Phd contract in the field of Chemistry financed for three years by the University of Clermont Auvergne

Synthesis and characterization of nanophosphors suitables for micro-LEDs-based devices

Besides the more and more common use of Light Emitting Diodes (LEDs) in our everyday life, a new type of miniature LEDs (micro-LEDs) has emerged last years. This pioneering technology,developed by a team of CEA LETI, represents an importantstep forward for many applications such as smart lighting devices, augmented reality using smart glassesor even3D flexible, large and transparent screens.The phosphors currently used in solid-state lightingare not suitable for micro-LEDs based devices, especially because of their size. When using micro-LEDs displays, the elementary unit is a pixel made of an InGaN blue LED structured on a micrometric scale (pixel size comprised between 3 and 10 μm). As for White LEDs (WLEDs), blue light emitted by InGaN has to be converted in white, red or green light using color-converting phosphors. A breakthrough technology employing tailorable submicronic, even nanometric, phosphors is thus required.Size reduction of phosphors can be carried out using two strategies: a top-down approach based on a grinding process which generally generates a lot of defects causing a significant decrease in emission properties of the ground phosphors; a bottom-up approach leading to nanophosphors whose optical features are far from competing with those of micrometric phosphors.Only the quantum dots (QDs) based on cadmium currently provide both interesting performances and sizes compatible with the foreseen applications,but their toxicity hampers them to be widely used over the long term. Furthermore, like organic phosphors, QDs are not stable under thermalor photonic stresses which represents a crippling point for their use in micro-LEDs displays. The development of highly performant and stable nanophosphors thus remains a big challenge. It is in this context that this thesis should be consideredsince its main objective will be the elaboration of inorganic efficient and eco-friendly nanophosphors whose featureswill be stable under both photonic and heatstresses.Phosphors will be elaborated through soft-chemistry processes (microwave assisted or not solvothermal way for example) for which different parameters will be optimized (solvent, pH, temperature, duration...). Studies in surface chemistry will also be led to improve the optical properties of the elaborated nanophosphors. The developed matrices will belong to aluminates or vanadates families.