The electronic structure and luminescence properties of Ce3+ doped Sr10[(PO4)5.5(BO4)0.5]BO2 under UV/VUV and X-ray excitation

Abstract

The apatite related compound Sr10[(PO4)5.5(BO4)0.5]BO2 (SrBPO) doped with Ce3+ was synthesized via solid state reaction method. Undoped SrBPO shows blue-green emission under ultraviolet (UV) and X-ray excitation due to the defects in the host. When excited by vacuum ultraviolet–ultraviolet (VUV–UV) light or X-ray, Ce3+ doped SrBPO shows a broad emission band peaking at 450nm originating from 5d–4f transition of Ce3+ and defects in the host. The phosphor exhibits strong excitation bands in UV range and a weak broad excitation band in VUV region. The site occupation of Ce3+ was proposed based on fluorescence decay curves. Electronic structure shows the compound is an indirect semiconductor with a band gap of 3.04eV. The extremely small density of states of [PO4]3− or [BO4]5− group near Fermi level or in the conduction band is a possible origin of the weak excitation band in the VUV range. A possible mechanism was proposed to explain the luminescence properties observed.