Reconstruction of deformed defects in field theory from deformed zero modes and applications

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structural and spectroscopic study of oxyfluoride glasses and glass-ceramics using europium ion as a structural probe

Transparent oxyfluoride glasses and beta-PbF(2) nanocrystals containing glass-ceramics were prepared with varying Eu(3+) content (0.3, 0.4, 0.5 and 0.6%). The effect of Eu(3+) content on the preparation of glass-ceramics was investigated. From differential scanning calorimetry, the T(x)-T(g)(T(x)-temperature of the onset of crystallization; T(g)-glass transition temperature) parameter for glasses has shown slight variation, and an exothermic peak near T(g) called the ceramization temperature (T(c)) has been observed. Heat treatments were performed at this temperature to obtain transparent glass-ceramics containing beta-PbF(2) nanocrystals, identified by x-ray diffraction. Heat treatments for different periods of time were performed and were observed to be very important in the control of the crystal size and of the crystallization rate. Based upon the absorption spectra, the scattering level due to the presence of beta-PbF(2) nanocrystals in the glass-ceramics was observed to be similar to that for the mother glasses. Detailed analysis of emission spectra and decay time measurements led to the identification of Eu(3+) ions as the beta-PbF(2) crystalline phase. Excitation spectra at 70 K show the interaction of Eu(3+) ions with the fluorogermanate network.

Synthesis and Photoluminescence Behavior of the Eu3+ Ions as a Nanocoating over a Silica Stober Matrix

In this work, a SiO2 spherical were prepared by the Stober Method and then recovered with a single layer of Eu2O3 oxide (SiO2@Eu2O3) obtained by the Polymeric Precursor Method. The SiO2@Eu2O3 powder was heated treated at 100, 300, 400, 500 and 800 A degrees C. The samples were characterized by the Scanning Electonic Microscopy (SEM), Thermal Analysis (TGA/DTA), and the luminescent properties of the SiO2@Eu2O3 powders were studied by their emission and excitation spectra as well as by the lifetime measurements of the Eu3+ D-5(0) -> aEuro parts per thousand F-7(2) transition. The SEM analysis shows that the silica prepared by the Stober Method is spherical with a particle size of 460 nm. The emission spectra of the SiO2@Eu2O3 powders presented the Eu3+ characteristics bands related to the D-5(0) -> aEuro parts per thousand F-7(J) (J = 0, 1, 2, 3, 4) transitions at 577, 591, 616, 649 and 695 nm, respectively. The band related to the D-5(0) -> aEuro parts per thousand F-7(2) transition is the most intense in the spectra, and its intensity decreases with the temperature enhancement. The decay curves of the SiO2@Eu2O3 samples presented monoexponential features, and the obtained lifetime values were higher than the Eu2O3 oxide. It was possible to conclude that the D-5(0) -> aEuro parts per thousand F-7(2) hypersensitive transition is strongly dependent on the Eu3+ surrounding.

BaMoO4:Tb3+ phosphor properties: Synthesis, characterization and photophysical studies

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Spectroscopic study of lanthanide squarate hydrates

In the present investigation some spectroscopic properties of several lanthanide squarate hydrates are reported. The Raman spectra show the same distinctive Jahn-Teller intensity pattern for non-totally symmetric modes, as previously observed for the free anion. In the case of the terbium salt, the Tb3+ emission is very intense even at room temperature, revealing an efficient excitation via the ligand electronic levels. The Tb3+ dilution in Gd3+ or La3+ hosts increases this excitation efficiency without any appreciable variation in the 5D4 excited-state lifetime. However, the Eu3+ emission is very weak, with excited states located above the 5D2 level (ca. 21 550 cm-1) being completely quenched at room temperature. At lower temperatures higher-lying levels are not so efficiently quenched. The broad band observed in the UV excitation spectra of Eu3+ and Tb3+ is easily assigned to an intra-ligand transition leading to ligand-to-lanthanide ion energy transfer processes. As observed for Tb3+, Eu3+ dilution in Gd3+ or La3+ hosts also increases the relative emission intensity mediated by the ligand, without variation in the 5D0 excited-state lifetime. The Eu3+ 5D0 excitation spectra show vibronic structures that can be interpreted on the basis of the data available from the vibrational spectra. An increase in the vibronic intensities is observed as the lanthanide concentration is increased. © 1994.

