Structural and optical properties of Er3+ doped SiO2-Al2O3-GeO2 compounds prepared by a simple route

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

PWA-diureasils organic-inorganic hybrids: photochromism and effect of the organic chain length

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

Multifunction hexagonal liquid-crystal containing modified surface TiO2 nanoparticles and terpinen-4-ol for controlled release

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

Luminescence of Eu3+ in the thin film heterojunction GaAs/SnO2

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Photoluminescence of the Eu-doped thin film heterojunction GaAs/SnO2 and rare-earth doping distribution

Tin dioxide (SnO2) thin films doped with Eu3+, are deposited by the sol-gel-dip-coating process on top of GaAs films, which is deposited by resistive evaporation on glass substrate. This heterojunction assembly presents luminescence from the rare-earth ion, unlike the SnO2 deposition directly on a glass substrate, where emissions from the Eu3+ transitions are absent. The Eu3+ transitions are clearly identified and are similar to the observation on SnO2 pressed powder (pellets), thermally treated at much higher temperatures. However, in the form of heterojunction films, the Eu emission comes along a broad band, located at higher energy compared to Eu3+ transitions, which is blue-shifted as the thermal annealing temperature increases. The size of nanocrystallites points toward quantum confinement or electron transfer between oxygen vacancies, originated from the disorder in the material, and trivalent rare-earth ions, which present acceptor-like character in this matrix. This electron transfer may relax for higher temperatures in the case of pellets, and the broad band is eliminated.

Structural properties of cerium doped siloxane-PMMA hybrid coatings with high anticorrosive performance

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

Correlation between structural and catalytic properties of copper supported on porous alumina for the ethanol dehydrogenation reaction

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A relationship between structural and electronic order-disorder effects and optical properties in crystalline TiO2 nanomaterials

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

Zirconium-methacrylate oxoclusters as new hybrid materials for the modification of epoxy systems

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nanostructured TiO2-based composites for light absorption

Metal oxidenanocomposites were prepared by two different routes: polyol and sol-gel. Characterization by X ray diffraction showed that the first processproducesdirectly a two-phase material, while the sol-gelpowder never showed second phase below 600 degrees C. Light spectroscopy of the treated powders indicated similarities for the processed materials. Although the overall material compositions are about the same, different structural characteristics are found for each processing. With the exception of Ti-Zn materials, all the double metal oxide powders showed higher absorbance than either TiO2 powder.

Heterojunction between Al2O3 and SnO2 thin films for application in transparent FET

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Investigation of photoinduced electrical properties in the heterojunction TiO2/SnO2

TiO2/SnO2 thin films heterostructures were grown by the sol-gel dip-coating technique. It was found that the crystalline structure of TiO2 depends on the annealing temperature and the substrate type. TiO2 films deposited on glass substrate, submitted to thermal annealing until 550 degrees C, present anatase structure, whereas films deposited on quartz substrate transform to rutile structure when thermally annealed at 1100 degrees C. When structured as rutile, this oxide semiconductor has very close lattice parameters to those of SnO2, making easier the heterostructure assembling. The electrical properties of TiO2/SnO2 heterostructure were evaluated as function of temperature and excitation with different light sources. The temperature dependence of conductivity is dominated by a deep level with energy coincident with the second ionization level of oxygen vacancies in SnO2, suggesting the dominant role of the most external layer material (SnO2) to the electrical transport properties. The fourth harmonic of a Nd:YAG laser line (4.65 eV) seems to excite the most external layer whereas a InGaN LED (2.75 eV) seems to excite electrons from the ground state of a quantized interfacial channel as well as intrabandgap states of the TiO2 layer.

Análise estrutural de aerogéis via espalhamento de luz a baixo ângulo

The sol-gel process is a method for obtaining vitreous or vitro-ceramic materials which, are prepared a sol and by drying the liquid phase. This technique has been used extensively for the preparation of glassy gels, films, fibers and particles from the hydrolysis and polycondensation reactions of metal alkoxides. The usual methods for drying are: evaporation drying (xerogels), freeze drying (criogéis) and via supercritical CO2 extraction (aerogels). In the present work, we studied the preparation of silica gels by the sol-gel process from the hydrolysis of alkoxides tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTS). The hydrolysis was promoted from GPTS and TEOS in proportion (4: 1) under acidic conditions. The hydrolysis reaction was promoted inside a Becker at room temperature. After hydrolyses the prepared sol had pH 2, and kept under mechanical agitation for a period of 1 hour. In order to accelerate the polycondensation reaction, the pH was corrected to a value near 5 by slowly adding NH4OH. Then the sols were leaked in sealed polycarbonate containers and maintained for 20 days at 40°C for gelation. Silica aerogels were prepared via supercritical CO2 extraction of the wet gel at temperature and pressure higher than 31°C and 74 atm, in an autoclave specially developed for the process. The structural characteristics were studied in the dry gel (aerogel). Aerogels were then characterized by nitrogen adsorption and small angle light scattering. The nitrogen adsorption data were analyzed for the determination of the BET specific surface (SBET), the total pore volume Vp, the pore mean size (lP=4Vp/SBET), the particle mean size (lS) and the pore size distribution (PSD). And the data from small angle light scattering were analyzed to determine the correlation function (γ'), the area per unit volume (S/V), average pore size (l ) and the average particle size...

Materiais híbridos de sílica/orgânico dopados com rodamina-B: estudo da luminescência e preparação de filmes finos para aplicações em fotônica

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

Preparação e caracterização óptica de filmes híbridos dopados com o azocorante Disperse Red 1

The Sol-gel process has facilitated the processing of Organic-Inorganic Hybrid Materials with several scientific applications and technologies. The hybrid combine the advantages of the Sol-gel process with specific characteristics of organic polymers, allowing processing of thin films without fractures or fissures. The incorporation of azo dyes in polymer matrices has been widely used in the investigation of optical properties. The azo dye Disperse Red (DR1) presents optical alterations when exposed to visible or ultraviolet light. The alterations occur due to transitions of their isomers, trans and cis, caused by photoisomerization, due to electronic transitions of azo group (-N=N-), presenting photochromic and/or photorefractive effects. The hybrid system used in this work is the precursor 3- Glycidoxypropyl-Trimethoxi-silane (GPTS), the Tetraethylorthosilicate (TEOS) and DR1 as a dopant. The characterizations were performed using absorption spectroscopy UV-Vis which allowed the identification of the absorption bands and its variations when the samples were treated thermally and/or illuminated by ultraviolet light