Synthesis of a neodymium-quinolate complex for near-infrared electroluminescence applications

A structurally pure, near-infrared emissive Nd-(5,7-dichloro-8-hydroxyquinoline)4 tetrakis complex has been synthesized. When incorporated as a dopant in the blue emissive, hole conducting polymer poly(N-vinylcarbazole), PVK, sensitized neodymium ion emission was observed following photo-excitation of the polymer host. OLED devices were fabricated by spin-casting layers of the doped polymer onto glass/indium tin oxide (ITO)/3,4-polyethylene-dioxythiophene-polystyrene sulfonate (PEDOT) substrates. An external quantum efficiency of 1 x 10(-3)% and a near-infrared irradiance of 2.0 nW/mm(2) at 25 mA/mm(2) and 20 V was achieved using glass/ITO/PEDOT/ PVK:Nd-(5,7-dichloro-8-hydroxyquinoline)(4)/Ca/Al devices. (C) 2007 Elsevier B.V. All rights reserved.

The Co-Entrapment of a Homogeneous Catalyst and an Ionic Liquid by a Sol-gel Method: Recyclable Ionogel Hydrogenation Catalysts

Molecular hydrogenation catalysts have been co-entrapped with the ionic liquid [Bmim]NTf(2) inside a silica matrix by a sot-gel method. These catalytic ionogels have been compared to simple catalyst-doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh-doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X-ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.

