Infrared to visible up-conversion study for erbium-doped zinc tellurite glasses

Optical absorption and photoluminescence properties of Er³⁺-doped 70TeO₂-30ZnO glass are investigated. Judd-Ofelt intensity parameters of Er³⁺ have been determined to calculate the radiative transition probabilities and the radiative lifetimes of excited states. An infrared to visible up-conversion was observed at room temperature in this tellurite glass system using a 797 nm excitation line. A study of the ⁴S_3/2-⁴I_15/2 transition (554 nm) versus power excitation provided evidence for a two-step up-conversion process under this excitation. A red emission (663 nm) originating from the ⁴F_9/2-⁴I_15/2 transition has been observed as well. It was found that the efficiency of this up-conversion line is enhanced considerably with the Er³⁺ concentration relative to the green emission (554 nm). This behaviour has been explained in terms of an energy transfer between excited ions. The temperature dependence of up-conversion intensity has been also studied in the range 40-310 K. It was found that the thermal quenching of the green emission (⁴S_3/2-⁴I_15/2) is large enough compared with those of the red transition (⁴F_9/2-⁴I_15/2 ). This thermal quenching has been discussed using the Riseberg and Moos model of multiphonon emission. It has been shown that the latter approach is not consistent with existing results. A complete analysis of the temperature-dependent up-conversion has been made using an additional decay rate which may be attributed to a non-radiative energy transfer and/or a charge transfer through trapping impurities. A good agreement has been achieved between measured and computed data.