbBr3-LL NCs solution was stored under ambient conditions.

Synthesis of CsPbBr3-SL NCs. The protocol synthesis of CsPbBr3-SL NCs was adapted from Akkerman et al. [START_REF] Akkerman | Strongly Emissive Perovskite Nanocrystal Inks for High-Voltage Solar Cells[END_REF] A precursor solution of cesium propionate (Cs-PrA) at 2 M was prepared by dissolving 326 mg of Cs2CO3 in 1 mL of propionic acid at room temperature. Another precursor solution of PbBr2 at 0.25 M was prepared by dissolving 184 mg of PbBr2 in 2 mL mixture of PrAc:IPrOH:BuAm with a 1:1:1 volume ratio. Afterward, 6 mL of hexane, 3 mL of IPrOH and 27 µL of Cs-PrA were added in a 25 mL round bottom flask. The mixture was stirred vigorously under ambient conditions (temperature and atmosphere) and 600 μL of PbBr2 solution was quickly injected. The solution immediately turned to green due to the formation CsPbBr3-SL NCs. The crude solution was centrifuged at 1000 rpm for 2 min, then the supernatant was discarded and the NCs were dispersed in 6 mL of toluene. The obtained CsPbBr3-SL NCs solution was stored under ambient conditions.

Spray-Drying Encapsulation. Typically, 900 µL of CsPbBr3-LL or CsPbBr3-SL NCs of as prepared solutions were mixed with 6 mL of an acrylate polymer solution (4 wt% of PMMA:P(BM)MA 50:50 dissolved in toluene) in a specific vial. We estimated the NCs weight concentration to be around 0.2 wt%. The solution was stirred for 1 hour to ensure a good NCs dispersion in the polymer solution. The temperature of the tubular furnace was set at a temperature between 170 and 290 °C and the nitrogen pressure of the atomizer was set at 1.5 bar. Note that the perceived temperature inside the glass tube is around 50 °C lower than the tubular furnace temperature. The NCs / polymer solution was then plugged to the atomizer, the vacuum pump was turned ON and the nitrogen valve of the atomizer was immediately opened to initiate the atomization of the initial solution into a mist of droplets. Consequently, the mist was allowed to pass through the tubular furnace for solvent evaporation. During the process, the NCs / polymer solution continued to be atomized while the spray dried NCs were collected onto the hydrophilic polytetrafluoroethylene filter (0.22 µm) placed beforehand at the outlet of the furnace. Once the solution was totally atomized (~ 5 min), the nitrogen valve, tubular furnace and vacuum pump were turned off. The dried powder of NCs / polymers composite collected on the filter was transferred and stored in a closed vial under ambient condition.

Preparation of LED Down-Converters. The "on-chip" configuration was used to evaluate the performance of CsPbBr3 NCs in a light-emitting diode (LED) down-converter, with an OSRAM "Deep-blue LED W5SM Golden Dragon" as the blue excitation source. The powder of spray dried NCs was dispersed and sonicated in heptane. 2 µL of the suspension was then deposited directly on the blue LED chip by drop-casting to form a uniform film of spray-dried CsPbBr3 NCs after solvent evaporation. For bare CsPbBr3 NCs, 2 µL of the solution was directly deposited on-chip.

Photoluminescence Quantum Yield Measurement. The PL QY of the spray-dried NCs were measured with an integrating sphere spectrometer (Quantarus-QYPlus from Hamamatsu) and with thin sample to minimize diffusion and reabsorption effects. In order to be as close as possible to real application conditions, we used the same amount of powder as for the preparation of LED down-converters.

Photo-Stability. Photo-stability measurement were carried out under ambient conditions. The commercial blue LED had an excitation wavelength of 455 nm and was used to optically pump the CsPbBr3 NCs on-chip. The LED was powered with a DC current supply (LakeShore 101) at 1 mA to generate a surface power density of 0.1 W/cm2. Indeed, for this working current we measured a light-power of 1.1 mW, divided by the 1 mm 2 LED-chip surface we obtained a light power density of about 0.1 W/cm 2 .The LED was mounted with thermal paste on a printed circuit board attached to a cooler. The emitted signal from the on-chip NCs was collected by an optical fiber and detected with a spectrometer (UV-VIS OCEAN OPTICS STS) to obtain the emission spectrum of the LED down-converter. The emission stability of CsPbBr3 NCs was evaluated by integrating the green PL signal over time.

