Radiation induced defects in BaBPO5:Ce and their role in thermally stimulated luminescence reactions: EPR and TSL investigations

Defect centers induced by gamma irradiation in Ce doped BaBPO5 were investigated using EPR spectroscopy. From EPR studies, three phosphorous centered radicals were characterized on the basis of observed 31P hyperfine splitting and g values as PO42-, PO22- and PO44- radicals. In addition to this, two types of boron oxygen hole centers (BOHC) and O− were also formed at room temperature. An intense broad signal in sample annealed in argon (g⊥ = 1.9258 and g‖ = 1.8839) was assigned to Ce3+ ions associated with the electron trapped at anion vacancy or nearby lattice defect. TSL studies showed two glow peaks, a relatively weaker one at 425 K and an intense one at 575 K. Spectral studies of the TSL glow peaks have shown that Ce3+ ion acts as emission center. From the temperature dependence of the EPR spectra of gamma irradiated samples, the glow peaks at 425 K and 575 K were attributed to thermal destruction of PO42-/O− and BOHC, respectively, by trapping of electrons from elsewhere. The energy released in electron hole recombination process is used for the excitation of Ce3+ ions resulting in these glow peaks at 425 K and 575 K. The spectral studies of the TSL glow peaks have shown emission at 330 nm indicating Ce3+ acts as the luminescent centre. The trap depth and the frequency factor for the 425 K and 575 K peaks were determined using different heating rates method.