Sidney Alves Lourenço

Comparison of some theoretical models for fittings of the temperature dependence of the fundamental energy gap in GaAs

In this work we report on a comparison of some theoretical models usually used to fit the dependence on temperature of the fundamental energy gap of semiconductor materials. We used in our investigations the theoretical models of Vi˜ na, P¨ assler-p and P¨ assler-r to fit several sets of experimental data, available in the literature for the energy gap of GaAs in the temperature range from 12 to 974 K. Performing several fittings for different values of the upper limit of the analyzed temperature range (T max), we were able to follow in a systematic way the evolution of the fitting parameters up to the limit of high temperatures and make a comparison between the zero-point values obtained from the different models by extrapolating the linear dependence of the gaps at high T to T = 0 K and that determined by the dependence of the gap on isotope mass. Using experimental data measured by absorption spectroscopy, we observed the non-linear behavior of Eg(T) of GaAs for T > QD.

Optical properties of Cr-doped Zn1−xMnxTe semimagnetic nanocrystals

The effect of Cr co-doping on the optical properties of Mn-doped ZnTe nanocrystals (NCs) embedded in a glass matrix is studied in this paper. The substitutional incorporation of Cr2+ ions into these semiconducting NCs was strongly evidenced by optical absorption and crystal field theory analyses, which showed the characteristic transitions of Cr2+ and Cr3+ ions. Transmission electron microscopy images revealed the NC size and invariance lattice parameter, with the incorporation of Mn2+ and Cr2+ ions. PL spectra showed that co-doping with Cr favors a competition between Mn2+ and Cr2+ ions, resulting in a decrease in the rate of Mn2+ substitution, zinc vacancy filling (VZn) in Zn1−x−yMnxCryTe NCs, and the formation of interstitial Cr3+ ions in the host glass system.

Optical Properties of Semiconductor Nanocrystals into the Glass and Colloidal Environments for New Technological Applications

Semiconductor quantum dots (QDs) became in the last decade an important class of materials by present continuous tunability of electronic and optical properties by changing size and shape [1–4]. These new physical properties presented by QDs have demonstrated potential applications in different technologic areas as light-emitting devices [5–8], low-threshold lasers [9], optical amplifiers [10], photovoltaic devices [11–14], biological labels [15, 16], antibacterial control [17], and cancer therapy [18]. In the visible and violet spectral range, CdS- and CdSe-based QDs become a prototypical among QDs, for above applications, due to highly reproducible and controllable emission from violet to red. The ability to synthesize stable QDs via colloidal aqueous solutions is extremely important for same application areas. For medical and biotechnological applications, for example, water-soluble QDs are needed [19, 20], and appropriate functionalizations will define its specific applications [21–23]. Thus, surface passivation and functionalization of QD systems are important methods that can improve their well-defined physical and chemical properties [24, 25]. Although QDs or QDs doped with impurities (metal or magnetic) are currently being synthesized by colloidal chemistry techniques [26, 27] or molecular beam epitaxy (MBE) [28], some possible applications of interest, technological, in particular, require nanoparticles to be embedded in robust and transparent host materials. In this context, the melting-nucleation approach appears as an appropriate synthesis technique since it allows the growth of diluted magnetic semiconductor NCs embedded in different glass matrices, which can avoid undesirable effects on the nanostructures, such as corrosion and humidity [29–31].