Photoluminescence and cathodoluminescence of Eu:La2O3 nanoparticles synthesized by several methods

Abstract : Europium-doped La2O3 nanocrystalline powders with sizes ranging from 4 nm to 300 nm have been obtained by the modified Pechini, hydrothermal with conventional furnace, hydrothermal with microwave furnace, and precipitation with ultrasonic bath methods. X-ray diffraction techniques were used to study the evolution of the prepared gels towards the desired crystalline phase. We determined the size and the morphology of the nanoparticles by electronic microscopy. Finally, we studied and analyzed the luminescence properties of the trivalent europium in the hexagonal La2O3 nanocrystals by photoluminescence and cathodoluminescence

estudos artísticos

Como é característica fundadora do projeto CSO – criadores sobre outras obras – os artistas são aqui convidados a comunicar o seu conhecimento sobre outros artistas, dentro de um descentramento que toma os idiomas ibéricos como uma plataforma territorial de emergência, e de resistência, também. É uma área cultural periférica, alternativa, que se afirma em crescente grandeza. Dentro deste dispositivo comunicativo, a revista Croma delimita mais ainda o seu tema, nos artistas que de algum modo fazem incorporar a implicação social, a interação e a criação e formação de novos públicos como um dos componentes estruturantes da sua obra. Surgem na Croma obras intervenientes, que provocam, e que convocam, que estabelecem pontes, ou que as ameaçam. São obras em que a componente relacional (N. Bourriaud) ou formativa e integradora (P. Freire) assumem uma atualidade constante e renovada. Os artigos reunidos neste quinto número da Revista Croma propõem, no seu conjunto uma intenção de proximidade, de confronto com realidades, de inconformismo, de procura e de questionamento identitário. Dos seus múltiplos países e das suas diversificadas abordagens a variadas técnicas, os vinte e cinco artigos aqui apresentados complementam o poder do desassossego e da inquietação poética: os artistas falam connosco, através de outros artistas, que os souberam ver e ouvir.info:eu-repo/semantics/publishedVersio

Use of polymer as template in microwave synthesis of saponite. Study of several factors of influence

10.1016/j.clay.2013.10.027Several saponites were synthesized at pH = 8 by microwaves or conventional hydrothermal aging with different slurry dilutions (H2O/Si molar ratios of 250, 125 and 50) at 453 K under autogenic pressure. The influence of using a polymer as template, during the synthesis, and its molecular mass was investigated. The saponite prepared with medium dilution slurry by microwaves had the best incorporation of Al3 + in tetrahedral positions (AlT/AlO = 9.2), in agreement with its highest C.E.C. (0.87 mEq/g). Additionally, this sample showed the highest surface area (461 m2/g). In general, the increase of the slurry concentration and the presence of polymer improved the order in the tetrahedral sheet and decreased the amorphous silica content. The effect of polymer, on the stacking, was low but depended on the dilution and heat source (microwaves or conventional). The use of polymer and its molecular mass modified the saponite porosity and the incorporation of Al3 + in the tetrahedral sheet

Tuning the acidic and textural properties of ordered mesoporous silicas for their application as catalysts in the etherification of glycerol with isobutene

10.1016/j.cattod.2013.10.029Several silicas (MCM-41, SBA-15 and HMS) were acid-modi?ed by incorporating aluminium or by introducing phosphorus species or sulfonic groups. The modi?ed silicas maintained mesostructural ordering and a narrow pore size distribution. However, Their surface area and pore volume was lower than that of unmodi?ed samples. The incorporation of aluminum in the structure of MCM-41 and SBA-15 increased the amount of Brønsted acid sites, leading to greater catalytic activity (i.e., higher conversion values) for glycerol etheri?cation with isobutene than pure silicas, but their relatively weak acid strength resulted in low selectivity to di- and tri-tertiary butyl ethers of glycerol (h-GTBE). The introduction of phosphoric groups, with higher acidity strength, improved the selectivity to h-GTBE, and glycerol triether was detected in low amounts. Interestingly, HMS synthesized with dodecylamine and later sulfonated exhibited total conversion and 84% of selectivity to h-GTBE (26% to glycerol triether) after 24 h of reaction. The presence of textural mesoporosity in HMS reduced diffusion limitations, and consequently increased the incorporation of sulfonic groups and their accessibility, leading to higher catalytic activit

Aldol condensation of campholenic aldehyde and MEK over activated hydrotalcites

International audienc

Fast aging treatment for the synthesis of hydrocalumites using microwaves

10.1016/j.clay.2013.05.00