Estudo das Propriedades Ópticas, Morfológicas e Magnéticas de Pontos Quânticos de CdTe e Cd1-xMnxTe em Matriz Vítrea

Abstract

CdTe and Cd1-xMnxTe quantum dots (QDs) were successfully grown in the Glass System SiO2 - Na2CO3 - Al2O3 - B2O3, doped with CdTe and Mn precursors, when subjected to appropriate thermal annealing. SNAB Glass Matrix, both doped and not doped with CdTe and Cd1-xMnxT quantum dots precursors was synthesized by melting method. The glass transition temperature (Tg) of SNAB Glass Matrix was determined by Differential Thermal Analysis (DTA), in order to decide the temperature of thermal annealing at 555ºC that favored the kinetics growth of CdTe and Cd1-xMnxTe QDs. Formation and kinetics growth of CdTe and Cd1-xMnxTe quantum dots were investigated by Optical Absorption (OA), Photoluminescence (PL), Atomic Force Microscopy (AFM), Magnetic Force Microscopy (MFM) and Electron Paramagnetic Resonance (EPR). OA spectra of samples provided evidence that CdTe and Cd1-xMnxTe QDs were formed. Based on these spectra and using the effective mass approximation model, it was verified the average radius of quantum dots around 2.0 nm. It was observed that PL spectra of CdTe QDs by increasing time intervals of the thermal annealing helps the diffusion of vacancies (Cadmium vacancies) and decreases the defect level emissions (Cadmium vacancies). Increasing manganese concentration on samples with Cd1-xMnxTe QDs intensifies the characteristic emission of Mn2+ ions (4T1 → 6A1) besides inducing an increase in the density of shallow surface defect levels. However, the increase of manganese concentration induces a decrease of defect level emissions associated with vacancies. It was also observed that increasing time intervals of thermal annealing intensifies shallow surface defect levels emissions and decreases emissions from Mn2+ ions and defect level (Cadmium vacancies). From the EPR spectra it was possible to confirm the Mn2+ ions incorporated into the CdTe QDs, as well as the relative decrease of Mn2+ ions concentration by increasing time intervals of the thermal annealing. AFM/MFM images reinforced the CdTe and Cd1-xMnxTe QDs formation. It was concluded from the obtained results that CdTe and Cd1-xMnxTe QDs were formed in the Glass System SNAB, and confirmed that Mn2+ ions incorporated into CdTe QDs can be controlled by manganese concentration function and by time intervals of the thermal annealing.