Instrumentation. TEM/STEM observations were made on a Titan Themis 200 microscope (FEI/ Thermo Fischer Scientific) equipped with a geometric aberration corrector on the probe. The observations were made at 200 kV with a probe current of about 50 pA and a half-angle of convergence of 17 mrad. HAADF-STEM images were acquired with a camera length of 110 mm (inner/outer collection angles were respectively 69 and 200 mrad). Scanning electron microscopy (SEM) images were obtained with a JEOL JSM-7800F Prime for morphological characterization of the polymeric beads. Xray powder diffraction (XRD) patterns were recorded with an Empyrean diffractometer from Malvern-Panalytical equipped with a monochromatized Cu Kα radiation (λ = 1.540598 Å) and a PIXcel detector. The photoluminescence quantum yield (PLQY) of NCs was determined (with 5% of error bar) by using the Quantaurus-QYPlus UV-near-infrared absolute photoluminescence quantum yield spectrometer from Hamamatsu, with λexcitation = 460 nm. UV-visible absorption spectra were recorded on an Agilent Technologies Cary 60 UV-visible single-beam spectrometer. For NC solution, photoluminescence (PL) spectra were measured on a JASCO spectrofluorometer FP 8500, with λexcitation = 350 nm. For film and powder, PL spectra were recorded with the Hamamatsu PLQY spectrometer.

ASSOCIATED CONTENT

Supporting Information. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org High resolution STEM, NC suspension pictures, SEM morphology analyses, photostability data.

Figure 1 .

 1 Figure 1. HAADF scanning transmission electron microscopy images of (a) CsPbBr3-LL NCs and (b) CsPbBr3-SL NCs. (c) Absorption (black line) and emission spectra (green line) of CsPbBr3-LL NCs (top) and CsPbBr3-SL NCs (bottom) in toluene solutions.

Figure 2 .

 2 Figure 2. Schematic illustration of the spray-drying process for the nano-encapsulation of CsPbBr3 NCs in polymeric beads.

Figure 3 .

 3 Figure 3. PMMA:PBMMA 50:50 w:w beads after 170°C spray-drying encapsulation of CsPbBr3-SL NCs: (a) scanning electron microscopy image, (b) size distribution, (c) a picture of powder under ambient light (left) and 405 nm UV excitation (right), and (d) PLQY depending on the tubular furnace temperature, red cross indicates that no beads were obtained at this temperature.

Figure 4 .

 4 Figure 4. HAADF STEM images of (a) CsPbBr3-LL NCs and (b) CsPbBr3-SL NCs both 170 °C spray-dried with PMMA/P(BM)MA 50/50 w/w.

Figure 5 .

 5 Figure 5. (a) Emission spectra and (b) PLQY of CsPbBr3-LL and CsPbBr3-SL NCs: in solution (green), in films obtained by drop casting of bare NCs (red) and after spray-drying process at 170 °C (blue). (c) XRD patterns of spray-dried CsPbBr3-LL NCs (brown) and CsPbBr3-SL NCs (purple) with XRD pattern of orthorhombic CsPbBr3 ICSD 98-009-7851 (black).

Figure 6 .

 6 Figure 6. Photostability over time of bare NCs and spray-dried NCs under continuous illumination (0.1 W/cm 2 ; blue LED 455 nm) in an onchip configuration. (a) Images of the setup (inset: NCs on-chip). Normalized integrated PL evolution over time of (b) CsPbBr3-LL NCs and (c) CsPbBr3-SL NCs with bare NCs (black points) and spray-dried NCs (greens points). (d) Evolution of the corresponding emission spectrum of the LED down-converter with spray-dried CsPbBr3-SL NCs.

ACKNOWLEDGMENT

We acknowledge Sophie Nowak for XRD analysis, Delphine Martin for assistance on Sketchup software, Edgar Cao and Sebastien Dreyfuss for proofreading of the manuscript.

ABBREVIATIONS

FWHM, full width at half maximum; LED, light-emitting diode; LHP, lead halide perovskite; LL, long ligand; NC, nanocrystal; PL, photoluminescence; PLQY, photoluminescence quantum yield; PMMA, poly(methyl methacrylate); P(BM)MA, poly(butyl methacrylate-co-methyl methacrylate); SEM, scanning electron microscope; SL, short ligands; STEM, scanning transmission electron microscope; XRD, X-ray diffraction

Funding Sources

This work was supported by the French RENATECH network, the Project TEMPOS (10-EQPX-0050) of the French National Research Agency (ANR) and Nexdot.

AUTHOR INFORMATION Corresponding Author

* Félix Boussoufi: fe.boussoufi@gmail.com

Author Contributions

FB designed and conducted experiments, analyzed data, and wrote the paper. MP analyzed data and finalized the paper. MD and AK designed the spray-drying process. GP conducted microscopic observations. GP and BD supervised the project and acquired funding. All authors have given approval to the final version of the manuscript.

Notes

The authors declare no competing financial interest.


Véronique Guilloux
email: veronique.guilloux@univ-paris12.fr

Claire Gauzente
email: claire.gauzente@univ-angers.fr

Does psychological profile have something to do with satisfaction? A French retailing franchisees study

Keywords: franchisees, psychological profile, personality, satisfaction

The main purpose of this study is to analyse the relationship between franchisee's personality and franchisee's satisfaction. A sample of 400 French franchisees concerning different sectors is analysed in detail. In the first part of the article, the methodology is presented. Then, theoretical framework concerning satisfaction and personality is developed. Different hypotheses are justified crossing the MSQ scale and the big four model. Conscientiousness seems to be the most predictive factor for satisfaction and results show that the other Big-Five traits are specific in several sectors.