Mat��rias-primas da plataforma do Mondego para cer��mica

O presente trabalho divulga os resultados dos estudos levados a efeito nas mat��rias-primas argilosas que se integram tipologicamente na argila comum, ocorrentes na designada Plataforma do Mondego, Centro de Portugal, na regi��o entre Miranda do Corvo, a SW, e T��bua, a NE. Para tal realizou-se a cartografia superficial dos sedimentos continentais do Cret��cico e do Terci��rio, a�� preservados, estabeleceram-se as colunas sedimentares, a n��vel regional e a n��vel local, nas ��reas de maior potencial reconhecido e, caracterizaram-se as mat��rias-primas argilosas amostradas, em termos de composi����o, textura e aptid��o cer��mica, objectivando a defini����o das zonas das jazidas com maior interesse industrial. A informa����o obtida e compilada, relativa ao caulino e ao feldspato �� tamb��m apresentada, com vista a uma percep����o da potencialidade destas mat��riasprimas cer��micas ocorrentes na ��rea. O estudo de caracteriza����o dos materiais argilosos investigados teve como base 53 amostras obtidas em seis regi��es da Plataforma do Mondego aqui definidas por motivo de organiza����o do trabalho, segundo os crit��rios geogr��fico e geotect��nico. As forma����es de C��ja e de Campelo, do Terci��rio, constituem as unidades onde ocorrem lit��tipos produtivos, em termos de mat��ria-prima para a Cer��mica de Barro Vermelho ou Cer��mica de Constru����o. Relativamente ��s caracter��sticas texturais e composicionais, em s��ntese, apresentam-se os factos relevantes seguintes: A mat��ria-prima argilosa existente na ��rea estudada materializa, granulometricamente, na maioria das amostras, silte, caindo os n��veis amostrados com maior percentagem de argila, no dom��nio do silte argiloso. O d��fice em frac����o argila implica limita����es quanto �� possibilidade de diversifica����o de produtos cer��micos fabricados com estas mat��rias-primas tal-qual. Os diferentes m��todos anal��ticos utilizados na caracteriza����o mineral��gica dos materiais amostrados confirmaram uma composi����o em termos dos minerais argilosos, consistindo de ilite/mica (em geral, o mais abundante), caulinite e esmectite, interestratificados e clorite. Os minerais n��o argilosos s��o quartzo (predominante), feldspato (sobretudo pot��ssico) e hematite, com uma representa����o baixa. A mineralogia da frac����o inferior a 2��m das amostras, n��o difere das amostras totais, salvo no teor mais elevado dos minerais argilosos e acentuada redu����o dos minerais n��o argilosos. Os resultados da an��lise qu��mica por fluoresc��ncia de raios X das amostras integrais correlacionam-se com as caracter��sticas mineral��gicas observadas atrav��s das t��cnicas anal��ticas utilizadas. No respeitante ��s propriedades e comportamento cer��mico verifica-se: Os par��metros relacionados com a plasticidade indicam que parte das pastas elaboradas com estes materiais argilosos t��m uma trabalhabilidade aceit��vel, mas existem problemas de conforma����o e acentuada retrac����o num n��mero significativo de amostras, devido �� elevada plasticidade da maioria das amostras. A extrus��o �� satisfat��ria a ��ptima. A RMF e a retrac����o em seco assumem valores, respectivamente, moderados a baixos e moderados, embora seja necess��rio ter em conta o procedimento de extrus��o dos provetes, sem dispositivo de v��cuo. Todas as amostras foram sujeitas a cozedura a 900��C, e um conjunto seleccionado foi cozido a 1000��C e a 1100��C. As fases mineral��gicas ocorrentes ap��s cozeduras a 900��C e 1100��C foram identificadas num conjunto de amostras, tendo-se evidenciado a coer��ncia dessas fases, com a mineralogia das amostras em seco. Ap��s cozedura a 900��C, os valores de RMF das amostras satisfazem geralmente os valores m��nimos, exigidos para o fabrico de tijolo, abobadilha e, com alguma frequ��ncia, de telha, como j�� se verificava com os valores daquela propriedade em seco. Os valores de retrac����o seco-cozido s��o em geral, modestos. A capacidade de absor����o de ��gua �� maioritariamente elevada. A forma����o de vidro, sobretudo, condiciona o comportamento destas propriedades por cozedura dos provetes a 1000��C e a 1100��C. A colora����o predominante em cru das mat��rias-primas argilosas amostradas �� amarelo acastanhado a castanho