Sol-gel preparation of near-infrared broadband emitting Er(3+)-doped SiO(2)-Ta(2)O(5) nanocomposite films

This article reports a study on the preparation, densification process, and structural and optical properties of SiO(2)-Ta(2)O(5) nanocomposite films obtained by the sol-gel process. The films were doped with Er(3+) and the Si:Ta molar ratio was 90:10. Values of refractive index, thickness and vibrational modes in terms of the number of layers and thermal annealing time are described for the films. The densification process is accompanied by OH group elimination, increase in the refractive index, and changes in film thickness. Full densification of the film is acquired after 90 min of annealing at 900 degrees C. The onset of crystallization and devitrification, with the growth of Ta(2)O(5) nanocrystals occurs with film densification, evidenced by high-resolution transmission electron microscopy. The Er(3+)-doped nanocomposite annealed at 900 degrees C consists of Ta(2)O(5) nanoparticles, with sizes around 2 nm, dispersed in the SiO(2) amorphous phase. The main emission peak of the film is detected at around 1532 nm, which can be assigned to the (4)I(13/2)->(4)I(15/2) transition of the Er(3+) ions present in the nanocomposites. This band has a full width at half medium of 64 nm, and the lifetime measured for the (4)I(13/2) levels is 5.4 ms, which is broader compared to those of other silicate systems. In conclusion, the films obtained in this work are excellent candidates for use as active planar waveguide. (C) 2010 Elsevier B.V. All rights reserved.

Magnetic and structural properties of NiFe(2)O(4) ferrite nanopowder doped with Zn(2+)

This work involved an investigation to ascertain how the substitution of nickel ions for zinc ions affects the structural, morphological and magnetic properties of NiFe(2)O(4) ferrite samples. Ni(1-x)Zn(x)Fe(2)O(4) (x = 0.0, 0.3 0.5, 0.7) powders were prepared by combustion reaction and characterized structurally by X-ray diffraction. The specific surface area of the powders was determined by the nitrogen adsorption method (BET). Magnetization measurements were taken using an alternative gradient magnetometer (AGM), which revealed that the powders prepared by combustion reaction resulted in nanosized particles with a particle size of 18-27 nm. The crystallite size and lattice parameter increased as the concentration of Zn increased. Moreover, augmenting the Zn content in the NiFe(2)O(4) ferrite increased the saturation magnetization and coercive field. (C) 2008 Elsevier B.V. All rights reserved.

Relaxation of the electrical resistivity in Cr-doped Nd(0.5)Ca(0.5)MnO(3) single crystals

We have performed a systematic study of the time and temperature dependencies of the electrical resistivity (rho(T, t)) inNd(0.5)Ca(0.5)Mn(1-x)Cr(x)O(3) single crystals with x = 0.02 and 0.07 in order to examine the dynamics of the phase separation. The relaxation effects can be described by the combination of a rapid exponential increase/decrease with a slower logarithmic contribution at longer times. The experimental results suggest the existence of a large temperature window in which huge relaxation effects occur, and the relative fraction of the coexisting phases rapidly changes as a function of time, depending on the initial magnetic state of the sample. The rho(T, t) relaxation measurements were shown to be a suitable tool for probing the dynamical nature of the phase separation, in which magnetically distinct phases compete against each other in a wide temperature range. In addition, the features observed in the rho(T, t) curves were found to be in excellent agreement with both the magnetic properties and the structural transitions observed in these manganites.

The effect of additional Si and SiGe layers on the confinement potential of GeMn diluted ferromagnetic semiconductor

In this work we analyze the spin-polarized charge density distribution in the GeMn diluted ferromagnetic semiconductors (DFS). The calculations are performed within a self-consistent k.p method, in which the exchange correlation effects in the local density approximation, as well as the strain effects due to the lattice mismatch, are taken into account. Our findings show that the extra confinement potential provided by the barriers and the variation of the Mn content in the DFS are responsible for a separation between the different spin charge densities, giving rise to higher mobility spin-polarized currents or high ferromagnetism transition temperatures systems. (c) 2008 Elsevier B.V. All rights reserved.