Introduction

Franchising is a major component of the French distribution system. French franchise system holds the leader position in Europe in terms of sales (http://www.franchisefff.com/).

Numerous magazines explain to a wide audience, franchise opportunities, but the academic community seems to be lacking of theoretical frames. Many handbooks show the important role of the franchisee concerning the success of a franchise network, but paradoxically few empirical researches have tried to understand the psychological antecedents (personality) of satisfaction (except [START_REF] Morrison | How franchise job satisfaction and personality affects performance, organizational commitment, franchisor relations, and intention to remain[END_REF][START_REF] Schell | Personality and attitudinal predictors of commitment for franchisees[END_REF][START_REF] Tuunanen | Franchisees' satisfaction: preliminary findings from national study[END_REF]. Study of the scientific literature, in addition to examining our own exploratory interviews, has persuaded us to retain the variable 'psychological profile of franchisees' to explain satisfaction. The main purpose of this study is to analyse the relationship between franchisee's personality and franchisee's satisfaction. A sample of 400 French franchisees concerning different sectors is analysed in detail. In the first part of the article the methodology is presented. Then theoretical framework concerning satisfaction and personality is developed. Different hypotheses are justified crossing the MSQ scale and the big four model. Results of the empirical study are then detailed. Directions for future research are outlined.

Methodology: sample and sectors

This research was funded by the French Franchise Federation. Several stages must be identified in our research. The diagram below synthesises the various phases involved in collecting data.

Figure 1 The collection of data A guide was developed to interviewing technique, in order to establish qualitatively franchisees' motivations, their reasons for satisfaction and their selection processes (approached through accounts of their own experience). Twenty one in-depth interviews were carried out with franchisees. Industrial sectors were as follows: property, fast food, optics, food distribution, automobiles, clothing textiles, hairdressing, wines and spirits, soft furnishings and shoes.

By the end of this first stage, two questionnaires were framed:

• questionnaire for franchisors: questions dealing with their perception of the reasons for selecting applicants for franchising

• questionnaire for franchisees: identity, psychological profile, type of relationship with franchisors and satisfaction. In this paper, we focus on the franchisee population.

The aim was to acquire a representative sample of franchisees. Defining the research quotas was achieved in four phases:

• Calculating with the help of the Franchise Yearbook the percentages of franchises in each sector. • Requesting 240 franchisors to supply a list of their franchisees. A mailing has been done with French Franchise Federation headed notepaper.

• Receiving 40 lists comprising 4,659 franchisees. • Calculating the quotas of franchisees to question, bearing in mind that our aim is to collect 400 valid questionnaires. This number has been chosen in partnership with GFK and the French Franchise Federation. Cuisines Plus/Bains plus 2

Note: 1 The number of franchisees in each sector is calculated by multiplying the total number of the sample by the percentage of franchisees in the sector in question in the base population. For example, in the specialised food trade, the statistics of the base population show that the franchisees of that sector represent 3.98% of all French franchisees. Thus, in our survey we must question 3.98% of 400, that is, 16 franchisees. Total 400

Note: 1 The number of franchisees in each sector is calculated by multiplying the total number of the sample by the percentage of franchisees in the sector in question in the base population. For example, in the specialised food trade, the statistics of the base population show that the franchisees of that sector represent 3.98% of all French franchisees. Thus, in our survey we must question 3.98% of 400, that is, 16 franchisees.

Questioning was carried out on the telephone by GFK 1 . Four hundred valid franchisees' questionnaires were obtained and used in order to test our model for researching the level of satisfaction among franchisees.

Concepts of personality and satisfaction

We now present the variable 'psychological profile' from a conceptual point of view, going on to investigate the connections between franchisees' profiles and satisfaction.

Personality

There are many current theories on personality. We look at the main ones, before explaining which of them we selected as appropriate to our study.

The different approaches

According to Cattell, the history of personality theories can be divided into three periods.

The first was literary, philosophical and intuitive (Hippocrates). In the second, an extensive process of theorisation took place (psycho-analytical theory, Freud, Jung and so on). The third was quantitative and operational, and the notion of distinctive traits came to the fore (Murray, Gordon and others). Writers sought to isolate useful and accurate dimensions to define individuals. No longer is it our aim to discover the unconscious reasons that underlie individual behaviour: it is rather to identify individual differences that are sufficiently stable for us to denominate them as traits of the personality. To establish these differences, we start by making inventories of the personality made up of several hundred questions. The replies enable us to define the individual in relation to personality traits such as aggression, the need for change, dependence, autonomy, exhibitionism and so on. The trait point view assumes that people possess predisposition, called personality traits which refer to patterns in the way individuals behave, feel and think. This approach is based on a nomothetic focus (which studies what the humans have in common and tries to draw general laws) opposed to idiographic process (which favours case studies). Besides, traits approaches to personality emphasises the human's internal working rather than the characteristics of the situation.

