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 4S3/2-4I15/2 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 4F9/2-4I15/2 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 (4S3/2-4I15/2) is large enough compared with those of the red transition (4F9/2-4I15/2 ). 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.

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Subject classification: 78.55.Hx; S10.1 Photoluminescence properties of Er 3+ -doped 70TeO 2 -30ZnO glasses are investigated. Infrared to visible upconversion has been observed at room temperature in this tellurite glass using a 797 nm excitation laser. A study of the 4 S 3/2 ! 4 I 15/2 and 4 F 9/2 ! 4 I 15/2 transitions versus excitation laser power shows evidence for a two-step upconversion process under this excitation. The red emission originating from the 4 F 9/2 ! 4 I 15/2 transition is enhanced relative to the green emission with increasing Er 3+ ion concentration. This behaviour has been explained as being due to an energy transfer between activator ions. The temperature dependence of the upconversion intensity has also been studied in the range 60-310 K. It was found that the red emission of 4 F 9/2 ! 4 I 15/2 grows considerably relative to the green transition with increasing temperature in heavily doped samples. This indicates that energy transfer mechanisms, responsible for the red emission enhancement, are temperature dependent.

We report time-resolved luminescence data for the 4 F 3/2 → 4 I 11/2 transition in Nd 3+doped zinc tellurite glass. The photoluminescence (PL) shows nonexponential decay and the associated decay time depends on ion concentration. PL results are analysed and discussed using the stretched exponential function, commonly used to describe disordered systems. The nonexponential behaviour has been explained as due to a multi-configurational distribution of luminescent ions in a disordered medium. The dipole-dipole interactions remain at the origin of the PL decay time shortening.

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