avermelhado. Ap��s cozedura a 900��C, h�� um acentuado escurecimento e incremento no grau de vermelho. As cozeduras a 1000��C e 1100��C promovem escurecimento gradual, com ligeira influ��ncia na cor. O comportamento dos provetes ap��s as cozeduras cer��micas revelou-se homog��neo a cada uma das respectivas temperaturas, n��o se registando tamb��m defeitos significativos, nem efloresc��ncias. A an��lise das amostras em termos composicionais e tecnol��gicos permitiu destacar as principais caracter��sticas e aspectos distintivos das mat��riasprimas, nas diferentes regi��es definidas objectivando as diferentes potencialidades cer��micas. Nesta abordagem comparativa foram consideradas s�� as amostras dos campos silte e silte arenoso, por serem aquelas com maior interesse para a Cer��mica de Constru����o. Nas colunas sedimentares das regi��es de T��bua e Santa Quit��ria constata-se a ocorr��ncia de dois ritmos de sedimenta����o, que embora assumam caracter��sticas espec��ficas em cada regi��o, t��m aspectos composicionais e tecnol��gicos em comum, traduzindo melhor aptid��o cer��mica os ritmos inferiores. A conjuga����o da cartografia realizada com os estudos laboratoriais permite concluir que as regi��es de T��bua e de Santa Quit��ria ser��o as que t��m maior potencial por explorar, em mat��ria-prima para Cer��mica de Constru����o, apesar da primeira j�� ser intensamente explorada. Na regi��o de T��bua, as amostras t��m como fases mineral��gicas principais ilite e quartzo na mesma propor����o m��dia (35%) e caulinite (m��dia=19%) que regista enriquecimento significativo na frac����o argila (m��dia=38%). As argilas desta regi��o registam a cor em cru mais vermelha e pH mais ��cido observados. O ritmo de sedimenta����o inferior, com esmectite e interestratificados e ligeiramente menos quartzoso, apresenta melhores propriedades cer��micas. A composi����o mineral��gica m��dia das amostras da regi��o de Santa Quit��ria �� pr��xima daquela da regi��o de T��bua, mas menos caulin��tica, em especial na sequ��ncia inferior, na qual o teor m��dio de caulinite na frac����o argila (7%) �� o mais baixo observado. Na regi��o de C��ja ��� Arganil, a actividade extractiva �� significativa na bacia de C��ja. Aqui, a explora����o de novas ��reas potenciais �� condicionada pela cobertura conglomer��tica e por estruturas tect��nicas e n��o tect��nicas relacionadas com comportamento pl��stico. Na restante ��rea desta regi��o, os recursos argilosos s��o penalizados por material areno-conglomer��tico. As amostras desta regi��o distinguem-se das restantes a n��vel textural pela maior frac����o areia e mineralogicamente pela presen��a de clorite, teor reduzido de caulinite e elevado de feldspato. As potencialidades em barro vermelho na regi��o de Sanguinheda n��o ser��o significativas, pois a Forma����o de C��ja �� predominantemente arc��sica e a Forma����o de Campelo pouco espessa e conglomer��tica. As argilas com melhor aptid��o cer��mica foram amostradas na regi��o de Miranda do Corvo ��� Lous��. Na composi����o, estas amostras s��o as que cont��m maior frac����o de argila, maior teor de ilite e caulinite e menor de argilas expansivas. Registam os melhores valores nas caracter��sticas tecnol��gicas, nomeadamente a RMF e absor����o de ��gua. A consist��ncia dos grupos amostrais e ritmos definidos em termos composicionais e tecnol��gicos �� corroborada pelas t��cnicas de an��lise estat��stica multivariada aplicadas, que os identificam. As condi����es de amostragem na regi��o de T��bua, permitiram a elabora����o de uma coluna tipol��gica, na qual, a partir de uma caracteriza����o expedita de amostras �� poss��vel identificar a sua afinidade com os ritmos argilosos definidos e, consequentemente, a sua situa����o na coluna sedimentar regional e aptid��o cer��mica. A cartografia dos recursos argilosos potenciais, elaborada �� escala 1:25.000, constitui um dos objectivos principais deste trabalho e nela constam unidades litol��gicas, nas quais s��o diferenciadas unidades argilosas tendo tamb��m em considera����o a tipologia e guias mineral��gicos resultantes da caracteriza����o das amostras. As caracter��sticas composicionais destas unidades denotam diferente aptid��o cer��mica e, portanto, permitem salientar as zonas com maior interesse econ��mico.

