N.O. Dantas

Evidence of Cd1−xMnxS nanocrystal growth in a glass matrix by the fusion method

In this work, CdS nanocrystals (NCs) doped with Mn were synthesized in a glass matrix by fusion. The as-grown Cd1−xMnxS NCs were investigated by optical absorption, atomic force microscopy, and electron paramagnetic resonance (EPR). The incorporation of Mn2+ ions in CdS NCs was confirmed by an absorption transition blueshift with increasing Mn concentration x. EPR spectra demonstrated the existence of two distinct Mn2+ ion locations: one incorporated in the core and the other near the surface of the Cd1−xMnxS NCs. The hyperfine interaction constants used to simulate the EPR spectra were A=7.6 and 8.2 mT, respectively. The synthesis of high quality Cd1−xMnxS NCs may allow the control of optical and magnetic properties.

Effect of Fe2O3 concentration on the structure of the SiO2-Na2O-Al2O3-B2O3 glass system.

The structural properties of the glass matrix 40SiO(2)·30Na(2)O·1Al(2)O(3)·(29-x)B(2)O(3)·xFe(2)O(3) (mol%), 0.0≤x≤29.0 were studied by X-ray diffraction (XRD), differential thermal analysis (DTA) and Raman and infrared spectroscopy (FT-IR). XRD demonstrated Fe(3)O(4) crystal formation for Fe(2)O(3) concentrations of 29.0 mol%. DTA showed that glass transition and crystallization temperatures changed as a function of Fe(2)O(3) concentration and that these alterations were related to structural change in the glass system. Interesting aspects of Raman and FT-IR spectra were found, and this gives information about of the structure changes in Si-O-Si units of these glasses as a function of Fe(2)O(3) concentration.

Characterization and properties of CdO nanocrystals incorporated in polyacrylamide

CdO quantum dots (QDs) incorporated in polyacrylamide were synthesized adding aqueous suspension of cadmium oxide in acrylamide:bisacrylamide copolymer. Optical properties of CdO nanocrystals were studied by optical absorption. The size ranges (2-3 nm) were calculated by the effective mass approximation.

Shell Thickness Modulation in Ultrasmall CdSe/CdSxSe1–x/CdS Core/Shell Quantum Dots via 1-Thioglycerol

In this study, we report on the synthesis of CdSe/CdS core-shell ultrasmall quantum dots (CS-USQDs) using an aqueous-based wet chemistry protocol. The proposed chemical route uses increasing concentration of 1-thioglycerol to grow the CdS shell on top of the as-precipitated CdSe core in a controllable way. We found that lower concentration of 1-thioglycerol (3 mmol) added into the reaction medium limits the growth of the CdSe core, and higher and increasing concentration (5-11 mmol) of 1-thioglycerol promotes the growth of CdS shell on top of the CdSe core in a very controllable way, with an increase from 0.50 to 1.25 nm in shell thickness. The growth of CS-USQDs of CdSe/CdS was confirmed by using different experimental techniques, such as optical absorption (OA) spectroscopy, fluorescence spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Data collected from OA were used to obtain the average values of the CdSe core diameter, whereas Raman data were used to assess the average values of the CdSe core diameter and CdS shell thicknesses.

Control of luminescence emitted by Cd1 − xMnxS nanocrystals in a glass matrix: x concentration and thermal annealing

Cd(1-x)Mn(x)S nanocrystals (NCs) were successfully grown in a glass matrix and investigated by photoluminescence (PL), electron paramagnetic resonance (EPR) and magnetic force microscopy (MFM). We verified that the luminescent properties of these NCs can be controlled both by changing the x concentration and by thermal annealing of the samples. The EPR and PL data showed that the characteristic emission of Mn(2+) ions ((4)T(1)-(6)A(1)) is only observed when this magnetic impurity is substitutionally incorporated in the Cd(1-x)Mn(x)S NC core (site S(I)). Besides, it was observed that the emission ((4)T(1)-(6)A(1)) suppression, caused by the Mn(2+) ion presence near the surface (site S(II)) of the Cd(1-x)Mn(x)S NCs, is independent of the host material. The MFM images also confirmed the high quality of the Cd(1 - x)Mn(x)S NC samples, showing a uniform distribution of total magnetic moments in the nanoparticles.

