Novel orange light emitting phosphor Sr9(Li, Na, K)Mg(PO4)7: Eu2+ excited by NUV light for white LEDs

Abstract

A series of novel orange emission Sr9(Li, Na, K)Mg(PO4)7: Eu2+ phosphors under NUV excitation are synthesized successfully by traditional high temperature solid-state reaction. The structure of Sr9(Li, Na, K)Mg(PO4)7 is investigated by High-resolution transmission electron microscopy, selected area electronic diffraction and X-ray powder diffraction Rietveld refinement and the crystal structure of Sr9(Li, Na, K)Mg(PO4)7 was found to be trigonal, belonging to R-3m (166) space group. As a representative, the PL properties of Sr9LiMg(PO4)7: Eu2+ are investigated detail by diffuse reflection spectra, emission spectra, excitation spectra, decay curves and temperature dependence spectra. It can emit orange light peaking at 635 nm with 405 nm excitation. According to structure and photoluminescence (PL) properties analysis, Eu2+ can occupy three kinds of Sr2+ site. The concentration quenching mechanism of Eu2+ could be a d-d interaction luminescence center. It has bad temperature stability properties because of too much co-angle connections in the structure. By tuning weight ratio of blue and orange phosphors, the fabricated white-LEDs using a 405 nm GaN NUV chip combined with a blend of blue phosphor BAM: Eu2+and orange emitting Sr9LiMg(PO4)7: 0.04Eu2+ phosphor driven by 30 mA current can get tunable white light with chromaticity coordinates from (0.3535, 0.3011) and CCT 4287 K to (0.4036, 0.3539) and 3131 K. It demonstrates that Sr9-xEuxLiMg(PO4)7 is a potential orange phosphor matching NUV LED chips to get white light.