Structure, bandgap, photoluminescence evolution and thermal stability improved of Sr replacement apatite phosphors Ca10-xSrx(PO4)6F2:Eu2+ (x=4, 6, 8)

A series of Sr-replaced solid solution Ca10-xSrx(PO4)(6)F-2:Eu2+ (x = 4, 6, 8) phosphors with apatite structure were engineered and synthesized successfully via the solid-state reaction. The crystal structure, bandgap and photoluminescence properties of the Ca10-xSrx (PO4)(6)F-2:Eu2+(x = 4, 6, 8) phosphors were investigated in detail. With the increase of Sr concentration, the bandgap gets narrower and the volume of crystal becomes larger. The existence of oxygen-vacancy-related defect levels in the bandgap and the bandgap reduction caused by these levels were verified by DFT calculated and experiment results. The emission spectra of samples show blue shift from 459 nm to 447 nm. Simultaneously, all of the samples have broad absorption ranging from 240 nm to 450 nm and the crests of these spectra show little blue shift from 343 nm to 337 nm. The thermal stabilities of these samples show obvious improvement (55.01%-68.24% at 150 degrees C) with the increase of Sr concentration, which indicates that the solid solution design can serve as an effective way to improve the thermal stability of apatite phosphors. In addition, a white LED device has been manufactured by connecting a 380 nm UV chip with a blend of Ca4Sr6(PO4)(6)F-2:Eu2+, (Sr,Ba)SiO4:Eu2+ and CaAISiN(3):Eu2+. The LED device shows warm white light with low color temperature (3728 K) and high color rendering index (90.21). Our results provide a practical basis to engineer and develop Eu2+-doped novel phosphors.