Novel high color purity phosphors Sr9Mg1.5(PO4)7: Sm3+, R+ (R = Li, Na, K): Crystal structure, luminescence and thermal quenching property investigation

A series of novel orange-red phosphors Sr9Mg1.5(PO4)(7): xSm(3+) were synthesized by high temperature sintering method. Rietveld refinement, X-ray diffraction patterns, photoluminescence spectra, decay times and luminescence spectra showing thermal quenching were measured and investigated in detail. The mechanism of interaction for energy transfer, CIE chromaticity coordinates and color purity of the phosphors were studied and discussed, too. According to the Rietveld refinement, the coordination numbers of Sr2+ were reconfirmed based on the refined structure for the first time. Moreover, it was found that under near-ultraviolet excitation, Sr9Mg1.5(PO4)(7): xSm(3+) exhibited an intense orange-red emission centering at 598 nm and 650 nm which can be assigned to (4)G(5/2) to H-6(7/2) and H-6(9/2) energy level transitions of Sm3+, respectively. The CIE chromaticity coordinates of Sr9Mg1.5(PO4)(7): 0.2Sm(3+) was (0.6066, 0.3923) with outstanding color purity of 98.8%. The sample also exhibited good thermal quenching properties with the remained 70% emission intensity at 150 degrees C compared with that at ambient temperature. Furthermore, in order to further improve the luminescent intensity and the thermal stability, Li+, Na+ and K+ were incorporated into Sr9Mg1.5(PO4)(7):0.2Sm(3+) as the compensator charges. Among all the samples with compensator charges, Sr9Mg1.5(PO4)(7):0.2Sm(3+), 0.2Na(+) presented the highest emission intensity and best temperature quenching properties because of the similar radius of Na+ and Sr2+. The improved and linear thermal stability and strong luminescence intensity suggested that Sr9Mg1.5(PO4)(7):0.2Sm(3+), 0.2Na(+) has a potential use in solid-state lighting.