Twofold advantage of gas bubbling for the advanced solvothermal preparation of efficient YAG:Ce nanophosphors

With the goal of controlling the oxidation state of cerium ions in Ce-doped Y3Al5O12 nanocrystals (YAG:Ce), different gases (Ar/H2, O2, Ar) were bubbled inside the solution of precursors and solvent prior to the solvothermal synthesis. As assessed by X-ray absorption spectroscopy, this protocol modifies the Ce3+ : Ce4+ ratio in YAG:Ce nanocrystals, although it does not allow complete prevention of the Ce3+ → Ce4+ oxidation. In addition, gas bubbling strongly influences the size and crystal quality of YAG:Ce nanocrystals, as evidenced by X-ray diffraction and transmission electron microscopy. Indeed, the presence of bubbles in the precursor solution induces heterogeneous nucleation, leading to an earlier nucleation step. This favors the growth and the high crystallinity of YAG:Ce nanocrystals leading to record iQY at around 52% for 60 nm sized nanocrystals and 66% for those of 200 nm.