We report the results of the optical spectra modeling for hydrogenated amorphous silicon (a-Si:H) thin films produced for photovoltaic cell applications, which allowed us to accurately determine the material’s optical gap (Eg). While for thick films of a-Si:H, as well as for other amorphous semiconductors, Eg is normally estimated from a so called Tauc plot, this is hardly possible for thin films because of the interference effects. We developed a physically founded semianalytical model for the complex dielectric function of a-Si:H, valid below and above the optical gap and containing a small number of adjustable meaningful parameters, including Eg and the characteristic energy scales of the optical transition matrix element distribution and the joint density of states in the absorption tail region. With this model and using the transfer matrix formalism for multilayer optics, we have achieved a good agreement between the calculated and experimental transmittance spectra, which allowed us to self-consistently determine the values of the above parameters. We found that both Eg and the characteristic scale of the subgap absorption tail increase with the hydrogen addition. We have also determined the absorption rate spectra of the films, relevant to any optical spectroscopy of subgap states, such as the photothermal deflection spectroscopy and constant photocurrent measurements.

Abstract.A new design of decorative tungsten oxide coatings is presented. The coatings were deposited with gradient refraction index by magnetron sputtering from a tungsten target and pulsing the reactive gas. The controlled injection of the reactive gas can produce a gradient concentration profile from pure tungsten to tungsten trioxide determining the final apparent colour of the coating. A dynamic sputtering model was built to simulate the coating growth during the reactive gas pulsing which was validated by the direct measurement of the oxygen content gradient in the deposited coatings. Finally these results were used for an optical model allowing describing the optical properties of the deposited tungsten oxide layer, again validated by experimental analysis. This procedure allows depositing coatings with a desired colour by using the models for finding the optimal oxygen pulse parameters. This proposed method can be easily applied to almost any metal/metal oxide system.

We present the theory of the thermally activated photoluminescence upconversion, also known as anti‐Stokes photoluminescence (ASPL), based on the quantum dot (QD) polaron effect and explaining all the principal features of the ASPL in colloidal solutions of chemically grown nanocrystals (NCs). The results obtained by Monte‐Carlo simulations reproduce all the experimentally observed ASPL trends in colloidal NC solutions and are being extended to dense QD systems, such as films composed by layers of closely packed NCs (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Resumo A obra “Iconografia Selecta da Flora Portuguesa”, de Gonçalo Sampaio (botânico) e Sara Cabral Ferreira (ilustradora), foi editada pela primeira vez em 1949. Contendo cento e cinquenta estampas de espécies da flora portuguesa, este livro destacou-se na literatura botânica nacional, embora fosse uma edição póstuma e incompleta. Os seus desenhos originais, realizados em técnica monotonal (tinta-da-china), integram atualmente a coleção de ilustração científica do Museu de História Natural e da Ciência da Universidade do Porto (MHNC-UP). Uma vez que nenhum texto, além do prefácio e dos nomes científicos das plantas, acompanha as imagens no livro, as razões que sustentaram a seleção das espécies a ilustrar, assim como a sua relevância botânica, permaneceram desconhecidas. Neste artigo, tentamos reconstruir a história desta iconografia, com base na análise de documentos epistolares e manuscritos. Focamo-nos também na importância da ilustração científica e no seu uso como ferramenta para a representação visual de espécies botânicas e para a comunicação de ciência. Assim, analisamos a metodologia empregue, quer na tipologia do arquétipo, quer na técnica de execução, bem como as eventuais restrições que conduziram a essas opções. Ao analisar estas ilustrações botânicas da primeira metade do séc. XX, procurou-se ainda explorar a pertinência destas iconografias em estudos botânicos anteriores e contemporâneos, bem como o seu potencial enquanto instrumentos de difusão de ciência. Palavras-chave: Ilustração Científica; Flora Portuguesa; História da Botânica. Abstract The book “Iconografia Selecta da Flora Portuguesa”, by Gonçalo Sampaio (botanist) and Sara Cabral Ferreira (illustrator), was first published in 1949. Containing one hundred and fifty prints of Portuguese flora species, this book stood out in the national botanical literature, although it was a posthumous and incomplete edition. The original book drawings, made in a monotonic technique, are part of the scientific illustration collection of the Museum of Natural History and Science of the University of Porto (MHNC- UP). Since no text, besides preface and the scientific names of the plants, accompanies the images in the book, the reasons which supported the selection of the species to be illustrated, as well as their botanical relevance, remained unknown. In this article, we attempted to reconstruct the history of this iconography, based on the analysis of epistolary documents and manuscripts. We also focus on the importance of scientific illustration and on its usage as a tool for the visual representation of botanical species and for science communication. Therefore, we analyzed the methodology used both in the typology of the archetype as in the execution techniques, as well as the restrictions that led to those options. By analyzing these botanical drawings of the first half of the twentieth century, it was also sought to explore the relevance of these iconographies in earlier and modern botanical studies, as well as their potential as instruments of diffusion of science. Keywords: Scientific Illustration; Portuguese Flora; History of Botany.