Ce ~(3+) -doped Y _(3) Al _(5) O _(12) (YAG:Ce) nanocrystals were synthesized by a unique solvothermal method, under sub-critical conditions. A home-made autoclave was used, operating in a larger pressure and temperature range than that with conventional commercial equipment and allowing direct in situ photoluminescence (PL) and X-ray absorption characterizations. The study of various synthesis conditions (pressure, temperature, precursor concentration, reaction time) allowed the best reaction conditions to be pinpointed to control YAG:Ce nanocrystal size, as well as crystal quality, and to get efficient optical properties. Without any post thermal treatment, we succeeded in obtaining well-crystallized YAG:Ce nanocrystals (30–200 nm), displaying typical PL properties of YAG:Ce with a maximal emission at 550 nm. The pristine 100 nm-sized YAG:Ce nanoparticles present an internal quantum yield of about 40 ± 5%. In situ X-ray absorption near edge spectroscopy demonstrates the presence of Ce ~(4+) in nanocrystals elaborated at high temperature, resulting from the oxidation of Ce ~(3+) during the crystallization process.
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