Electromechanical properties of engineered lead free potassium sodium niobate based materials

K0.5Na0.5NbO3 (KNN), is the most promising lead free material for substituting lead zirconate titanate (PZT) which is still the market leader used for sensors and actuators. To make KNN a real competitor, it is necessary to understand and to improve its properties. This goal is pursued in the present work via different approaches aiming to study KNN intrinsic properties and then to identify appropriate strategies like doping and texturing for designing better KNN materials for an intended application. Hence, polycrystalline KNN ceramics (undoped, non-stoichiometric; NST and doped), high-quality KNN single crystals and textured KNN based ceramics were successfully synthesized and characterized in this work. Polycrystalline undoped, non-stoichiometric (NST) and Mn doped KNN ceramics were prepared by conventional ceramic processing. Structure, microstructure and electrical properties were measured. It was observed that the window for mono-phasic compositions was very narrow for both NST ceramics and Mn doped ceramics. For NST ceramics the variation of A/B ratio influenced the polarization (P-E) hysteresis loop and better piezoelectric and dielectric responses could be found for small stoichiometry deviations (A/B = 0.97). Regarding Mn doping, as compared to undoped KNN which showed leaky polarization (P-E) hysteresis loops, B-site Mn doped ceramics showed a well saturated, less-leaky hysteresis loop and a significant properties improvement. Impedance spectroscopy was used to assess the role of Mn and a relation between charge transport ��� defects and ferroelectric response in K0.5Na0.5NbO3 (KNN) and Mn doped KNN ceramics could be established. At room temperature the conduction in KNN which is associated with holes transport is suppressed by Mn doping. Hence Mn addition increases the resistivity of the ceramic, which proved to be very helpful for improving the saturation of the P-E loop. At high temperatures the conduction is dominated by the motion of ionized oxygen vacancies whose concentration increases with Mn doping. Single crystals of potassium sodium niobate (KNN) were grown by a modified high temperature flux method. A boron-modified flux was used to obtain the crystals at a relatively low temperature. XRD, EDS and ICP analysis proved the chemical and crystallographic quality of the crystals. The grown KNN crystals exhibit higher dielectric permittivity (29,100) at the tetragonal-to-cubic phase transition temperature, higher remnant polarization (19.4 ��C/cm2) and piezoelectric coefficient (160 pC/N) when compared with the standard KNN ceramics. KNN single crystals domain structure was characterized for the first time by piezoforce response microscopy. It could be observed that <001> - oriented potassium sodium niobate (KNN) single crystals reveal a long range ordered domain pattern of parallel 180�� domains with zig-zag 90�� domains. From the comparison of KNN Single crystals to ceramics, It is argued that the presence in KNN single crystal (and absence in KNN ceramics) of such a long range order specific domain pattern that is its fingerprint accounts for the improved properties of single crystals. These results have broad implications for the expanded use of KNN materials, by establishing a relation between the domain patterns and the dielectric and ferroelectric response of single crystals and ceramics and by indicating ways of achieving maximised properties in KNN materials. Polarized Raman analysis of ferroelectric potassium sodium niobate (K0.5Na0.5)NbO3 (KNN) single crystals was performed. For the first time, an evidence is provided that supports the assignment of KNN single crystals structure to the monoclinic symmetry at room temperature. Intensities of A���, A��� and mixed A���+A��� phonons have been theoretically calculated and compared with the experimental data in dependence of crystal rotation, which allowed the precise determination of the Raman tensor coefficients for (non-leaking) modes in monoclinic KNN. In relation to the previous literature, this study clarifies that assigning monoclinic phase is more suitable than the orthorhombic one. In addition, this study is the basis for non-destructive assessments of domain distribution by Raman spectroscopy in KNN-based lead-free ferroelectrics with complex structures. Searching a deeper understanding of the electrical behaviour of both KNN single crystal and polycrystalline materials for the sake of designing optimized KNN materials, a comparative study at the level of charge transport and point defects was carried out by impedance spectroscopy. KNN single crystals showed lower conductivity than polycrystals from room temperature up to 200 ��C, but above this temperature polycrystalline KNN displays lower conductivity. The low temperature (T < 200 ��C) behaviour reflects the different processing conditions of both ceramics and single crystals, which account for less defects prone to charge transport in the case of single crystals. As temperature increases (T > 200 ��C) single crystals become more conductive than polycrystalline samples, in which grain boundaries act as barriers to charge transport. For even higher temperatures the conductivity difference between both is increased due to the contribution of ionic conduction in single crystals. Indeed the values of activation energy calculated to the high temperature range (T > 300 ��C) were 1.60 and 0.97 eV, confirming the charge transport due to ionic conduction and ionized oxygen vacancies in single crystals and polycrystalline KNN, respectively. It is suggested that single crystals with low defects content and improved electromechanical properties could be a better choice for room temperature applications, though at high temperatures less conductive ceramics may be the choice, depending on the targeted use. Aiming at engineering the properties of KNN polycrystals towards the performance of single crystals, the preparation and properties study of (001) ��� oriented (K0.5Na0.5)0.98Li0.02NbO3 (KNNL) ceramics obtained by templated grain growth (TGG) using KNN single crystals as templates was undertaken. The choice of KNN single crystals templates is related with their better properties and to their unique domain structure which were envisaged as a tool for templating better properties in KNN ceramics too. X-ray diffraction analysis revealed for the templated ceramics a monoclinic structure at room temperature and a Lotgering factor (f) of 40% which confirmed texture development. These textured ceramics exhibit a long range ordered domain pattern consisting of 90�� and 180�� domains, similar to the one observed in the single crystals. Enhanced dielectric (13017 at TC), ferroelectric (2Pr = 42.8 ��C/cm2) and piezoelectric (d33 = 280 pC/N) properties are observed for textured KNNL ceramics as compared to the randomly oriented ones. This behaviour is suggested to be due to the long range ordered domain patterns observed in the textured ceramics. The obtained results as compared with the data previously reported on texture KNN based ceramics confirm that superior properties were found due to ordered repeated domain pattern. This study provides an useful approach towards properties improvement of KNN-based piezoelectric ceramics. Overall, the present results bring a significant contribution to the pool of knowledge on the properties of sodium potassium niobate materials: a relation between the domain patterns and di-, ferro-, and piezo-electric response of single crystals and ceramics was demonstrated and ways of engineering maximised properties in KNN materials, for example by texturing were established. This contribution is envisaged to have broad implications for the expanded use of KNN over the alternative lead-based materials.

