Effect of ZnO as modifier on up and downconversion properties of Ho3+/Yb3+ doped tellurite glasses

Optical absorption and photoluminescent properties of Ho3+/Yb3+ co-doped tellurite and zinc tellurite glasses are investigated. The effect of zinc oxide as a modifier on the luminescence properties of above mentioned samples has been explored. Two intense upconversion emission bands centered at 546 (5F4 + 5S2 → 5I8) and 660 nm (5F5 → 5I8) are observed on excitation with 976 nm diode laser. Zinc oxide acts as a quencher for 976 nm excited upconversion emission. The up and downconversion emission spectra are recorded with 532 nm excitation source also. In this case zinc oxide improves the up and downconversion emissions. A large enhancement in upconversion intensity has been observed when Ho3+ ion is co-doped with Yb3+ ion. The dependence of upconversion intensities on excitation power and on temperature has also been studied. The power dependence study shows a quadratic dependence of the fluorescence intensity on the excitation power while a decrement in emission intensity of all the transitions at different rates with increase in temperature is observed in temperature dependence study. The possible mechanisms are also discussed in order to understand the upconversion and energy transfer processes.