Synthesis of Ca-α-SiAlON phosphors by a mechanochemical activation route

Fine Eu2+-doped Ca-α-SiAlON phosphors have been synthesized by a novel mechanochemical activation route from stoichiometric mixtures of β-Si3N4, AlN, Al2O3, CaO and Eu2O3. Mechanical milling mostly transformed the starting powder mixture into an amorphous phase that contained a large number of well-dispersed nanocrystalline β-Si3N4 grains. Homogeneity of elements at the atomic level was achieved in amorphous phase. The formation mechanism of α-SiAlON grains in unmilled powders was through a solution-diffusion-reprecipitation process, leading to an inhomogeneous distribution of Eu2+ ions in the host phase. Mechanical activation significantly promoted the reaction among the starting powders during post-annealing, and α-SiAlON grains composed of nanocrystals with the intended composition formed directly through rapid precipitation from the homogeneous metastable amorphous phase. This novel thermodynamically unfavorable approach leads to the homogeneous distribution of Eu2+ in α-SiAlON crystals resulting in improved photoluminescence. The mechanochemical activation route is expected to be applicable to the synthesis of a wide range of nanosized (oxo)nitridosilicate phosphors with improved homogeneity and photoluminescence efficiency.