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

Abstract

A novel phosphor Sr2P2O7 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 Eu3+ substitute Sr2+ site and subsequently to reduce Eu3+ to Eu2+, XPS results confirmed that some amount of Eu3+ ions could be reduced to Eu2+ ions under air atmosphere at high temperature. The reduction tendency of Eu3+ 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 415nm is ascribed to the typical 5d–4f transition of Eu2+, 592nm and 613nm assigned to the characteristic transitions of 5D0–7F1,2 of Eu3+. Such abnormal reduction was attributed to the electronegative defects formed by nonequivalent substitution of Eu3+ on the Sr2+ sites in the investigated phosphors.