The best known quantitative model is a model based on five dimensions, the so-called Big-Five, which are said to compose the main aspects of personality [START_REF] Pervin | Trait theory: the five-factor model; applications and evaluations of trait approaches to personality[END_REF]. The Big-Five are now considered indispensable to researchers in management or psychology who may be working on problems of personality.

Conception

Using Big-Five analysis, there are two types of methods for defining personality: the lexical approach (using simple adjectives) and the classical questionnaire (in the form of sentences).

The material used as a corpus is based on lexical analysis of those terms most commonly used in the natural languages to describe the personalities of individual people. Character traits are revealed in ordinary social interaction and are expressed in everyday language [START_REF] John | The lexical approach to personality: a historical review of trait taxonomic research[END_REF]. The psychologist seeking to paint a panoramic view of personality traits needs only to consult a dictionary. [START_REF] Peabody | Selecting representative trait adjectives[END_REF] and [START_REF] Peabody | Some determinants of factor structures from personality-trait descriptors[END_REF] both show that personalities can be assessed with the help of simple adjectives.

The approach through a classical questionnaire depends on using whole sentences. One can offer the example of [START_REF] Costa | From catalog to classification: Murray's need and the five-factor model[END_REF] who base their questions on the Big-Five.

The scale

We explain which structural model of personality we chose for our research, and more particularly why we opted for the lexical method. We shall present the questionnaire we used.

Choosing the Big-Five model

We stayed with the Big-Five to define franchisees' personalities. The choice was made for several reasons: the model is recognised by the scientific community having been tested in many countries; numerous studies relate the Big-Five to performance [START_REF] Robertson | Understanding management performance[END_REF] and our theme falls within the framework of industrial marketing with a managerial perspective.

Choosing the lexical method

From the various models we have selected the lexical method. Indeed, using the telephone to conduct our questionnaire dictated the need for a brief form of words.

In the study by [START_REF] Borkenau | The Big Five as states: how useful is the five-factor model to describe intraindividual variations over time?[END_REF]: the number of items is small (30); the adjectives are familiar and easily understood; the list has already been tested in a European context. The following table sets out the various adjectives applying to each of the super-factors. Each dimension is evaluated in the left-hand column, with the help of three positive adjectives and three opposed ones. Each dimension is tied with six items. In our questionnaire, we placed items in alphabetical order, to maintain strict objectivity. We asked people to respond spontaneously to each item via note from 0 to 10 points. The Big-Five approach is based on factor analysis. Several factors analysis has been done to have a good quality of representation. Only nine items have been selected representing the four factors of the Big-Five. The total percentage of the variance accounted for by these four factors is 69,181%.

(factor 1 -26,337%; factor 2 -15,373%, factor 3 -15,309%, factor 4 -12,162%). The Big-Five are represented with conscientiousness; extraversion (-)/introversion (+); neuroticism; intellect.

Satisfaction among franchisees

Before setting out the approach we favoured in the context of this research, we shall describe the approaches that were used in previous studies where the problems of franchising were specifically targeted.

Approaches used in the specialised literature

Channel satisfaction and job satisfaction will be reviewed.

Channel satisfaction

In studies on the satisfaction of franchisees, channel satisfaction is generally conceptualised as a response of individual channel members towards salient aspects of the channel organisation. For [START_REF] Schul | Members' satisfaction[END_REF], a franchisee's overall satisfaction with the channel arrangement is based on his specific feelings regarding the quality of: franchise administration, service support, rewards and franchise fee policies. For [START_REF] Lewis | A model of channel member performance, dependence and satisfaction[END_REF], satisfaction is tied with three concepts: satisfaction with multiple dimensions of role performance, overall satisfaction with role performance and satisfaction with business decision. Role performance was evaluated by using 117 items distributed among eight business functions (product, physical distribution/customer service, operations, promotion, real estate and construction, pricing, personnel, training).

Overall satisfaction was measured by a continuum from 'poor' to 'excellent'. Finally, a single item measure was used to assess how satisfied franchisees were with their initial decision to join the franchise system. [START_REF] Hing | Franchisee satisfaction: contributors and consequences[END_REF][START_REF] Hing | Developing a model of franchisee buying behaviour based on the Australian restaurant industry: directions for future research[END_REF]) approach proposes a model for the determining factors of franchisees' satisfaction. Inspired by models of consumers' behaviour, she measures satisfaction against a series of items characterising the activity of the franchise.

