Luminescence Investigation of Eu‐Activated Sr 5 (PO 4 ) 2 SiO 4 Phosphor by Combustion Synthesis

Eu‐activated Sr 5 (PO 4 ) 2 SiO 4 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 Sr 5 (PO 4 ) 2 (SiO 4 ) host is found to be about 7.3 eV from the VUV excitation spectra. The replacement of the (PO 4 ) 3− anionic network by the more covalent (SiO 4 ) 4− in apatite results in red‐shift of the Eu 2+ emission giving rise to the two broad emission bands with peaks at 495 and 560 nm corresponding to the 4 f 6 5 d 1 →4 f 7 ( 8 S 7/2 ) transition of Eu 2+ . Together with the Eu 2+ luminescence, the unusual emission line (572 nm) due to the 5 D 0 → 7 F 0 transition of Eu 3+ is observed in Sr 5 (PO 4 ) 2 SiO 4 prepared by the combustion synthesis. The temperature‐dependent luminescence and decay curves of the Eu 2+ and Eu 3+ ions are investigated from 10 to 300 K. The crystallographic sites and reduction mechanism for Eu 2+ and Eu 3+ in the Sr 5 (PO 4 ) 2 SiO 4 lattice are discussed. The Eu 3+ ions doped in Sr 5 (PO 4 ) 2 (SiO 4 ) are suggested to occupy MII sites with the charge compensation related to the interstitial oxygen O i : 2Sr 2+ →2Eu 3+ +O″ i . The unusual emission line due to the 5 D 0 → 7 F 0 transition of Eu 3+ in Sr 5 (PO 4 ) 2 (SiO 4 ) is attributable to the charge‐compensating oxide ion and an abnormal crystal field strength experienced by the Eu 3+ ions.