Caracterização optica de pontos quanticos de CdTe em matriz vitrea




Quanturn confinement effects in semiconductor nanoerystais have attracted a significant amount of interest in the last few years, because of their new optical properties and aiso because of their potential for optical device applications. ln this thesis the size-dependent optical properties of nanometer-scale semiconductor crystallites (or quantum dots) in doped glasses are investigated. We discuss the confinement effects of these nanocrystais under absorption, photoluminescence and photoluminescence exeitation (PLE) spectroscopies, as afunction of the sample temperature. The specimens studied are Cadmium Teiluride (CdTe) quantum dots grown by processes of heat treatment. The experimental results for the optical absorption spectra are compared with the calculated ones considering the transition energies from a spherical k-p model. The inhomogeneous broadening due to the quantum dot size distribution and the homogeneous broadening due mainiy to electron-phonon interactions have also been considerei. The results for the comparison show that the homogeneous width increases as the quantum dot size decreases. That means that the electron-phonon interaction increases for smail quantum dots. The standard deviation for the size-distribution is 5,8 % aecording to this anaiysis. The photoluminescence excitation measurements were compared to the absorption spectra and aiso analyzed through the same ko-p model. For the PLE, the comparison with theoretical predictions is not that efficient to explain the experimental data. Comparing the PLE and the absorption to the photoluminescence results, a Stokes-like shift is observed and aiso anaiyzed. Transmission electron microscopy (TEM), and far-field and near-field optical microscopies are used to extract "single dot" information. The direct size distribution measurement indicares a larger standard deviation than the value obtained from the optical absorption spectra. The optical microscopies allow us to study some other effects as the photodarkening and the photoblinking for these samples


microscopia eletronica analise espectral semicondutores - propriedades oticas

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