New self-activated eulytite-type compounds of M7Zr(PO4)6 (M = Ca, Sr, Ba)

Eulytite-type orthophosphates M7Zr(PO4)6 (M = Ca, Sr, Ba) were prepared by conventional high temperature solid-state reaction. Sr7Zr(PO4)6 and Ba7Zr(PO4)6 crystallize in the pure eulytite-type phase with cubic space group (I4¯3d). The impurity phase β-Ca3(PO4)2 was inevitably coexisted with the Ca7Zr(PO4)6 phase. The luminescence properties are investigated by UV–VUV excitation and emission spectroscopy and X-ray-excited luminescence (XEL) spectroscopy. The broad excitation and emission bands are observed due to the charge transfer transition from Zr4+ to O2− in M7Zr(PO4)6 (M = Ca, Sr, Ba) eulytite. The characteristics of the phosphors including the luminescence mechanism are explained by Stokes shift, decay curves, and CIE color coordinates. The Sr7Zr(PO4)3 and Ba7Zr(PO4)3 phosphors exhibit unusual spectral features with the emission bands at 470 and 480 nm, respectively. The weak luminescence centered at 495 nm is observed in the Ca7Zr(PO4)6 eulytite with lifetime of 4.67 μs. The unusual self-activated luminescence is discussed on the base of the crystal structure of eulytite.