Optical transitions of Dy3+ in tellurite glass: observation of upconversion

Dy3+ doped tellurite glasses were prepared and its optical absorption, fluorescence and upconversion have been studied. The absorption data has been used to calculate the Judd–Ofelt parameters, oscillator strengths along with transition probability, branching ratio, etc. The lifetime of the F 9 / 2 4 level is found to be 0.66 ms for 1.0 mol% of Dy3+ doped in tellurite glass. NIR to visible upconversion has been observed at room temperature. The increase in upconversion luminescence at lower temperature indicates that upconversion is not due to a thermally activated process. The quantum efficiency of the F 9 / 2 4 → H 13 / 2 6 transition is found to be ∼0.17 and the upconversion efficiency is ∼0.022. The strong dependence of the upconversion efficiency on the Dy3+ concentration reveals that the upconversion is due to energy transfer interaction.