A Study on Synthesis of SrLu2O4:Eu2+ Red Phosphor and Its Photoluminescence Properties

During the last decades, rare-earth (RE) ion-doped phosphors have received much attention due to their high luminescent properties. For this reason, many studies have been focused on new composition of phosphor with high luminescent properties. Eu3+ doped SrLu2O4, which is a new composition phosphor, has been reported to describe the luminescent properties. Upon excitation with ultraviolet (UV) regions, Eu3+ doped SrLu2O4 phosphor exhibited narrow red emissions due to the 4f-4f transition of Eu3+ ions. Eu3+ ions only can be excited with UV regions and the property of narrow red emission has a limitation to apply for lighting devices such as white light-emitting diodes (WLEDs) due to a low color rendering index (CRI). In this study, we synthesize the Eu2+ doped SrLu2O4 red phosphors with solid-state reaction and characterize the luminescent properties for the first time. For the synthesis of SrLu2O4 at stoichiometric condition, it is hard to synthesize the pure SrLu2O4 phase, because formation of a second phase Lu2O3 were consistently unable to avoid. The pure phase of SrLu2O4 was formed at certain ratio of starting materials and annealing temperature conditions. The mixtures were annealed at various temperatures (1400–1600 °C) for 3 hours under 5% H2/N2 atmosphere in order to reduce Eu3+ to Eu2+. Upon excitation with 450 nm, the synthesized SrLu2O4:Eu2+ phosphors exhibited a strong red emission centered at 610 nm due to the 4f-5d transition of Eu2+ ions (Figure 1). SrLu2O4:Eu2+ phosphors showed highest PL intensity at very low europium doping level, which intensity value was 85% of commercial (Sr,Ca)AlSiN3:Eu2+ (SCASN). In addition, SrLu2O4:Eu2+ phosphors also showed a strong thermal quenching property, which indicated that PL intensity measured at 200 oC was reduced to almost zero per cent of the initial value (25 oC). These high value of PL intensity and strong thermal quenching property can be used as a high potential optical temperature sensor application. Figure 1