Evidence for magnetic phase separation in La(0.86)Sr(0.14)Mn(1-x)Cu(x)O(3+delta) manganites from NMR and magnetic measurements

Polycrystalline La(0.86)Sr(0.14)Mn(1-x)Cu(x)O(3+delta) (x = 0, 0.05, 0.10, 0.15, 0.20) manganites were investigated by means of magnetic measurements and zero-field (139)La and (55)Mn nuclear magnetic resonance (NMR) spectroscopy. Magnetization versus temperature measurements revealed a paramagnetic to ferromagnetic transition in most samples, with lower Curie temperatures and broader transitions for samples with higher Cu contents. The details of the magnetization measurements suggested a phase-separated scenario, with ferromagnetic clusters embedded in an antiferromagnetic matrix, especially for the samples with large Cu contents (x = 0.15 and 0.20). Zero-field (139)La NMR measurements confirmed this finding, since the spectral features remained almost unchanged for all Cu-doped samples, whereas the bulk magnetization was drastically reduced with increasing Cu content. (55)Mn NMR spectra were again typical of ferromagnetic regions, with a broadening of the resonance line caused by the disorder introduced by the Cu doping. The results indicate a coexistence of different magnetic phases in the manganites studied, with the addition of Cu contributing to the weakening of the double-exchange interaction in most parts of the material.

Fano resonance in heavily doped porous silicon

Unexpectedly, the Fano resonance caused by the interference of continuum electron excitations with the longitudinal optical (LO) phonons was observed in random porous Si by Raman scattering. The analysis of the experimental data shows that the electron states trapped at the Si-SiO(2) interface dominate in the observed Raman scattering. The gap energy associated with the interface states was determined. Copyright (C) 2011 John Wiley & Sons, Ltd.

Photocatalytic decomposition of methylene blue via Fenton mechanisms by silicon wafer doped with Au and Cu: a theoretical and experimental study

In this work, we studied the photocatalytic and the structural aspects of silicon wafers doped with Au and Cu submitted to thermal treatment. The materials were obtained by deposition of metals on Si using the sputtering method followed by fast heating method. The photocatalyst materials were characterized by synchrotron-grazing incidence X-ray fluorescence, ultraviolet-visible spectroscopy, X-ray diffraction, and assays of H(2)O(2) degradation. The doping process decreases the optical band gap of materials and the doping with Au causes structural changes. The best photocatalytic activity was found for thermally treated material doped with Au. Theoretical calculations at density functional theory level are in agreement with the experimental data.

Cation size effects-modified phase and PTCR development in Er3+ and Ca2+ co-doped BaTiO3 ceramics during sintering

Development of the positive temperature coefficient of resistivity (PTCR) in Er3+ and Ca2+ co-doped ferroelectric BaTiO3 was studied in this work, with Er3+ being used to act as a donor doping. Irrespective of all the materials showing high densities after sintering at 1200 to 1300 ºC, these revealed insulator at the lowest sintering temperature, changing to semiconducting and PTCR-type materials only when the sintering temperature was further increased. Observations from X-ray diffraction help correlating this effect with phase development in this formulated (Ba,Ca,Er)TiO3 system, considering the formation of initially two separated major (Ba,Ca)TiO3- and minor (Ca,Er)TiO3-based compounds, as a consequence of cation size-induced stress energy effects. Thus, appearance and enhancement here of the semiconducting and PTCR responses towards higher sintering temperatures particularly involve the incorporation of Er3+ into the major phase, rendering finally possible the generation and "percolative-like" migration of electrons throughout the whole material.

Enhanced response of the fricke solution doped with hematoporphyrin under X-rays irradiation

The vials filled with Fricke solutions were doped with increasing concentrations of Photogem®, used in photodynamic therapy. These vials were then irradiated with low-energy X-rays with doses ranging from 5 to 20 Gy. The conventional Fricke solution was also irradiated with the same doses. The concentration of ferric ions for the Fricke and doped-Fricke irradiated solutions were measured in a spectrophotometer at 220 to 340 nm. The results showed that there was an enhancement in the response of the doped-Fricke solution, which was proportional to the concentration of the photosensitizer. The use of such procedure for studying the radiosensitizing property of photosensitizers based on the production of free radicals is also discussed.

