Two different Sr2SiO4:Dy3+ phosphors were successfully synthesized at 1000 degrees 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 NH4Cl was proved to be attributed to the formation of SrCl2 at 300 degrees C. The flux NH4Cl or SrCl2 lowered the decomposition temperature of carbonate and promoted the preferential formation of a' phase in the solid-state reaction through accelerating the kinetics of the formation of Sr2SiO4 by enhancing diffusion with more liquid phase.