Synthesis and Photoluminescence Properties of Yellow γ-Ca₂SiO_4-δN_δ:Ce³⁺,Ga³⁺ Phosphors

γ-Ca2SiO4:Ce3+ phosphors were successfully synthesized through the synergistic stabilization effect of Ga3+ and N3−. Ga3+ ions effectively promote β → γ phase transformation, compared to the effect of the conventionally used Al3+ ions. When Ga2O3 was used in the raw materials as the source of Ga3+, the optimum amount of Ga3+ ions was 1%, which decreased to 0.75% when GaN was used for providing the Ga3+ ions in the produced phosphors. The phenomenon of "dusting" occurred, ascribed to the fact that the phosphor was in the form of a fine soft powder, owing to the volume increase and the angular unit cell change during phase transformation. The produced γ-Ca2SiO4-δNδ:Ce3+,Ga3+ phosphors exhibited an intense wide yellow emission band, with a peak at 565 nm, upon 450 nm excitation, which is attributed to the 4f05d1→4f1 transitions in the Ce3+ ions, and a good thermal quenching, with the photoluminescence intensity of γ-(Ca0.995Ce0.005)2Si0.9925Ga0.0075O4-δNδ at 150°C being ∼76% of the intensity measured at room temperature.