Observation on long afterglow of Tb3+ in CaWO4

Abstract The Tb 3+ doped CaWO 4 phosphors are synthesized via high temperature solid state reaction. The X-ray diffraction shows that small amount of Tb 3+ does not have a significant influence on the structure of CaWO 4 . A broad absorption band of the WO 4 2− group is observed from photoluminescence and the energy transfer from WO 4 2− group to Tb 3+ ions induces the f–f transition. The cross-relaxation between two adjacent Tb 3+ ions weakens 5 D 3 – 7 F j transitions and enhances the 5 D 4 – 7 F j transitions, leading to a green long afterglow of the phosphors. The thermoluminescence curves centered around 75 °C reveal the trap depth for afterglow generation is about 0.74–0.77 eV. The optimum Tb 3+ concentration for afterglow properties is about 1%. A deep hole trap is induced when Tb 3+ concentration exceeds 1% and it suppresses the thermoluminescence and the decay properties.