Papers by Author: Carlos J.R. Silva

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Authors: Julia T. Gonçalves, Victor I. Boev, Alexey Solovyev, Carlos J.R. Silva, M.J.M. Gomes
Abstract: Transparent hybrid organic-inorganic ureasil xerogels with embedded PbS nanoparticles were prepared by exposing the xerogels doped with lead (II) nitrate to hydrogen sulphide atmosphere. Absorbance spectrum of the nonocomposites showed well defined peaks at 560 nm and 370 nm attributed to 1s(v) - 1s(c) and 1s(v) - 2p(c) exciton transitions, respectively. After four days of thermal treatment at 50 °C under argon atmosphere the obtained materials showed enhanced photoluminescence response in the near infra-red region.
Authors: Victor I. Boev, Rute A. Sá Ferreira, Sonia S. Nobre, Carlos J.R. Silva, M.J.M. Gomes, Luís M. Liz-Marzán, Luís D. Carlos
Abstract: Photoluminescence of di-ureasil hybrids containing homogeneously dispersed Ag nanoparticles, covered with silica shells was investigated at room temperature and compared with emission of undoped hybrids. Metal-doped di-ureasils show a broad emission band in the blue spectral region similar to what has been observed in pure di-ureasils but with lower relative intensity. A broad minimum arises around 438 nm for Ag@SiO2 - containing di-ureasils which coincides with the peak of plasmon resonance band in the absorption spectrum. This behaviour can be attributed to inner filtering effect, which manifests itself as absorption by metal nanoparticles of light emitted from the matrix. Low-temperature time-resolved spectroscopy and lifetime measurements demonstrate that changes are induced in the time-scale behind the di-ureasil host emission when the nanoparticles are incorporated. In particular, the lifetime values for Ag@SiO2- doped di-ureasils are smaller than those measured for the undoped host, suggesting that energy transfer might exist between the hybrid's emitting centres (NH groups and siliceous nanodomains) and the nanoparticles.
Authors: Filomena Costa, Carlos J.R. Silva, António Maurício C. Fonseca, Isabel Neves, Ana P. Carvalho, João Pires, Manuela B. Carvalho
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