New whitlockite-type structure material Sr9Y(PO4)7 and its Eu2+ doped green emission properties under NUV light

This work is to synthesize a new whitlockite type polycrystal Sr9Y(PO4)7 by traditional solid state reaction and investigate its rare earth Eu2+ doped luminescent properties. Sr9Y(PO4)7 is designed according to a typical matrix Sr9Fe(PO4)7. It is an equivalent replacement by Y3+ at the same position of the Sr9Fe(PO4)7. The new type host Sr9Y(PO4)7 and its Eu2+ doped luminescent properties are studied in detail by TEM, SEM, XRD, Retiveld refinement and a variety of fluorescence test. Sr9Y(PO4)7 is a trigonal type crystal belonging to R-3 m (166). There are three kinds of Sr2+ sites in the crystal structure with different environments. Sr2+ has close spatial location and inferior occupancy ratio. After the structure and photo luminescence spectra analysis, Eu2+ can occupy three kinds Sr2+ in this host and emit bright green light peaking at ~523 nm with quantum efficiency 29.1% under NUV excitation. The loose or not tight structure leads to disappointed thermal stability, which the photo luminescence intensity just retains 30% compared with it at room temperature at 150 °C. White LED is fabricated successfully using Sr9Y(PO4)7: Eu2+ material and commercial blue BAM: Eu2+ and red CaAlSiN3: Eu2+ phosphors combining with a UV GaN chip. The chromaticity coordinates and CCT are (0.3372, 0.3418) and 5288 K.