Top-down production of cerium doped yttrium aluminum garnet (YAG:Ce) nanocrystals. Influence of grinding process on cerium valence state

Today, nanophosphors are required for various applications, including association with micro-LED. Two routes can be used to achieve nanosized phosphor particles namely bottom-up and top-down. As part of a PhD thesis, we applied the second one to produce cerium-doped yttrium aluminum garnet (YAG:Ce). However, the used grinding process is responsible of a drop of optical properties, which has been correlated with the formation of an amorphous layer at the nanocrystal surface. On the basis of the evolution of UV spectra profile, we postulated partial in-situ cerium (III) oxidation into cerium (IV), which could be concomitant with amorphization. To the best of our knowledge, this doping element valence modification during grinding has been reported for other phosphors, but not for cerium in YAG matrix. Consequently, the goal of the present proposal is to confirm this hypothesis through X-ray absorption spectroscopy to determine Ce4+ /Ce3+ ratio on milled samples.