Crystallization and fluorescence properties of Ce:YAG glass-ceramics with low SiO2 content

Ce3+ doped YAG (Ce:YAG) glass-ceramics with 20 mol% SiO2 were fabricated by the method of amorphous sintering followed by controlled crystallization (ASCC). An investigation on the crystallization process of as-sintered glasses revealed that surface crystallization occurred first and YAlO3 (YAP) was precipitated as the main crystalline phase; then bulk crystallization continued inside these glasses and YAP phase transited to YAG. The phase transition from YAP to YAG could be promoted by an inert atmosphere instead of reductive one and by the increase of the crystallization temperature and holding time. By combining the Ce:YAG glass-ceramics with a blue-emitting InGaN chip, white LEDs with a relatively high color rendering index of 80.3 and low color temperature of 5098 K were produced. Their luminous efficacy decreased with the increasing annealing temperatures, which was probably caused by the degradation of transparency.