Job satisfaction

The global or faceted approaches can be utilised to measure the satisfaction of franchisees at work. The global approach is used in [START_REF] Brayfield | An index of job satisfaction[END_REF]. The item was 'I am really very satisfied with my work' or 'I take a real pleasure in my work'.

In the faceted approaches, the identification of the multi-facets of job has done a lot of publications [START_REF] Heneman | Attributions and exchanges: the effects of interpersonal factors on the diagnosis of employee performance[END_REF]. The scale that is utilised to measure job satisfaction is for example: the Minnesota satisfaction questionnaire (MSQ) [START_REF] Weiss | Manual for the Minnesota satisfaction questionnaire[END_REF].

The scale

The approach that we have preferred in the present study takes several considerations into account. Firstly, in conformity with earlier theoretical developments, job satisfaction is measured through facets. Speaking generally, the MSQ is one of the most widely used studies and was also used in Morrison's research. Moreover, in the French context, a reliable translation of this scale is available. Secondly, nevertheless, it seemed to us after our exploratory interviews that the items in the version (20 items) were not all applicable in the context of franchising. Accordingly, our team selected and adapted items to suit the aims and the context of our research. The resulting scale for the franchisee's job satisfaction comprises nine items. Moreover, as regards remuneration, we thought it important to distinguish several levels: remuneration as payment for the work done, which is an integral part of the MSQ and thus of job satisfaction; remuneration arising from the efficient running of the franchised outlet, with two distinctions: the volume of turnover and the profitability of the franchised outlet.

It also became clear in the course of our exploratory interviews that some dimensions could be linked, such as satisfaction as to the location of the franchised outlet.

In total, the items we have used are as follows with a note from 0 to 10: During the Salon de la Franchise, a pre-test for this scale was carried out with franchisees.

The calculation of the alpha for the reliability of the scale for franchisees' job satisfaction as applied to the pre-test sample gives a good result. This was confirmed against the definitive national sample. We may note that transposing the MSQ to the context of franchising retains the reliability qualities of the measuring scale. Over the definitive survey, the good internal consistence of the scale is amply confirmed; this enables us, firstly, to use the sum of the nine items to evaluate job satisfaction. This procedure is also legitimised by a factorial analysis that extracts a single factor according to the criterion of proper value (% of variance explained: ~52%, KMO: .885).

Satisfaction and psychological profile

Support for the relationship between Big-Five personality traits and job performance or job behaviour predictors can be attributed to several meta-analyses. Two of the earliest meta-analyses are those of [START_REF] Barrick | The Big Five personality dimensions and job performance: a meta analysis[END_REF] and [START_REF] Tett | Personality measures as predictors of job performance: a meta-analytic review[END_REF]. Many different academic authors have reported a relationship between the Big-Five Model and job performance/success or career satisfaction. Intellect: sometimes called openness to experience, comprises the capacity for knowledge and analytical thinking. DeNeve and Cooper (1998) noted that 'openness to experience is a 'double-edged sword' that predisposes individuals to feel both the good and the bad more deeply ' (p.199), rendering its directional influence on job satisfaction unclear.

H1 Intellect is negatively connected to satisfaction Conscientiousness: [START_REF] Organ | Personality, satisfaction, and organizational citizenship behavior[END_REF], [START_REF] Barrick | The Big Five personality dimensions and job performance: a meta analysis[END_REF] and [START_REF] Judge | Five-factor model of personality and job satisfaction: a meta-analysis[END_REF] showed that Conscientiousness should be related to work satisfaction because it means a job involvement tendency which leads to a greater likelihood of obtaining satisfying work rewards.

H2 Conscientiousness is positively connected to satisfaction

Extraversion: extraverts are predisposed to experience positive emotions [START_REF] Costa | Four ways five factors are not basic: reply[END_REF] and positive emotionality likely generalises to job satisfaction [START_REF] Connolly | The role of affectivity in job satisfaction: a meta-analysis[END_REF][START_REF] White | Big five personality variables and relationship constructs[END_REF]. Extraverts have more friends than introverts and, because of their social facility, are likely to find interpersonal interactions more rewarding [START_REF] Watson | On traits and temperament: general and specific factors of emotional experience and their relation to the five-factor model[END_REF].

H3 Extraversion is positively connected to satisfaction

Agreeableness: [START_REF] Mccrae | The NEO personality inventory: using the five factor model in counseling[END_REF] and [START_REF] White | Big five personality variables and relationship constructs[END_REF] argued that Agreeableness should be related to happiness because it leads to greater motivation to achieve interpersonal intimacy and greater levels of well-being. [START_REF] Mount | Five-factor model of personality and performance in jobs involving interpersonal interactions[END_REF] demonstrated that agreeableness is a good predictor in jobs where interpersonal interaction and teamwork are important.

