YVO4:Eu luminescent nanoparticles can be used individually as biolabels or assembled in thin films. For those two applications, it is known that there is a strong correlation between their nanostructure and their optical properties. Thus it would be very pleasant to be able to control it. In the first part, the nanoparticle formation has been studied through time-resolved X-Ray scattering experiments (SAXS/WAXS) coupled with photoluminescence. The first step of their formation mechanism consists in precipitating a slightly luminescent amorphous phase which contains all the precursors. Then, the YVO4 phase crystallizes in small grains (~4 nm) which appear directly at their final state. We name it pop-corn nucleation. Finally, those grains aggregate in hierarchical nanoparticles (~40 nm). Through this study, we figured out that the final particle nanostructure is strongly linked to the amorphous phase initial structure. In the future, working on the early precipitate could be an efficient way to control the structure at the nanoscale. In the second part, we focused on luminescent and transparent thin films made by nanoparticle spray deposition. As this process involves a drop drying step, we had to deal with the coffee-ring effect. This last one is known to cause anisotropic nanoparticle deposition. At the end, it gives scattering coatings. Hopefully, we were able to suppress it and thus increase the thin films transparency owing to a shape control on the drop deposits. Those results were applied to different luminescent nanoparticles in order to produce the most luminescent and transparent coatings. At the end, we extended our work on films to upconverting materials.
