Luminescence Investigation of Eu-Activated Sr5(PO4)2SiO4 Phosphor by Combustion Synthesis
Eu-activated Sr5(PO4)2SiO4 with apatite structure was synthesized by the combustion synthesis. The phase formation and morphology were investigated by X-ray powder diffraction and scanning electron microscopy measurements, respectively. The phosphors were characterized by photoluminescence excitation and emission spectra, and decays. The band gap of Sr5(PO4)2(SiO4) host is found to be about 7.3 eV from the VUV excitation spectra. The replacement of the (PO4)3− anionic network by the more covalent (SiO4)4− in apatite results in red-shift of the Eu2+ emission giving rise to the two broad emission bands with peaks at 495 and 560 nm corresponding to the 4f65d1→4f7(8S7/2) transition of Eu2+. Together with the Eu2+ luminescence, the unusual emission line (572 nm) due to the 5D0→7F0 transition of Eu3+ is observed in Sr5(PO4)2SiO4 prepared by the combustion synthesis. The temperature-dependent luminescence and decay curves of the Eu2+ and Eu3+ ions are investigated from 10 to 300 K. The crystallographic sites and reduction mechanism for Eu2+ and Eu3+ in the Sr5(PO4)2SiO4 lattice are discussed. The Eu3+ ions doped in Sr5(PO4)2(SiO4) are suggested to occupy MII sites with the charge compensation related to the interstitial oxygen Oi: 2Sr2+→2Eu3++O″i. The unusual emission line due to the 5D0→7F0 transition of Eu3+ in Sr5(PO4)2(SiO4) is attributable to the charge-compensating oxide ion and an abnormal crystal field strength experienced by the Eu3+ ions.
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