Synthesis and photoluminescence of Eu2+ by co-doping Eu3+ and Cl− in Sr2P2O7 under air atmosphere

Abstract A novel phosphor Sr 2 P 2 O 7 co-doped with europium ion and chlorine ion was firstly synthesized by solid state reaction under air atmosphere. Its properties were systematically analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectra. The introduction of chlorine into the system was helpful and necessary to Eu 3+ substitute Sr 2+ site and subsequently to reduce Eu 3+ to Eu 2+ , XPS results confirmed that some amount of Eu 3+ ions could be reduced to Eu 2+ ions under air atmosphere at high temperature. The reduction tendency of Eu 3+ depends not only on the doping Cl − content, but also on the sintering temperature and time. Photoluminescence spectra also revealed that europium ions were present in divalent as well as trivalent oxidation states, the emission peak at 415 nm is ascribed to the typical 5d–4f transition of Eu 2+ , 592 nm and 613 nm assigned to the characteristic transitions of 5 D 0 – 7 F 1,2 of Eu 3+ . Such abnormal reduction was attributed to the electronegative defects formed by nonequivalent substitution of Eu 3+ on the Sr 2+ sites in the investigated phosphors.