Fine yellow α-SiAlON:Eu phosphors for white LEDs prepared by the gas-reduction-nitridation method

Yellow-emitting α-SiAlON:Eu2+ phosphors were synthesized by the gas reduction and nitridation of a homogeneous oxide precursor in a CaO-Al2O3-SiO2-Eu2O3 system at 1400-1450 °C using an NH3-CH4 mixture gas as a reduction-nitridation agent. The precursor was prepared by a sol-gel process using a low-cost nitrate, tetraethyl orthosilicate and citric acid as the starting materials. The effects of reaction parameters such as heating rate, temperature, holding time and CH4 content on the composition, microstructure and photoluminescence of the prepared powders were investigated. Nearly single-phase α-SiAlON was successfully synthesized by the one-step gas reduction and nitridation without the need for post-annealing at a higher temperature. The prepared powders consisted of relatively well-dispersed and uniform crystals with a hexagonal shape. The photoluminescence spectra of Eu-doped Ca-α-SiAlON phosphors excited by near-ultraviolet or blue light showed a broad, yellow emission band at 500-700 nm, which agrees well with that obtained from phosphors prepared by the conventional solid-state reaction.