Preparação de membranas de acetato de celulose organomodificadas para adsorção dos íons Cu(II), Cd(II), Mn(II) e Ni(II)

Cellulose acetate polymeric membranes had been prepared by a procedure of two steps, combining the method of phase inversion and the technique of hydrolysis-deposition. The first step was the preparation of the membrane, and together was organomodified with tetraethylortosilicate and 3-aminopropyltrietoxysilane. Parameters that exert influence in the complexation of the metallic ion, as pH, time of complexation, metal concentration, had been studied in laboratory using tests of metal removal. The membranes had presented resistance mechanics and reactivity to cations, being able to be an alternative for the removal, daily pay-concentration or in the study of the lability of metals complexed.

Utilização de pelos de animais silvestres para monitoramento ambiental de Cd, Cr, Cu, Fe, Mn, Pb e Zn

This study investigates the use of wild animal hair of C. brachyurus, C. thous and L. pardalis as biomonitors of trace metal at Parque Nacional das Emas, Brazil. Results reveal a strong correlation between Cd and Pb as well as Cu and Zn, which suggests a single source of emission. Most metals showed a lower or equal concentration than those obtained in previous studies. The research shows that monitoring may be performed only with Zn, Pb, Cd, and Cr because of statistical similarity and of a non-natural occurrence of large amounts of the material under analysis.

Evaluation of Ti(3)Si Phase Stability from Heat-Treated, Rapidly Solidified Ti-Si Alloys

Ti-base alloys containing significant amounts of silicon have been considered for high temperature structural applications. Thus, information concerning phase stability on the Ti-Si system is fundamental and there are not many investigations covering the phase stability of the Ti(3)Si phase, specially its dependence on oxygen/nitrogen contamination. In this work the stability of this phase has been evaluated through heat-treatment of rapidly solidified Ti-rich Ti-Si alloys at 700 A degrees C and 1000 A degrees C. The rapidly solidified splats presented nanometric scale microstructures which facilitated the attainment of equilibrium conditions. The destabilization of Ti(3)Si due to oxygen/nitrogen contamination has been noted.

Microstructural Evidence of beta Co(2)Si- phase Stability in the Co-Si System

The aim of this work was to verify the stability of the beta Co(2)Si phase in the Co-Si system. The samples were produced via arc-melting and characterized through Scanning Electron Microscopy (SEM) and Differential Thermal Analysis (DTA). The results have confirmed the stability of the beta Co(2)Si phase, however, a modification of the shape of beta CoSi phase field is proposed in order to fully explain the results.

Applications of the Rietveld method to quantify the crystalline phases of Portland cement clinker doped with nickel and chromium

The effects of chromium or nickel oxide additions on the composition of Portland clinker were investigated by X-ray powder diffraction associated with pattern analysis by the Rietveld method. The co-processing of industrial waste in Portland cement plants is an alternative solution to the problem of final disposal of hazardous waste. Industrial waste containing chromium or nickel is hazardous and is difficult to dispose of. It was observed that in concentrations up to 1% in mass, the chromium or nickel oxide additions do not cause significant alterations in Portland clinker composition. (C) 2008 International Centre for Diffraction Data.

Influence of metallic nanoparticles on electric-dipole and magnetic-dipole transitions of Eu(3+) doped germanate glasses

Luminescence properties of Eu(3+) doped germanate glasses containing either silver or gold nanoparticles (NPs) were investigated for excitation at 405 nm. Enhanced emissions and luminescence quenching of the Eu(3+) transitions in the range from 570 to 720 nm were observed for samples having various concentrations of metallic NPs. Electric-dipole and magnetic-dipole transitions that originate from the Eu(3+) level (5)D(0) exhibit large enhancement due to the presence of the metallic NPs. The results suggest that the magnetic response of rare-earth doped metal-dielectric composites at optical frequencies can be as strong as their electric response due to the confinement of the optical magnetic field. (C) 2010 American Institute of Physics. [doi:10.1063/1.3431347]