Gamma radiation-induced photoluminescence in calcium phosphate glass and inhibiting effect from copper

Abstract

The influence of gamma-ray irradiation on the optical properties of 50P2O5–30CaO–20Na2O glass and quaternary ones prepared with [CuO]/[Na2O] molar ratios of 0.1, 0.7 and 1.5 at fixed [P2O5]/[CaO] is reported. The glasses prepared by melting were subjected to 100 kGy Co-60 gamma ray irradiation and studied by optical transmission and photoluminescence (PL) spectroscopy. The gamma-irradiated 50P2O5–30CaO–20Na2O ternary developed a ruby-red color and showed absorption features around 425 and 500 nm attributed to oxygen hole centers. The quaternary with [CuO]/[Na2O] molar ratio of 0.1 merely showed a weak absorption feature around 425 nm, whereas the highest molar ratios did not show significant differences relative to the pristine. Analyses of band gap and Urbach energies were made to aid in evaluating radiation-induced changes. Further, the irradiated copper-free glass exhibited a distinct blue luminescence band around 415 nm (not observed prior). It was most favorably excited in the UV at 265 nm, suggesting a phosphorus electron center at its origin. Its decay kinetics appeared relatively slow with a first-order exponential decay with lifetime of 4412 (±4) μs. Conversely, such emission was not detected for the copper-containing glasses, which instead exhibited PL properties comparable to the unirradiated counterparts. Finally, the effect of heat treatment after the gamma ray exposure was evaluated. The radiation-induced color centers showed a bleaching effect whereas the new PL vanished thus supporting the defects-related origin.