H4 Agreeableness is positively connected to satisfaction

Neuroticism: Because of their essentially negative nature, neurotic individuals experience more negative life events than other individuals [START_REF] Magnus | Extraversion and neuroticism as predictors of objective life events: a longitudinal analysis[END_REF]. They select themselves into situations that foster negative effect [START_REF] Emmons | Choice of situations and congruence models of interactionism[END_REF].

H5 Neuroticism is negatively connected to satisfaction 5 Results of the empirical study

Five hypotheses are proposed: H1 -Intellect is negatively connected to satisfaction; H2 -Conscientiousness is positively connected to satisfaction; H3 -Extraversion is positively connected to satisfaction; H4 -Agreeableness is positively connected to satisfaction and H5 -Neuroticism is negatively connected to satisfaction.

Starting from our index of 400 representative franchisees, we investigated the different research hypotheses relating franchisees' personalities to their level of satisfaction. The results of the MSQ scale are only tied with one psychological profile. One factor of the Big-Five, conscientiousness correlates with satisfaction at work. To validate this result, partial correlations has been done for MSQ variables selecting two control items [In your present franchise, are you satisfied with the annual turnover you have achieved over the past three years? (0 to 10) and in your present franchise, are you satisfied with the profitability you have achieved over the past three years? (0 to 10)].

The results are significant except for the MSQ9 item. It confirms the fact that Conscientiousness is tied with satisfaction and it is consistent with literature.

Conscientiousness embodies characteristics such as responsibility, dependability and reliability, all of which are generally perceived as important characteristics for success in most jobs [START_REF] Barrick | The Big Five personality dimensions and job performance: a meta analysis[END_REF][START_REF] Murphy | Personality variables related to integrity test scores: the role of conscientiousness[END_REF][START_REF] Salgado | The five factor model of personality and job performance in the European community[END_REF]. [START_REF] Cook | An Investigation of the Construct Validity of the Big Five Construct of Emotional Stability in Relation to Job Performance, Job Satisfaction, and Career Satisfaction[END_REF] writes in his dissertation 'Conscientiousness could be called the 'GMA' (General Mental Ability) of personality testing, in that it is a 'universal' predictor, predicting performance for all jobs in all contexts.' Despite the fact that Conscientiousness seems to be the most predictive factor, it is generally agreed that the others also contribute unique information since the Big-Five traits seem to be only minimally correlated. The other four personality dimensions have also been shown to be good predictors of job outcomes in certain contexts and for certain performance criteria [START_REF] Barrick | The Big Five personality dimensions and job performance: a meta analysis[END_REF]. In particular, Extroversion emerges as other strong predictors of many job criteria in a variety of job contexts [START_REF] Murphy | Personality variables related to integrity test scores: the role of conscientiousness[END_REF][START_REF] Barrick | The Big Five personality dimensions and job performance: a meta analysis[END_REF]. For example, [START_REF] Stewart | Personality dimensions and domains of service performance: a field investigation[END_REF] found that, Extroversion was a valid predictor of overall performance for service workers. [START_REF] Salgado | The five factor model of personality and job performance in the European community[END_REF] found Agreeableness to be a valid predictor for professionals, skilled labour and managers.

In order to deeper our research, potential links between different variables (sector and satisfaction; sector and psychological profile) have been analysed.

The table presents the results of one way ANOVA procedure for satisfaction and different sectors. Are there specific sectors where satisfaction at work is higher than elsewhere?

The results show that sectors present differences among the means concerning the MSQ (satisfaction at work). Household equipment has the higher mean, followed by non-specialised food trade.

In our sample, household equipment sector is represented by signs like Catena; Maison de la Literie; Cuisines Plus; non-specialised food trade sectors are associated with Casino, Huit à Huit and Champion. This king of franchise represents large volume distribution and is a speciality of French retail. Besides in this kind of shop, the number of employees is bigger than in the others. Professionalisation, formalisation, work specialisation, structures of these franchise networks and perhaps less competitive environment could explain the results. The table presents the results of one way ANOVA procedure for psychological profile and different sectors. Are there specific sectors where specific Big-Five dimensions are more present than elsewhere?

The results show that sectors present difference among the means concerning introversion and neuroticism. Franchisees in the personal equipment sector are more extroverted and less neurotic. This is the same things for the 'Other non-food specialised business' sector.

The personal equipment sector is represented by shops of clothing Rodier, La Compagnie des Petits, Phildar and Petit Boy. Other non-food specialised business sector is also represented by small shops and require intensive for the franchisees work in the store. Franchisees spend a lot of time in social situations (customer services, empathy, advices, interactions…). Extravert personality is welcome for front office work.

