Abstract
In a series of (Ca(2-x/2-y)Eu(y)□(x)(/2))(Si(1-x)P(x))O₄ (x = 0.06, 0.02 ≤ y ≤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(3+) to Eu(2+). In the red-emitting (Ca(1.95)Eu(3+)(0.02)□(0.03))(Si(0.94)P(0.06))O(4+δ) phosphor, the highest PL intensity exhibited when it was annealed at 1773 K. On the other hand, in the green-emitting (Ca(1.95)Eu(2+)(0.02)□(0.03))(Si(0.94)P(0.06))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(2+) 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'(L), which occurred by heat treatment, and the amount of doped Eu ions.