UV optical absorption spectra analysis of beryl crystals from Brazil

The spectral decomposition analysis was applied to the optical absorption spectra of green and colorless beryl crystals from the Brazilian Eastern Pegmatitic province in the natural state, Submitted to heat treatment and irradiated with UV light The attributions of the lines were made taking into account highly accurate quantum mechanical calculations The deconvolution of the green beryl spectra revealed four lines, two of them around 12,000 cm(-1) (1 5eV) and two of them around 34,000 cm(-1) (4.2 eV) attributed to Fe(2+) and Fe(3+), respectively The deconvolution of the colorless beryl spectra without any treatment, after heating and for the same heat treatment followed by UV light irradiation revealed five lines The analysis of ratio relations showed that the lines at 36,400 cm(-1) (4.5 eV) and 41,400 cm(-1) (5 1 eV) belongs to a single defect attributed to a silicon dangling bond defect (=Si). Discussions and comparison with reported defects in quartz have supported the allocation of the lines at 61,000 cm(-1) (7.6 eV) and 43,800 cm(-1) (5 4 eV) to diamagnetic oxygen vacancy defect ( Si-Si ) and unrelaxed ( Si Si ) defect, respectively Finally, the line at 39.100 cm(-1) (4.8 eV), quite polarized along the c-axis, was attributed to a (Fe(2+) OH(-)) defect in the structural channels (C) 2009 Elsevier B V All rights reserved

Beneficiamentos da cinza de casca de arroz residual com vistas �� produ����o de cimento composto e/ou pozol��nico

A cinza de casca de arroz �� um res��duo agro-industrial decorrente do processo de queima da casca de arroz, sendo largamente encontrada no Rio Grande do Sul, pois, historicamente, este Estado �� o maior produtor de arroz no Brasil, com cerca de 45% da produ����o nacional. Empregada como fonte de energia, a casca de arroz �� queimada em diversas empresas; algumas, devido �� sua natureza, incorporam a cinza ao produto, mas a maioria n��o encontra outro destino que n��o o descarte em forma de aterro, criando, assim, um problema ambiental de polui����o do solo, do ar e de rios e c��rregos. No entanto, devido �� presen��a de elevado percentual de s��lica (SiO2) na sua constitui����o, a cinza de casca de arroz pode ter v��rios empregos. Na constru����o civil, pode ser empregada como pozolana, conforme v��rios estudos j�� v��m demonstrando. Por��m, encontra restri����es por motivos como sua cor escura, que confere aos cimentos, argamassas e concretos aos quais �� adicionada, uma colora����o tamb��m escura, e a falta de uniformidade apresentada em termos de caracter��sticas qu��micas e, principalmente, mineral��gicas. A cor escura n��o �� um problema de ordem t��cnica, mas est��tica e de aceita����o no mercado. J�� a composi����o mineral��gica est�� associada �� atividade pozol��nica e a falta de uniformidade do material dispon��vel implica na incerteza do grau de reatividade. Este trabalho teve o objetivo de verificar a viabilidade t��cnica do emprego de cinzas de casca de arroz residuais na confec����o de cimentos Portland composto e/ou pozol��nico, a partir de beneficiamentos das mesmas, que associam tratamentos f��sicos, qu��micos e/ou t��rmicos, os quais t��m como finalidade reverter e/ou minimizar os aspectos negativos citados. Para tanto, foram empregadas tr��s cinzas de casca de arroz, oriundas de diferentes processos de produ����o e com composi����es mineral��gicas distintas. Ap��s definidos os tratamentos a serem aplicados, atrav��s de sele����o pelos crit��rios de cor e composi����o mineral��gica, as cinzas tratadas foram avaliadas quanto �� sua pozolanicidade, pelo ��ndice de Atividade Pozol��nica (IAP) da NBR 5752 e tamb��m por um IAP alterado, proposto neste trabalho. A produ����o de cimentos com CCA beneficiada se deu a partir de um cimento base com substitui����o por CCA, em massa e em diferentes percentuais. Tais cimentos foram avaliados quanto �� resist��ncia �� compress��o, aos tempos de pega, �� pozolanicidade e �� expansibilidade a quente. A an��lise dos dados obtidos indica que os tratamentos propostos e/ou a associa����o deles resultam em beneficio no desempenho das cinzas, em pelo menos um dos v��rios aspectos considerados. A presente pesquisa permite concluir que as CCA residuais t��m potencial para serem empregadas na produ����o de cimentos, tanto aquelas menos cristalinas, quanto as mais cristalinas. Para tanto, devem ser beneficiadas, sendo pelo menos submetidas a tratamento f��sico para redu����o de sua granulometria. Se outros objetivos forem pretendidos, como colora����o clara, os tratamentos t��rmico ou qu��mico podem ser empregados.

