Phase purity and luminescence properties of fine Ca-α-SiAlON:Eu phosphors synthesized by gas reduction nitridation method

This paper reports a simple, inexpensive, and efficient synthetic route to Ca-α-SiAlON: Eu2+ -based yellow phosphors for white light-emitting diodes. Through direct gas reduction and nitridation of the homogeneous oxide precursor of CaO- Al2 O3 - SiO2 - Eu2 O3, fine Ca-α-SiAlON: Eu2+ phosphors were obtained by one-step firing at 1450°C for 4 h in the flowing NH3 and CH4 (1.0 vol %) mixture gas. The dependence of the structural characterization and optical properties on the overall composition of the host lattice has been investigated. A nearly single-phase Ca-α-SiAlON can be synthesized by controlling the overall composition of the host lattice at m=2.0 and n=0-0.2. The strongest luminescence is achieved at about m=3.5 and n=0-0.2. Further improvement of the powder characteristics was attained by post heat-treatment at 1700°C for 2 h under 5 atm of N2 by gas-pressure sintering. The post-treated powders showed a pure α-SiAlON phase at 1.0m3.5. The Ca-α-SiAlON:Eu phosphor exhibits a high crystallinity, high luminescence intensity, high quantum efficiency, and very low thermal quenching, which is better than those prepared by the conventional solid-state reaction.