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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.

We present a theoretical study of the subband structure of both single and periodically δ-doped GaAs layers. We will discuss the influence of the δ-doping concentration and the δ-layer spacing on the confinement properties of such structures. A self-consistent analysis is made on these δ-doping systems in two different cases: (i) in the presence of a uniform electric field and inside an infinite potential barrier and (ii) under a linearly varying built-in electric field and within a finite potential barrier. Two features have been observed for the Stark effect in the first case: (i) when the electric field increases, the energies of the electronic subbands become lower and simultaneously a second quantum well appears and (ii) for larger electric fields, the subband structure is dramatically changed and the main role of confining charge carriers is reversed to the new quantum well. In the second case, the Stark effect is studied by taking, as a finite barrier, the Schottky potential of a δ-GaAs diode. One main effect was observed: the distortion of the V-shaped potential being more or less accentuated, depending on the applied bias voltage being reverse or direct respectively. Photocurrent (PC) data of a Si δ-doped GaAs structure have been taken as experimental support to validate our computation.

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