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

The novel Ca 4− x (PO 4 ) 2 O: xDy 3+ and Ca 4− x − y (PO 4 ) 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 (PO 4 ) 2 O when x  < 0.1. The scanning electron microscopy (SEM) indicated that the phosphors were grain-like morphologies with diameters of ~ 3.7–7.0 μm. Under excitation of 345 nm, Dy 3+ -doped Ca 4 (PO 4 ) 2 O phosphors showed multi-color emission bands at 410, 481 and 580 nm originated from oxygen vacancies and Dy 3+ . Interestingly, Ca 4 (PO 4 ) 2 O: Dy 3+ , Eu 2+ 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 Dy 3+ to Eu 2+ was observed for the co-doped samples, and the energy transfer efficiency reached to 60% when Eu 2+ 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 Eu 2+ co-doping contents in Ca 4 (PO 4 ) 2 O: Dy 3+ , Eu 2+ phosphors. The optimized Ca 3.952 (PO 4 ) 2 O: 0.04Dy 3+ , 0.008Eu 2+ phosphor can achieve the typical white light with CCT of 4735 K and CRI of 87.