The evolution and role of NH ₄ Cl flux used to synthesize Sr ₂ SiO ₄: Dy ³⁺ phosphor by solid-state reaction method

Two different Sr₂SiO₄:Dy³⁺ phosphors were successfully synthesized at 1000°C for 4 h using NH₄Cl or SrCl₂ as the flux, respectively. The luminescence intensity of Sr₂SiO₄:Dy³⁺ was enhanced 60 times by the addition of 5 wt% NH₄Cl. The phase evolution and photoluminescence (PL) properties of the phosphors were investigated by the calculation of phase equilibrium and the analysis of TG/DSC, XRD, SEM, and PL. The role of NH ₄Cl was proved to be attributed to the formation of SrCl₂ at ~300°C. The flux NH₄Cl or SrCl₂ lowered the decomposition temperature of carbonate and promoted the preferential formation of α' phase in the solid-state reaction through accelerating the kinetics of the formation of Sr₂SiO₄ by enhancing diffusion with more liquid phase.