Optical absorption and photoluminescence studies of Eu3+-doped phosphate and fluorophosphate glasses

Phosphate (P2O5+K2O+BaO+Al2O3+Eu2O3) and fluorophosphate (P2O5+K2O+BaO+BaF2+Al2O3+Eu2O3) glasses with different Eu3+ ion concentrations have been prepared and characterized through optical absorption, photoluminescence and decay times. An intense red luminescence is observed from the 5D0 emitting level of Eu3+ ions in these glasses. The relative luminescence intensity ratio of 5D0→7F2→5D0→7F1 transitions has been evaluated to estimate the local site symmetry around the Eu3+ ions. The emission spectra of these glasses show a complete removal of degeneracy for the 5D0→7F1 and 5D0→7F2 transitions. Second and fourth rank crystal-field (CF) parameters have been calculated together with the CF strength parameter by assuming the C2v symmetry for the Eu3+ ions in both the phosphate and fluorophosphate glasses. Judd-Ofelt parameters have been evaluated from the luminescence intensity ratios of 5D0→7FJ (J=2, 4 and 6) to 5D0→7F1 transitions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross-sections for the 5D0→7FJ transitions. Decay curves of the 5D0 level of Eu3+ ions in these two Eu3+:glass systems have been measured by monitoring the 5D0→7F2 transition (611 nm) at room temperature. The experimental lifetime of the 5D0 level in the title glasses is found to be higher than Eu3+-doped niobium phosphate glasses. The analysis indicates that the lifetime of the 5D0 level is found to be less sensitive to the Eu3+ ion concentration and addition of BaF2 has no significant effect on the optical properties of Eu3+-doped phosphate glasses.