Surprisingly, many franchisees are introverted and more neurotic. This does not mean that they are inevitably unsatisfied. Introversion could be compatible with back office positions (for example book keeping, procurement, stock management) or supra management when they are multi-unit-franchisees. In summary, results of the current quantitative research among 400 franchisees indicate that conscientiousness is relevant to predict job satisfaction. The relations between satisfaction (MSQ) and the other factors of the Big-Five (introversion, neuroticism, intellectual) are not significant. Despite the fact that Conscientiousness seems to be the most predictive factor for satisfaction, results show that the other Big-Five traits are specific in several sectors. The type of franchisees activity is a contextual variable. For example, extraversion characterises the personality of franchisees working in the personal equipment sector. This specific trait does not explain franchisee's satisfaction but is certainly essential to reach customer's satisfaction. Literature shows that Big-Five personality dimensions, not just Conscientiousness, have value as predictors of job performance. If this study proves that franchisees' satisfaction is tied with Conscientiousness, future research concerning the Big-Five and franchisee's different job criteria or job performance (commitment to the organisation, workplace stress, job strain, market oriented organisation, customer orientation, leadership, supervision, motivation in the workplace, interpersonal communication etc…) should be developed in future research.

Table 1

 1 Questioning methodology

	Characteristics	Survey of potential	Survey of franchisors Survey of franchisees
		franchisees
		Preliminary survey of
		franchisees
	Target	Franchisees	Franchisors	Franchisees
		(qualitative method)
	• Means of	Face to face	Face to face	Telephone interviews
	collection	interviews	interviews and	carried out by GFK
		In-depth interviews	questioning by post
	• Overall population	21 interviews were	List of franchisors in	List of 4,659
		conducted in four	the Franchise	franchisees
		different regions of	Yearbook (240)
		France
	• Size of sample	21 franchisees	88 questionnaires	400 questionnaires

Table 2

 2 The overall population

	Number of	Number of	%	%
	franchisors	franchisees	franchisors	franchisees

Table 3

 3 The answers obtained from the franchisors

		Number of	Number of	%	%
		franchisors	franchisees	franchisors	franchisees
	1 Specialised food trade	5	270	12.50%	5.80%
	2 Non-specialised food trade	3	1,491	7.50%	32.00%
	3 Personal equipment	7	358	17.50%	7.68%
	4 Household equipment	3	299	7.50%	6.42%
	5 Other specialised non-food	7	535	17.50%	11.48%
	businesses
	6 Services	11	1,364	27.50%	29.28%
	7 Hotels and restaurants	3	332	7.50%	7.13%
	8 Building	1	10	2.50%	0.21%
	Total	40	4,659 1	100.00%	100.00%
	Note:

1

That is, 18.86% of the base population.

Table 4

 4 The makeup of research quotas

		Number of	Name of franchisors	Number of
		franchisees to be		franchisees
		questioned 1		interviewed
	1 Specialised food	16	Point chaud	1
	trade		Comtesse du Barry	9
			Deneuville	6
	2 Non-specialised food	47	Casino	15
	trade		Huit à Huit	18
			Champion	14
	3 Personal equipment	71	Rodier	14
			La compagnie des petits	23
			Phildar	30
			Petit Boy	2
			Descamps	2
	4 Household equipment	39	Catena	16
			Maison de la Literie	21

Table 4

 4 The makeup of research quotas (continued|)

		Number of	Name of franchisors	Number of
		franchisees to be		franchisees
		questioned 1		interviewed
	5 Other specialised	47	La Trocante	17
	non-food businesses		Bazar Land	10
			Magasin Gamm Vert	11
			Troc De L'île	1
			Distri Club Medical	8
	6 Services	140	Mister Mint	15
			Jack Hiolt Quick Service	19
			L'onglerie	20
			Speedy	11
			L'age D'or Services	12
			Feu Vert	5
			Mod'hair	5
			Unicis	6
			Etape Auto	7
			Century 21	42
	restaurants 7 Hotels and	36	Comfort, Quality Hotels	11
			Café Leffe	17
			Quick	8
	8 Building	0

Table 5

 5 Borkenau and Ostendorf's items

	Speaking for yourself, and completely frankly, are you?:
		Intellect (+/-)
	Witty, quick-minded	(-) Easily beaten, easily lost, out of one's depth
	Well informed, well documented, expert	(-) Unaware, rash
	Cautious	(-) Unimaginative
	Conscientiousness (+/-)
	Hard working	(-) Nonchalant
	Persistent	(-) Imprudent, unthinking
	Serious, responsible	(-) Instable
	Extraversion (+/-)
	Dynamic	(-) Timid
	Sociable	(-) Silent, taciturn
	Full of drive	(-) Reserved
	Agreeableness (+/-)
	Easy to get on with	(-) Selfish
	Obliging	(-) Authoritarian
	Thoughtful, considerate	(-) Obstinate
	Neuroticism (+/-)
	Irritable	(-) Emotionally stable
	Ill-natured	(-) Calm
	Vulnerable	(-) Tough

