Tb-doped YPO4 phosphors: Polyacrylamide gel synthesis and optical properties

Single phase of Tb-doped YPO 4 phosphors with xenotime structure were successfully synthesized via a polyacrylamide gel at different annealing temperatures (650–1050 °C). The crystal structure, thermal behavior and optical properties of the as-synthesized samples were investigated by XRD , TG-DTA, FT-IR, PL, and XPS . The effects of heat treatment on the structure and luminescence properties of samples were discussed. The PL spectra results reveal that the annealing temperature plays a key role in the luminescence properties of products. The samples obtained under 650–850 °C exhibit a strong green emission at 546 nm, attributing to the 5 D 4 - 7 F 5 transition of Tb 3+ , while the samples produced above 850 °C emit dominating blue lines at 381 and 415 nm, corresponding to the 5 D 3 - 7 F 6 and 5 D 3 - 7 F 5 transitions, respectively. The XPS results imply that a part of doping Tb 3+ ions may be oxidized to Tb 4+ on the high-temperature thermal treatment process, which could be the reason for the bluish color of Tb-doped YPO 4 phosphors.