Morphology in semimagnetic Pb1−xMnxSe nanocrystals: Thermal annealing effects

Samples of Pb1−xMnxSe nanocrystals were synthesized by fusion method and characterized by optical absorption, atomic force microscopy, x-ray diffraction, and electron paramagnetic resonance (EPR) techniques. Effects of Mn2+ ion incorporation into PbSe nanocrystals are manifested by well resolved optical spectra for different concentrations of Mn. The EPR spectra of as grown and thermal annealed Pb1−xMnxSe samples show that the magnetic properties of these Mn-doped nanocrystals can be tuned by thermal processes using different annealing times.

Magneto-optical properties of Cd1−xMnxS nanoparticles: influences of magnetic doping, Mn2+ ions localization, and quantum confinement

Cd(1-x)Mn(x)S nanoparticles (NPs) were successfully grown in a glass matrix and investigated by optical absorption (OA), magnetic circularly polarized photoluminescence (MCPL) measurements, and magnetic force microscopy (MFM). The room temperature OA spectra have revealed the formation of two groups of Cd(1-x)Mn(x)S NPs with different sizes: bulk-like nanocrystals (NCs) and quantum dots (QDs). The MCPL spectra were recorded at 2.0 K with several magnetic fields up to 15 T, allowing a detailed comparison between the degrees of circular polarization of the two groups of NPs. The different behaviours of magneto-optical properties of bulk-like NCs and QDs were explained by taking into account a considerable alteration of exchange interaction between the carrier spins and the substitutional doping magnetic ions incorporated into the NPs. As a main result, we have demonstrated that self-purification is the dominant mechanism that controls the doping in semiconductor QDs grown by the melting-nucleation synthesis approach due to the relatively high temperature that was used in thermal annealing of samples.

Experimental study of absorption and luminescence properties of Er3+ in lead silicate glass

Abstract The optical absorption and temperature dependence of photoluminescence (PL) in the temperature range of 10 to 300 K have been measured for Er3+-doped lead silicate glass. A strong PL band that originates from 4S13/2→4I15/2 transition centered at 562 nm was observed even at room temperature. A very weak temperature quenching compared with that of Er3+ in crystal Si and the peak wavelength remaining constant with temperature are the main characteristics of this PL emission band. They are explained by the competition of thermal population effect and multiphonon relaxation between the 4S3/2 and 2H11/2 levels of Er3+.

Controlling the cytotoxicity of CdSe magic-sized quantum dots as a function of surface defect density.

Quantum dots are potentially very useful as fluorescent probes in biological systems. However, they are inherently cytotoxic because of their constituents. We controlled the cytotoxicity of CdSe magic-sized quantum dots (MSQDs) as a function of surface defect density by altering selenium (Se) concentration during synthesis. Higher Se concentrations reduced the cytotoxicity of the CdSe MSQDs and diminished mRNA expression of methallothionein because of the low cadmium ions (Cd(2+)) concentration adsorbed on the surface of the MSQDs. These results agree with luminescence spectra, which show that higher Se concentrations decrease the density of surface defects. Therefore, our results describe for the first time a simple way of controlling the cytotoxicity of CdSe MSQDs and making them safer to use as fluorescence probes in biological systems.

Energy transfer between CdS nanocrystals and neodymium ions embedded in vitreous substrates

Experimental evidence has been observed for energy transfer from CdS nanocrystals, synthesized by the fusion method, to Nd(3+) ions embedded in vitreous substrates. These dot samples doped with neodymium have been investigated by combined optical absorption (OA), photoluminescence (PL), and time-resolved photoluminescence (PLRT) techniques. Radiative and nonradiative energy transfers between CdS dot and Nd(3+) ion levels, to our knowledge not reported before, can be clearly observed in the PL spectra where the emission band valleys correspond exactly to the energy absorption peaks of the doping ion. The PLRT data reinforce these energy transfer mechanisms in which the increasing overlap between the CdS PL band and the OA to the Nd(3+) levels decreases stimulated emissions from the doping ions.