Luminescent nano-composites generated from a spray

The spray-pyrolysis (SP) synthesis technique has been employed to obtain SiO2:Eu3+ and gamma-AlOOH:Eu3+, It was possible to obtain sub-micrometric spherical particles of SiO2 with luminescent Eu3+ ions bonded to the silica surface or embedded in amorphous silica beads, by controlling the synthesis and annealing process. Boehmite y-AlOOH doped with Eu3+ nanoparticles were synthesized by SP at moderate temperature (200 degrees C) with Eu3+ ions bonded to the surface hydroxyls of the boehmite nanocrystals. Luminescent nanocomposites were obtained by controlled reaction of gamma-AlOOH:Eu3+ nanocrystals with ASN (asparagine). In these nano-composites, the Eu3+ are held at the surface of the boehmite nanocrystals and partially shielded from interactions with additional luminescence quenchers (hydroxyl groups, water molecules). (C) 2008 Elsevier B.V. All rights reserved.

BaMoO(4) powders processed in domestic microwave-hydrothermal: Synthesis, characterization and photoluminescence at room temperature

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Surface characterization of absorbing polymer films deposited on transparent glasses

PANI films were deposited on glass substrates by in-situ polymerization and characterized by UV-VIS spectroscopy and atomic force microscopy. A method is developed to accurately analyze ellipsometric data obtained for transparent glass substrates before and after modification with absorbing polymer films. Surface modification was made with an overlayer such as polyaniline ( PANI), which exhibits different optical properties by varying its oxidation state. First, the issue of using transparent substrates for ellipsometry studies was examined and then, spectroscopic ellipsometry was used to characterize absorbing overlayers on transparent glasses. The same methodologies of data analysis can be also applied to other absorbing films on transparent substrates, and deposited by different techniques.

Relationship between Crystal Shape, Photoluminescence, and Local Structure in SrTiO3 Synthesized by Microwave-Assisted Hydrothermal Method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Theoretical investigation of the electronic structure and absorption spectra of carbon cluster nanotubes

Electronic and optical properties of recently discovered single-shell carbon cluster nanotubes are studied through a semiempirical INDOCI method. The calculations are performed within the cluster model and include up to 196 atoms. The trend of the forbidden band gap with the number of carbon atoms (Cn n = 60, 10, 140) for a fixed diameter is analyzed. With increasing n the band gap decreases, as expected. The tubule, with diameter of 7.2Å (as C60-Buckyball) is predicted to be a metal or a narrow-gap semiconductor. The calculated absorption spectra of the clusters show a characteristic strong peak around 40,000 cm-1. Other features of the calculated UV-visible absorption spectra are discussed. © 1994.

Spectroscopy of InF3 based glasses containing a large amount of GdF3

Glass formation in the pseudo ternary system ZnF2-GdF3-BaF2-InF3 and other complex systems stabilized by NaF, CaF2, AlF3 and YF3 have been investigated. Samples with greater stability have been prepared and their properties measured. Optical absorption and emission spectra of Gd3+ ions doped glasses with 2, 4, 10 and 20% concentrations have been measured. Using the Judd-Ofelt theory and the experimental oscillator strengths, the Judd-Ofelt parameters have been calculated. The emission of Gd3+ ions from 6I and 6P has been detected and the lifetime has been measured.

Crystallization of fluorindate and fluorogallate glasses

Crystallization of binary InF3-MF2 and GaF3-MF2 (where M = Ba, Sr and Ca) glasses was studied. Characteristic temperatures and kinetic parameters E (activation energy) and n (Avrami exponent) were obtained. Stability against devitrification is discussed in terms of the above cited parameters and also of some others parameters proposed in literature. Optical properties (IR and upconversion emissions) are reported in different crystallized samples containing Nd3+. The main observation is that up conversion emission presents an enhanced sensibility to crystallization when compared to conventional emission. © 1997 Published by Elsevier Science B.V.

Transparent Er3+-activated lead fluorogermanate glass ceramics

Transparent glass ceramics containing β-PbF2:Er 3+ nanocrystals were obtained through appropriate thermal treatments of a glass of molar composition 60PbGeO3-10PbF2-30CdF 2 doped with 0.5 mol% Er3+. Their optical properties, as well as upconversion processes among erbium ions in the glass and glass ceramic matrix were studied. From absorption spectra, Judd-Ofelt parameters and radiative transition rates for several excited levels were calculated. Emission spectra in the visible and NIR regions were collected, and stimulated emission cross sections were obtained by McCumber theory for the 4F 13/2→4I15/2 transition at 1.5 μm. Red and green upconversion emissions were measured in glass and glass ceramics upon excitation at 980 nm; lifetimes were measured in order to assess the upconversion mechanisms.

Progress on holographic techniques to study photo-chemical reactions in solid state

In this paper it is presented recent developments in the heterodyne detection holographic techniques for studding photosensitive materials. The actual state of the technique allows simultaneous and independent measurement of the refractive index and of the absorption coefficient changes in photosensitive materials and their use to self-stabilize the fringe pattern. The modeling of the measured signal together with the fringe stabilization allow the long term-fitting of the optical properties and the study the photosensitive materials close to the saturation.

