Luminescence properties of Eu~(3+) ions in phosphate-based bioactive glasses

摘要

Eu_2O_3-doped phosphate-based bioactive glasses have been prepared by varying the calcium/potassium to phosphate ratio and their luminescence properties have been studied through absorption and emission spectra and decay rate analysis. Second and fourth rank crystal-field (CF) parameters and the CF strength parameters have been calculated by assuming the C_(2v) symmetry for Eu~(3+) ions in the present glasses. Judd-Ofelt analysis has been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak-stimulated emission cross-sections for ~5D_0 ->~7F_J (J = 0-4) transitions. The relative luminescence intensity ratio of ~5D_0 ->~7F_2 and ~5D_0 ->~7F_1 transitions has been evaluated to estimate the local site symmetry around Eu~(3+) ions. The observed ~5D_0 ->~7F_0 transition for higher calcium content indicates two distinct sites for Eu~(3+) ion. Decay rates for the ~5D_0 level of Eu~(3+) ions in these glasses have been measured by monitoring the ~5D_0 ->~7F_2 transition. The lifetimes of the ~5D_0 level are found to decrease with increase in calcium contents.