Study of frequency upconversion in Yb3+/Eu3+ by cooperative energy transfer in oxyfluoroborate glass matrix

Oxyfluoroborate glass co-doped with Eu and Yb ions has been prepared and characterized for its optical properties through photoluminescence, absorption and lifetime measurements. An intense red upconversion is observed from the D-5(0) level of Eu3+ ions through energy transfer from Yb3+ to Eu3+ ion when excited with 980 nm. The Judd-Ofelt parameters have been evaluated to estimate the local site symmetry around the Eu3+ ions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and stimulated emission cross-sections for the D-5(0)-F-7(J) transitions. Decay of excitation of the D-5(0) level has been measured by monitoring the (D0F2)-D-5 transition (613 nm) at room temperature. Quantum efficiency for this transition is found to be 73%. We also monitored the effect of temperature on the fluorescence emission of Eu3+.