New Series of Red-Light Phosphor Ca9−xZnxGd0.9(PO4)7:0.1Eu3+ (x = 0–1)

In this study, a new series of phosphors, Ca_9−xZn_xGd_0.9(PO₄)₇:0.1Eu³⁺ (x = 0.00–1.00, step dx 0.05), was synthesized, consisting of centro- and non-centrosymmetric phases with β-Ca₃(PO₄)₂-type structure. Crystal structures with space groups R3c (0.00 ≤ x < 0.35) and R3¯c (x > 0.8) were determined using X-ray powder diffraction and the method of optical second harmonic generation. In the region 0.35 ≤ x ≤ 0.75, phases R3c and R3¯c were present simultaneously. Refinement of the Ca₈ZnGd(PO₄)₇ crystal structure with the Rietveld method showed that 71% of Gd³⁺ ions are in M3 sites and 29% are in M1 sites. A luminescent spectroscopy study of Ca_9−xZn_xGd_0.9(PO₄)₇:0.1Eu³⁺ indicated the energy transfer from the crystalline host to the Gd³⁺ and Eu³⁺ luminescent centers. The maximum Eu³⁺ luminescence intensity corresponds to the composition with x = 1.