The Effect of Heat Treatment on the Emission Color of P-Doped Ca₂SiO₄ Phosphor.

In a series of (CaEu□)(SiP)O₄ ( = 0.06, 0.02 ≤ ≤0.5), various color-emitting phosphors were successfully synthesized by a solid-state reaction. These phosphors were characterized by photoluminescence (PL) spectroscopy, X-ray powder diffractometry, transmission electron microscopy, and X-ray absorption fine structure spectroscopy. We evaluated the effect of heat treatment on PL properties with various annealing temperatures at 1373-1773 K for 4 h before/after reduction treatment from Eu to Eu. In the red-emitting (CaEu□)(SiP)O phosphor, the highest PL intensity exhibited when it was annealed at 1773 K. On the other hand, in the green-emitting (CaEu□)(SiP)O₄ phosphor, the highest PL intensity was realized when it was annealed at 1473 K and consequently treated under a reductive atmosphere. With increasing annealing temperature, the emission peak wavelength steadily decreased. Furthermore, with increasing Eu content, the emission peak wavelength increased, with the color of emitting light becoming yellowish. Thus, the PL properties of the phosphors were affected by both the structural change from β to α', which occurred by heat treatment, and the amount of doped Eu ions.