Table 6

 6 Quality de representation

	Speaking for yourself, and completely frankly	Initial	Extraction
	you are imprudent; unthinking	1,000	,679
	you are…irritable	1,000	,783
	you are reserved	1,000	,722
	you are tough	1,000	,638
	you are serious responsible	1,000	,614
	you are silent, taciturn	1,000	,642
	you are witty, quick-minded	1,000	,891
	you are persistent	1,000	,609
	you are hard working	1,000	,649

Table 7

 7 Factor analysis after rotation (varimax)

		Speaking for yourself, and completely		Factors
		frankly,	1	2	3	4
	Conscientiousness	you are tough	,791
		you are hard working	,753			-,208
		you are persistent	,742			,222
		you are serious responsible	,730			,238
	Extraversion (-)	you are reserved		,842
	Introversion (+)	you are silent taciturn		,771
	Neuroticism	you are...irritable			,866
		you are imprudent; unthinking	-,228		,742
	Intellect	you are witty, quick-minded				,936

Table 8

 8 Items selected for measuring the satisfaction of franchisees

	Wording of the items

HING 13 All things considered, would you recommend the franchise to a friend? Our own measure

Table 9

 9 Reliability study for job satisfaction applied to franchisees

	Items MSQ	Scale without item pre-test	Scale without item
			N = 21	N = 401
		Are you satisfied:
	1	With your working conditions?	.8622	.8634
	2	With the social status that your work	.8680	.8594
		gives you?
	3	With the security of your job?	.8808	.8601
	4	That you can use your personal	.8799	.8618
		qualities?
	5	That you can take decisions on your own	.8721	.8629
		initiative?
	6	With your occupation during the	.8864	.8672
		working day?
	7	That you can put into practice your own	.8756	.8755
		working methods?
	8	With the feeling of achievement that	.8786	.8550
		your work offers you?
	9	With your income in relation to the work	.9255	.8793
		you do?
	Number of items = 9	Alpha = .8939	Alpha = .8782

Table 10

 10 Pearson correlations

			Conscientiousness Introversion Neuroticism Intellectual
	MSQ	Corr Pearson	.399(**)	-.061	.000	.042
		Sig. (bilateral)	.000	.226	.997	.401
	In your present	Corr	.226(**)	.013	-.003	-.045
	franchise, are you
	satisfied with the
	annual turnover you have achieved over	Sig.	.000	.788	.952	.373
	the past three years
	In your present	Corr	.217(**)	.087	.012	-.028
	franchise, are you
	satisfied with the
	profitability you have achieved over the past	Sig.	.000	.082	.808	.577
	three years?
	All things considered,	Corr	.311(**)	-.034	.018	-.038
	do you intend to
	remain in your	Sig.	.000	.495	.723	.446
	present network?
	All things considered,	Corr	.274(**)	-.028	-.020	-.079
	would you
	recommend the	Sig.	.000	.574	.689	.114
	franchise to a friend?

Table 11

 11 Links between MSQ scale and conscientiousness trait

	Conscientiousness

Table 12

 12 ANOVA: MSQ scale and sectors

			Sum of		Mean
			squares	df	square	F	Sign
	MSQ * sector	Between groups	3,166.736	6	527,789	3.530	.002
		Within groups	58,913.828	394	149,527
		Total	62,080.564	400
	In your present franchise, are you satisfied with the annual	Between groups	27.576	6	4,596	.987	.433
	turnover you have achieved over the past three years? * Sector	Within groups Total	1,833.860 1,861.436	394 400	4,654
	In your present franchise, are you satisfied with the	Between groups	28.550	6	4,758	1.066	.382
	profitability you have achieved over the past three years? * Sector	Within groups Total	1,758.074 1,786.623	394 400	4,462

Table 13

 13 Mean for MSQ by sectors

	Sector	MSQ mean	Std. dev
	Specialised food trade	66.7647	14.94795
	Non-specialised food trade	72.3542	10.74361
	Personal equipment	66.8750	13.64328
	Household equipment	74.6667	8.32034
	Other specialised non-food businesses	70.1915	11.49790
	Services	71.0141	13.10026
	Hotels and restaurants	64.6667	10.40330

Table 14

 14 ANOVA big four and sectors

			Sum of squares	df	Mean square	F	Sign
	Conscientiousness	Between groups	7.668	6	1.278	1.283	.264
	* sector	Within groups	392.332 394	.996
		Total	400.000 400
	Introversion *	Between groups	13.695	6	2.282	2.328	.032
	sector	Within groups	386.305 394	.980
		Total	400.000 400
	Neuroticism *	Between groups	23.348	6	3.891	4.071	.001
	sector	Within groups	376.652 394	.956
		Total	400.000 400
	Intellect * sector	Between groups	8.255	6	1.376	1.384	.220
		Within groups	391.745 394	.994
		Total	400.000 400

Table 15

 15 Mean of introversion and neuroticism by sectors

	Sector

Acknowledgements

This research was funded by the French Franchise Federation. The project was initiated and coordinated by Professor Michel Kalika.