Structure and photoluminescence properties of a novel apatite green phosphor Ba5(PO4)2SiO4:Eu2+ excited by NUV light.

A novel apatite mineral of Ba5(PO4)2SiO4 was synthesized successfully using a traditional high temperature solid-state reaction. Its structure was determined by high-resolution transmission electron microscopy, fast Fourier transform, energy dispersive X-ray spectroscopy, and X-ray powder diffraction Rietveld refinement, and this was found to be a hexagonal crystal system with the space group attributed to P63/m (176). Moreover, a series of Eu2+ doped Ba5(PO4)2SiO4 phosphors were investigated. The photoluminescence (PL) properties of Ba5(PO4)2SiO4:Eu2+ were investigated in detail by density functional theory calculations, diffuse reflection spectra, emission-excitation spectra, decay curves, and temperature dependence spectra. It can emit green light peaking at ∼515 nm under 405 nm NUV excitation with quantum efficiency 31.89%. According to structure and photoluminescence (PL) property analysis, Eu2+ can occupy two kinds of Ba2+ site. The concentration quenching mechanism of Eu2+ could be a d-d interaction luminescence center. It has poor temperature stability properties because of too much temperature-dependent electron-phonon interaction at high temperature. Fabricated white-LEDs using a 405 nm GaN NUV chip combined with a blend of RGB phosphors: CaAlSiN3:Eu2+, Ba5(PO4)2SiO4:1%Eu2+ and BAM:Eu2+, driven by 30 mA current can get warm-white light with chromaticity coordinates (0.355, 0.342) and correlated color temperature (CCT) 4561 K. This demonstrates that Ba5(PO4)2SiO4:Eu2+ is a potential green phosphor matching NUV LED chips to get white light.