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.