Radiation induced defects in BaBPO_5:Ce and their role in thermally stimulated luminescence reactions: EPR and TSL investigations

摘要

Defect centers induced by gamma irradiation in Ce doped BaBPO5 were investigated using EPR spectros-copy. From EPR studies, three phosphorous centered radicals were characterized on the basis of observed ~(31)P hyperfine splitting and g values as PO_4~(2-), PO_2~(2-) and PO_4~(4-) 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 Ce~(3+) 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 Ce~(3+) 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 PO_4~(2-)/O~- and BOHC, respectively, by trapping of electrons from elsewhere. The energy released in electron hole recombination process is used for the excitation of Ce~(3+) 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 Ce~(3+) 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.