Site-occupancy, luminescent properties and energy transfer of a violet-to-red color-tunable phosphor Ca10Li(PO4)7: Ce3+, Mn2+

A series of color-tunable phosphors Ca10Li(PO4)7: Ce3+, Mn2+ were synthesized by high-temperature solid-state reaction. Site occupancy of Ce3+ and Mn2+ in Ca10Li(PO4)7 and corresponding luminescent properties were systemically studied. Rietveld refinement results indicate that the Ce3+ ions are preferred to occupy 7-cooridnated M1 and M3 sites, and Mn2+ ions are mainly occupying distorted octahedral M5 sites, which results in Ce3+ violet emission at 370 nm and Mn2+ red emission at 640 nm. The intensity of Mn2+ red emission is greatly enhanced through efficient Ce3+-Mn2+ energy transfer (ηET=94%). The critical distance and corresponding mechanism of Ce3+-Mn2+ energy transfer was found to be ~11 Å and dipole-quadrupole interaction, respectively. The emitting colors of Ca10Li(PO4)7: Ce3+, Mn2+ phosphors can be tuned from violet through pink to red by adjusting the Ce3+/Mn2+ ratio. The composition-optimized red phosphor Ca10Li(PO4)7: 0.05Ce3+, 0.09Mn2+ exhibits excellent thermal stability at high temperature (~100% at 160 °C).