Development of fine-powder processing route for nitride phosphors for white LEDs

Abstract

In the last few years, highly covalent Si₃N₄-based oxynitrides （SiAlONs） have been developed as an important family of phosphor host materials due to their great potentials for white LED applications. Generally, SiAlON-based nitride phosphors are synthesized by the reaction sintering of Si₃N₄, AlN, and other constituent metal oxide or nitride raw powders under pressured N₂ atmosphere at ～1600–2000^oC, followed by the postsynthesis grinding step to pulverize crude reaction products. This obvious low manufacturability is a major obstacle to their widespread use in LED applications, triggering the intense investigations for developing more sophisticated processing techniques.

In this regard, the present authors have developed the gas-reduction–nitridation （GRN） method, which enables direct synthesis of fine SiAlON powders from the multicomponent oxide system by using an NH₃–CH₄ gas mixture as a reduction–nitridation agent. The Ca-α-SiAlON powder produced by the GRN is characterized by high phase purity, nonaggregated fine particle morphology, and very low impurity absorption throughout emissive regions, all of which meet the demands for phosphor applications.