Crystal structure, luminescence properties, energy transfer and thermal properties of a novel color-tunable, white light-emitting phosphor Ca9-x-yCe(PO4)7:xEu2+,yMn2.

A series of Ca9-x-yCe(PO4)7:xEu2+,yMn2+ phosphors were synthesized by a high-temperature solid-state reaction method. The as-prepared samples were characterized by XRD and EDX measurements, which showed that Eu2+ and Mn2+ could be efficiently doped into the host. Ce3+ acts concurrently as activator and sensitizer in Ca9Ce(PO4)7, and the energy transfer mechanisms between Ce3+/Eu2+ and Ce3+/Mn2+ in Ca9Ce(PO4)7 were validated and proven to be a resonant type via dipole-quadrupole and dipole-dipole interactions, respectively. Besides, there is also energy transfer from Eu2+ to Mn2+ ions. The host, Ca9Ce(PO4)7, emits blue-white light and Ca9Ce(PO4)7:xEu2+,yMn2+ phosphors emit blue-green through white to orange-red light under near-ultraviolet radiation as a result of tuning the ratio of Eu2+/Mn2+. Ca9Ce(PO4)7:0.04Eu2+,0.08Mn2+ emits white light with CIE coordinates (0.333, 0.310), a CCT of 5446 K, and a high CRI of 81. The energy transfer efficiency between Ce3+ and Mn2+ increases significantly with temperature. These results reveal that Ca9Ce(PO4)7:Eu2+,Mn2+ may be a potential candidate for white light-emitting phosphors.