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Item type:Publication, Crystalline environment of luminescent Tb3+ ions embedded in indium tin oxide thin films: A DFT and crystal field analysis assessment(American Physical Society, 2025)We assess the local symmetry and crystal environment of trivalent terbium ions embedded in an indium tin oxide matrix with bixbyite structure. The Tb3+ ions tend to substitute In3+ ions in two different cationic sites (𝑏 and 𝑑). Density functional theory calculations suggest that the Tb3+ ions are mainly located at 𝐶2 symmetry sites, relaxing selection rules and enabling electric dipole transitions, with the 5 𝐷 4 → 7 𝐹 2 transition being the most intense, providing a red color to the light emission. Photoluminescence emission spectrum under UV excitation at 83 K revealed 30 intra-4𝑓 transitions, which were assigned to the 7 𝐹 𝐽 ground multiplet of the Tb3+ ion. Crystal field analysis shows a strong alignment between calculated and observed energy levels, yielding a standard deviation of 𝜎=15.1cm−1. We believe these results can help to understand the activation mechanisms of Tb3+ luminescent centers in transparent conductive oxides, as well as the potential to modulate Tb3+ emission color through its crystalline environment.2 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Revisiting the optoelectronic properties of sputtered aluminium-doped zinc oxide: a study combining advanced optical dispersion models(Institute of Physics, 2025)Aluminium-doped zinc oxide (AZO) thin films with different aluminium (Al) concentrations were grown by RF-magnetron sputtering with substrate active cooling. Sputtering induced sample heating was aimed to be mitigated by the applied cooling, achieving films with electrical resistivities as low as 3.3 × 10 − 3 Ω ⋅ cm , in the as-deposited state. Subsequently, an annealing treatment was performed to enhance the electrical properties and assess the effect of the Al concentration. The absorption coefficient spectra of zinc oxide (ZnO) exhibits an excitonic absorption contribution to the fundamental absorption that is typically not considered in AZO when determining the optical bandgap. Nevertheless, here we show that this free exciton band remains visible in AZO even at Al concentrations greater than 4 at.%. Additionally, the doping-induced defect states increases the width of tail states. These two factors have a substantial effect on the absorption edge, and thus must be considered with adequate models when attempting to determine the optical bandgap. In this work, we use a recently developed Elliot-based optical dispersion model to accurately determine the optical bandgap, exciton binding energy and Urbach energy of AZO thin films. On the other hand, we assess the infrared free carrier absorption, typically modeled by the Drude dispersion formula, by considering a complex frequency-dependent dynamical resistivity and the polar nature of the ZnO lattice. Normally, the real part of the dynamical resistivity follows a power law dependence and the exponent is assumed to be −1.5 for highly-doped semiconductors. Notwithstanding, here we let this exponent as a free fitting parameter to assess the effect of distinct scattering mechanisms present in sputtered AZO thin films and its dependence with the Al doping concentration. We believe these results can be extended to other degenerated semiconductors and are relevant for the understanding and tailoring of their fundamental optoelectronic properties.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Description of excitonic absorption using the Sommerfeld enhancement factor and band-fluctuations(Institute of Physics, 2025)One of the challenges of excitonic materials is the accurate determination of the exciton binding energy and bandgap from optical measurements. The difficulty arises from the overlap of the discrete and continuous excitonic absorption at the band edge. Many researches have modeled the shape of the absorption edge of such materials on the seminal formulation proposed by Elliott in 1957 ( Phys. Rev. 108 1384–9) and its several modifications such as non-parabolic bands, magnetic potentials and electron–hole-polaron interactions. However, exciton binding energies obtained from optical absorption often vary strongly depending on the chosen ‘Elliott formula’. Here, we propose an alternative and rather simple approach, which has previously been successful in the determination of the optical bandgap of amorphous, direct and indirect semiconductors, based on the band-fluctuations (BFs) model. In this model, the fluctuations due to disorder, temperature or lattice vibrations give rise to the well known exponential shape of band tail states. The formulation results in an analytic equation for the fundamental absorption with 6 parameters only. To test it, the binding energy and optical bandgap of GaAs and the family of tri-halide perovskites ( MAPbX 3 ), X = Br , I , Cl , over a wide range of temperatures, are obtained by fitting the modified Elliott model. The results for the bandgap, linewidth and exciton binding energy are in good agreement with reports based on non-optical measurements. Moreover, due to the polar nature of perovskites, the retrieved binding energies can be compared with those computed with a model proposed by Kane (1978 Phys. Rev. B 18 6849). In the latter model, the exciton is surrounded by a cloud of virtual phonons interacting via the Frölich interaction. As a consequence, the upper bound for the binding energy of the exciton-polaron system can be estimated. These results are in good agreement with the optical parameters obtained with the proposed Elliott equation including BFs.1