Visible to infrared energy conversion in Pr3+-Yb3+ co-doped fluoroindate glasses

Processes involving visible to infrared energy conversion are presented for Pr3+-Yb3+ co-doped fluoroindate glasses. The emission in the visible and infrared regions, the luminescence decay time of the Pr 3+:3P0 → 3H4 (482 nm), Pr3+:1D2 → 3H6 (800 nm), Yb3+:2F5/2 → 2F 7/2 (1044 nm) transitions and the photoluminescence excitation spectra were measured in Pr3+ samples and in Pr3+-Yb 3+ samples as a function of the Yb3+ concentration. In addition, energy transfer efficiencies were estimated from Pr3+: 3P0 and Pr3+:1D2 levels to Yb3+:2F7/2 level. Down-Conversion (DC) emission is observed due to a combination of two different processes: 1-a one-step cross relaxation (Pr3+:3P0 → 1G4; Yb3+:2F7/2 → 2F5/2) resulting in one photon emitted by Pr3+ (1G4 → 3H5) and one photon emitted by Yb3+ (2F7/2 → 2F5/2); 2-a resonant two-step first order energy transfer, where the first part of energy is transferred to Yb3+ neighbor through cross relaxation (Pr3+:3P0 → 1G4; Yb3+:2F7/2 → 2F5/2) followed by a second energy transfer step (Pr 3+:1G4 → 3H4; Yb3+:2F7/2 → 2F5/2). A third process leading to one IR photon emission to each visible photon absorbed involves cross relaxation energy transfer (Pr3+: 1D2 → 3F4; Yb 3+:2F7/2 → 2F5/2). © 2013 Elsevier B.V. All rights reserved.

Interação do complexo luminescente [Eu(tta)3] com sílica mesoporosa

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Férmions em campos externos em 1+1 e 2+1 dimensões

Pós-graduação em Física - FEG

Propriedades fotoluminescentes de complexos tetrakis (β-dicetonatos) de európio para aplicação como dispositivos conversores de luz

Pós-graduação em Química - IBILCE

Preparação e caracterização de coacervatos e vidros a base de fosfato, dopados com európio

Pós-graduação em Química - IQ

Spherical-shaped Y2O3:Eu3+ nanoparticles with intense photoluminescence emission

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Viabilidade do Código MCNPX para o Estudo da Técnica de Fluorescência de Raios-X por Reflexão Total

The X-ray fluorescence analysis (XRF) is an important technique for the qualitative and quantitative determination of chemical components in a sample. It is based on measurement of the intensity of the emitted characteristic radiation by the elements of the sample, after being properly excited. One of the modalities of this technique is the total reflection x-ray fluorescence (TXRF). In TXRF, the angle of refraction of the incident beam tends to zero and the refracted beam is tangent to the sample-support interface. Thus, there is a minimum angle of incidence that there is no refracted beam and all the incident radiation undergoes total reflection. As it is implemented in very small samples, in a film format, self-absorption effects should not very relevant. In this study, we evaluated the feasibility of using code MCNPX (Monte Carlo N - Particle eXtended), to simulate a measure implemented by the TXRF technique. In this way, it was verified the quality of response of a system by TXRF spectroscopy using synchrotron radiation as excitation beam for a simple setup, by retrieving the characteristic energies and the concentrations of the elements in the sample. The steps of data processing, after obtaining the excitation spectra, were the same as in a real experiment and included the obtaining of the sensitivity curve for the simulated system. The agreement between the theoretical and simulated values of Ka characteristic energies for different elements was lower than 1 % .The obtained concentration of the elements of the sample had high relatively errors ( between 6 and 60 % ) due mainly to lack of knowing about some realistic physical parameters of the sample , such as density . In this way, this result does not preclude the use of MCNPX code for this type of application

Resonant excitation of Mn local vibrational modes in the higher order Raman spectra of nanocrystalline Ga(1-x)Mn(x)N films

The effect of manganese on the vibrational properties of Ga(1-x)Mn(x)N (0 <= x <= 0.18) films has been investigated by Raman scattering using 488.0 and 632.8 nm photon excitations. The first-order transverse and longitudinal optical GaN vibrational bands were observed in the whole composition range using both excitations, while the corresponding overtones, as well as a prominent peak located in 1238 cm(-1) (153.5 meV) were only observed in the Mn-containing films under 488.0 nm excitation. We propose that the peak observed at 1238 cm(-1) is due to resonant Mn local vibrational modes, the excitation process being related to electronic transitions involving the Mn acceptor band.

Efficiency of extrinsic and intrinsic charge-carrier photogeneration processes obtained from the steady-state photocurrent action spectra of poly(p-phenylene vinylene) derivatives

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Ultraviolet excitation of photoconductivity in thin films of sol-gel SnO2

Tin dioxide (SnO2) thin film photoconductivity spectra were measured for a large temperature range using a deuterium source, the intensity of photocurrent spectra in the range 200-400 nm is temperature dependent, and the photocurrent increases in the ultraviolet even for illumination with photon energies much higher than the bandgap transition. This behavior is related to recombination of photogenerated electron-hole pairs with oxygen adsorbed at grain boundaries, which is consistent with nanoscopic crystallite size of sol-gel deposited films. (c) 2005 Elsevier Ltd. All rights reserved.