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ZnO:Al thin films doped with different aluminum concentrations were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature using, for the first time, nanocrystalline powder synthesized by the sol–gel method. The aluminum doping concentration was varied from 2.0 to 4.5 at.%. All the films exhibited an intensive (002) XRD peak, indicating that they have c-axis-preferred orientation. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the morphology of the films. They have a typical columnar structure and a very smooth surface. The optical transmittance spectra showed a good transmittance higher than 90% within the visible region. The best conductors, with an optical band gap of 3.46 eV and a minimum resistivity of 5.4 × 10−4 Ω cm, were obtained for ZnO:Al films containing 3.0 at.% of aluminum. Due to their good optical and electrical properties, ZnO:Al films are promising candidates for use as transparent electrodes in solar cells.

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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