Light emitting diodes containing Langmuir-Blodgett films of copolymer of a poly(p-phenylene-vinylene) derivative and poly(octaneoxide)

The properties of Langmuir and Langmuir-Blodgett (LB) films from a block copolymer with polyethylene oxide and phenylene-vinylene moieties are reported. The LB films were successfully transferred onto several types of substrates, with sufficient quality to allow for evaporation of a metallic electrode on top of the LB films to produce polymer light emitting diodes (PLEDs). The photoluminescence and electroluminescence spectra of the LB film and device were similar, featuring an emission at ca. 475 nm, from which we could infer that the emission mechanisms are essentially the same as in poly(p-phenylene) derivatives. Analogously to other PLEDs the current versus voltage characteristics of the LB-based device could be explained with the Arkhipov model according to which charge transport occurs among localized sites. The implications for nanotechnology of the level of control that may be achieved with LB devices will also be discussed.

Photoluminescence properties of PZT 52/48 synthesized by microwave hydrothermal method using PVA with template

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Contribution of structural order-disorder to the room-temperature photoluminescence of lead zirconate titanate powders

Intense and broad visible photoluminescent (PL) band was observed at room temperature in structurally disordered PbZr0.53Ti0.47O3 powders. The lead zirconate titanate PbZr0.53Ti0.47O3 powders prepared by the polymeric precursor method and heat treated at different temperatures were structurally characterized at long range by means of X-ray diffraction. The PL was measured at room temperature samples heat treated at different temperatures. Experimental measurements and quantum-mechanical calculations showed that the high structural order and the high structural disorder in PbZr0.53Ti0.47O3 lattice are not favorable to the intense PL emission. Only samples containing simultaneous structural order and disorder in their lattice present the intense visible PL emission at room temperature. (C) 2007 Published by Elsevier B.V.

Structural and spectroscopic characterization of Al2-xCrxO3 powders obtained by polymeric precursor method

Al2O3 and Al2-x Cr (x) O-3 (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL* a*b* color data). The obtained results allow to identify the gamma-Al2O3 to alpha-Al2O3 phase transition. The single-phase alpha-Al2O3 powder was obtained after heat treatment at 1050 degrees C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al2-x Cr (x) O-3 are related to the gamma to alpha-Al2O3 phase transition and the temperature and time range for such transition depends on the chromium content.

Study of structural evolution and photoluminescent properties at room temperature of Ca(Zr, Ti)O-3 powders

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Quantum Mechanics Insight into the Microwave Nucleation of SrTiO3 Nanospheres

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

SnO2 nanocrystals synthesized by microwave-assisted hydrothermal method: towards a relationship between structural and optical properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Synthesis, characterization and photophysical properties of Eu3+ doped in BaMoO4

In this work Ba0.99Eu0.01MoO4 (BEMO) powders were prepared by the first time by the Complex Polymerization Method. The structural and optical properties of the BEMO powders were characterized by Fourier Transform Infra-Red (FTIR), X-ray Diffraction (XRD), Raman Spectra, High-Resolution Scanning Electron Microscopy (HR-SEM) and Photoluminescent Measurements. XRD show a crystalline scheelite-type phase after the heat treatment at temperatures greater than 400 degrees C. The ionic radius of Eu3+ (0.109 nm) is lower than the Ba2+ (0.149 nm) one. This difference is responsible for the decrease in the lattice parameters of the BEMO compared to the pure BaMoO4 matrix. This little difference in the lattice parameters show that Eu3+ is expected to occupy the Ba2+ site at different temperatures, stayed the tetragonal (S-4) symmetry characteristic of scheelite-type crystalline structures of BaMoO4. The emission spectra of the samples, when excited at 394 nm, presented the D-5(1)-> F-7(0, 1 and 2) and D-5(0)-> F-7(0, 1, 2, 3 and 4) Eu3+ transitions at 523, 533, 554, 578, 589, 614, 652 and 699 nm, respectively. The emission spectra of the powders heat-treated at 800 and 900 degrees C showed a marked increase in its intensities compared to the materials heat-treated from 400 to 700 C. The decay times for the sample were evaluated and all of them presented the average value of 0.61 ms. Eu3+ luminescence decay time follows one exponential curve indicating the presence of only one type of Eu3+ symmetry site.

Aplicação e avanços da espectroscopia de luminescência em análises farmacêuticas

This paper provides a review on the latest advances and applications of the luminescence spectroscopy for the development of pharmaceuticals analyses methods, basically based on the photo- and chemiluminescence. The different forms of the drugs determination on pharmaceuticals through the fluorescence and chemiluminescence are discussed. The analyses include the drugs native fluorescence (liquid and solid-phases); the fluorescence from the oxidizing or reducing forms of the drug; the fluorescence from the chemical derivatization and their photochemistry and hydrolysis reactions. The quenching of luminescence and chemiluminescence generation for the pharmaceutical quantification are also shown. Finally, the trends and future perspectives of the luminescence spectroscopy in the field of the pharmaceutical research are discussed.

Estudo da decomposição térmica de oxalato de estrôncio dopado com cério(III) como precursor de materiais luminescentes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Filmes de titânio-silício preparados por spin e dip-coating

The conditions for the preparation of luminescent materials, consisting of Eu3+ ions entrapped in a titanium matrix, in the forma of a thin film, using the sol-gel process, are described. The films were obtained from sols prepared with TEOS and TEOT, in the presence of acetylacetone as the hidrolysis-retarding agent, using the dip-coating and spin-coating techniques. The influence of these techniques on the films based on titanium and silicon are presented. The Eu3+ was used as a luminescent probe. The films have been characterized by luminescence, reflection and transmittance. The thickness of the films could be related to the preparation procedure. Transparent thin films have been prepared by dip-coating technique.

Nanocomposites materials generated from a spray

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Excitation mechanisms and effects of dopant concentration in Gd2O2S : Tb3+ phosphor

Gadolinium oxysulfide powders doped with different Tb3+ concentrations were prepared from sulfur vaporization on rare earths' basic carbonate precursors. Single-phase Gd2O2S samples were obtained, with Tb3+ doping up to 9 at%. The study of the excitation mechanisms revealed that the Tb3+ emission might occur after the direct Tb3+ excitation either by energy transfer from Gd3+ or from the phosphor host. The characteristic terbium emission lines were observed, resulting from the radiative decay from D-5(3) or D-5(4), to F-7(j) levels. The cross-relaxation phenomenon was observed and its effects on the materials emission color were discussed based on the CIE diagram. By using time-resolved spectroscopy, D-5(3) -> F-7(J) and D-5(4) -> F-7(J) transitions were separated. (c) 2007 Elsevier B.V. All rights reserved.

Y2O3:Eu3+ (5 mol%) with Ag nanoparticles prepared by citrate precursor

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)