Microstructure of rapidly quenched YAG-based glass–ceramics prepared by aerodynamic levitation

Almost-spherical yttrium aluminum garnet (Y3Al5O12, YAG) was synthesized using an aerodynamic levitator. The formation of crystalline or glass–ceramic depended on the initial mass of the molten droplet. The YAG was devitrified due to partial crystallization, even after rapid quenching, indicating a high tendency for crystallization. The darker spheroid phase nucleated from the Y2O3–Al2O3 melt because of a polyamorphic liquid–liquid phase transition. The optical transparency of YAG increased with increasing Eu3+ content because of the reduced number of micro-sized crystals, which act as a scattering center to visible light. The photoluminescence intensity of the YAG:Eu glass–ceramic was attributed mainly to an electric dipole 5D0→7F2 transition because the Eu3+ in the YAG glass–ceramic is located at sites with low symmetry.