Tunable luminescence properties and energy transfer of single-phase Ca4(PO4)2O: Dy3+, Eu2+ multi-color phosphors for warm white light

The novel Ca4-x (PO4)(2)O: xDy(3+) and Ca4-x-y (PO4)(2)O: xDy(3+), yEu(2+) multi-color phosphors were synthesized by traditional solid-state reaction. The crystal structure, particle morphology, photoluminescence properties and energy transfer process were investigated in detail. The X-ray diffraction (XRD) results demonstrate that the products showed pure monoclinic phase of Ca-4(PO4)(2)O when x < 0.1. The scanning electron microscopy (SEM) indicated that the phosphors were grain-like morphologies with diameters of similar to 3.7-7.0 mu m. Under excitation of 345 nm, Dy3+-doped Ca-4(PO4)(2)O phosphors showed multi-color emission bands at 410, 481 and 580 nm originated from oxygen vacancies and Dy3+. Interestingly, Ca-4(PO4)(2)O: Dy3+, Eu2+ phosphors exhibited blue emission band at 481 nm and broad emission band from 530 to 670 nm covering green to red regions. The energy transfer process from Dy3+ to Eu2+ was observed for the co-doped samples, and the energy transfer efficiency reached to 60% when Eu2+ molar concentration was 8%. In particular, warm/cool/day white light with adjustable CCT (2800-6700 K) and high CRI (R (a) > 85) can be obtained by changing the Eu2+ co-doping contents in Ca-4(PO4)(2)O: Dy3+, Eu2+ phosphors. The optimized Ca-3.952(PO4)(2)O: 0.04Dy(3+), 0.008Eu(2+) phosphor can achieve the typical white light with CCT of 4735 K and CRI of 87.