Electrooptic proprieties of layer-by-layer films of a azobenzene containing copolymer

The methacrylic copolymer functionalized with the azo chromophore 4-[N-ethyl-N-(2-hydroxiethyl)]-amino-2′-chloro-4-nitroazobenzene (MMADR13), in its polyelectrolyte form, can be used to fabricate thin films by the layer-by-layer (LbL) technique just if one alternates this anionic polyelectrolyte with a cationic polyelectrolyte such as poly(allylamine hydrochloride) (PAH). Since PAH does not present any particular optical functionality, the main final film feature will came from the side chain DR13 azo-chromophore group due to its large nonlinear optical properties and photoisomerization capabilities. This work reports the electrooptic activity of MMADR13/DR13 LBL films, which arises from the high hiperpolarizability about the azo side chain group.

Temporal evolution of sulfated zirconia sol-gel during dip coating: Analysis of mass drainage with time-varying refractive index

The formation of sulfated zirconia films from a sol-gel derived aqueous suspension is subjected to double-optical monitoring during batch dip coating. Interpretation of interferometric patterns, previously obscured by a variable refractive index, is now made possible by addition of its direct measurement by a polarimetric technique in real time. Significant sensitivity of the resulting physical thickness and refractive index curves (uncertainties of ±7 nm and ±0.005, respectively) to temporal film evolution is shown under different withdrawal speeds. As a first contribution to quantitative understanding of temporal film formation with varying nanostructure during dip coating, detailed analysis is directed to the stage of the process dominated by mass drainage, whose simple modeling with temporal t-1/2 dependence is verified experimentally. © 2006 Elsevier B.V. All rights reserved.

Physiological maturity of Cnidosculus quercifolius Pax & K. Hoffm. seeds

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

Plasmonic structures fabricated by interference lithography for sensor applications

In this work we demonstrate the use of holographic lithography for generation of large area plasmonic periodic structures. Submicrometric array of holes, with different periods and thickness, were recorded in gold films, in areas of about 1 cm2, with homogeneity similar to that of samples recorded by Focused Ion Beam. In order to check the plasmonic properties, we measured the transmission spectra of the samples. The spectra exhibit the typical surface plasmon resonances (SPR) in the infrared whose position and width present the expected behavior with the period of the array and film thickness. The shift of the peak position with the permittivity of the surrounding medium demonstrates the feasebility of the sample as large area sensors. © 2009 SPIE.

Lidar observation campaign of sugar cane fires and industrial emissions in the State of São Paulo, Brazil

Brazil has an important role in the biomass burning, with the detection of approximately 100,000 burning spots in a single year (2007). Most of these spots occur in the southern part of the Amazon basin during the dry season (from August to november) and these emissions reach the southeast of the country, a highly populated region and with serious urban air pollution problems. With the growing demand on biofuels, sugarcane is considerably expanding in the state of São Paulo, being a strong contributor to the bad air quality in this region. In the state of São Paulo, the main land use are pasture and sugarcane crop, that covers around 50% and 10% of the total area, respectively. Despite the aerosol from sugarcane burning having reduced atmospheric residence time, from a few days to some weeks, they might get together with those aerosol which spread over long distances (hundreds to thousands of kilometers). In the period of June through February 2010 a LIDAR observation campaign was carried in the state of São Paulo, Brazil, in order to observe and characterize optically the aerosols from two distinct sources, namely, sugar cane biomass burning and industrial emissions. For this purpose 2 LIDAR systems were available, one mobile and the other placed in a laboratory, both working in the visible (532 nm) and additionally the mobile system had a Raman channel available (607 nm). Also this campaign counted with a SODAR, a meteorological RADAR specially set up to detect aerosol echoes and gas-particle analyzers. To guarantee a good regional coverage 4 distinct sites were available to deploy the instruments, 2 in the near field of biomass burning activities (Rio Claro and Bauru), one for industrial emissions (Cubatão) and others from urban sources (São Paulo). The whole campaign provide the equivalent of 30 days of measurements which allowed us to get aerosol optical properties such as backscattering/extinction coefficients, scatter and LIDAR ratios, those were used to correlate with air quality and meteorological indicators and quantities. In this paper we should focus on the preliminary results of the Raman LIDAR system and its derived aerosol optical quantities. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Growth and morphology of eumelanin thin films - A future bioelectronic material?

We present a study on the thin film morphology and the optical properties of eumelanin resulting from different synthesis routes: the oxidation of tyrosine with hydrogen peroxide, the auto-oxidation of dihydroxyphenylanaline in water and its auto-oxidation in dimethyl sulfoxid. Atomic Force Microscopy images indicate that the presence of holes and particles depends on the eumelanin synthesis route and the substrate employed. Smooth films with very few defects could be obtained with eumelanin synthesized in dimethyl sulfoxide deposited on glass substrates. Our study shows that all eumelanin preparations are comparable in terms of thin film morphology on the submicrometer scale and UV-visible transmission properties. ©The Electrochemical Society.