Luminescence and energy transfer in La2O3–Nb2O5–B2O3:M3+ (M=Bi, Eu, Dy) glasses

The luminescence and energy transfer processes in La2O3–Nb2O5–B2O3:M3+ (M=Bi, Eu, Dy) glasses were investigated using luminescence spectroscopy (excitation and emission, down to 4.2 K) and decay time measurements at room temperature. The observation of niobate luminescence implies a considerable degree of short- and intermediate-range order in these glasses. Energy transfer from the niobate groups to the lanthanide ions was observed for Eu3+, but not for Dy3+, suggesting that the energy transfer process occurs to the charge-transfer state of the Eu3+ ion, rather than to its f-levels. Inter-Eu3+ energy transfer was negligible in the concentration range investigated (up to 3 mol%). In contrast, cross-relaxation processes between Dy3+ ions were active at concentrations as low as 0.5 mol%. In the Bi3+ doped glasses the energy transfer was observed from the Bi3+ excited levels to the oxygen deficient niobate groups.