Reuse of sugarcane bagasse ash (SCBA) to produce ceramic materials

Sugarcane bagasse ash (SCBA) is a residue resulting from the burning of bagasse in boilers in the sugarcane/alcohol industry. SCBA has a very high silica concentration and contains aluminum, iron, alkalis and alkaline earth oxides in smaller amounts. In this work, the properties of sintered ceramic bodies were evaluated based on the concentration of SCBA, which replaced non-plastic material. The ash was mixed (up to 60 wt%) with a clayed raw material that is used to produce roof tiles. Prismatic probes were pressed and sintered at different temperatures (up to 1200 degrees C). Technological tests of ceramic probes showed that the addition of ash has little influence on the ceramic properties up to 1000 C. X-ray diffraction and thermal analysis data showed that, above this temperature the ash participates in the sintering process and in the formation of new important phases. The results reported show that the reuse of SCBA in the ceramic industry is feasible. (C) 2011 Elsevier Ltd. All rights reserved.

Petrologia do magmatismo tardi-brasiliano no Maci��o S��o Jos�� de Campestre(RN/PB), com ��nfase no Pl��ton Alcalino Caxexa

The area studied is located on the north-easternmost portion of the Borborema Province, on the so-called S��o Jos�� de Campestre Massif, States of RN and PB, Northeast Brazil. Field relations and petrographic, geochemical and isotope data permitted the separation of five suites of plutonic rocks: alkali-feldspar granite (Caxexa Pluton), which constitutes the main subject of this dissertation, amphibole-biotite granite (Cabe��udo Pluton), biotite microgranite, gabbronorite to monzonite (Basic to Intermediate Suite) and aluminous granitoid. The Caxexa Pluton is laterally associated to the Rem��gio Pocinhos Shear Zone, with its emplacement along the mylonitic contact between the gneissic basement and the micashists. This pluton corresponds to a syntectonic intrusion elongated in the N-S direction, with about 50 km2 of outcropping surface. It is composed exclusively of alkali-feldspar granites, having clinopyroxene (aegirine-augite and hedenbergite), andradite-rich garnet, sphene and magnetite. It is classified geochemically as high silica rocks (>70 % wt), metaluminous to slightly peraluminous (normative corindon < 1%), with high total alkalis (>10% wt), Sr, iron number (#Fe=90-98) and agpaitic index (0.86-1.00), and positive europium anomaly. The Cabe��udo Pluton is composed of porphyritic rocks, commonly containing basic to intermediate magmatic enclaves often with mingling and mixing textures. Petrographically, it presents k-feldspar and plagioclase phenocrysts as the essential minerals, besides the accessories amphibole, biotite, sphene and magnetite. It is metaluminous and shows characteristics transitional between the calc-alkaline and alkaline series (or monzonitic subalkaline). Its REE content is greater than those ones of the Caxexa Pluton and biotite microgranite, and all spectra have negative europium anomalies. The biotite microgranites occur mainly on the central and eastern portion of the mapped area, as dykes and sheets with decimetric thickness, hosted principally in orthogneisses and micashists. Their field relationships as regards the Caxexa and Cabe��udo plutons suggested that they are late-tectonic intrusions. They are typically biotite granites, having also sphene, amphibole, allanite, opaques and zircon in the accessory assemblage. Geochemically they can be distinguished from the porphyritic types because the biotite microgranites are more evolved, peraluminous, and have more fractionated REE spectra. The Basic to Intermediate rocks form a volumetrically expressive elliptical, kilometric scale body on the Southeast, as well as sheets in micashists. They are classified as gabbronorites to monzonites, with the two pyroxenes and biotite, besides subordinated amounts of amphibole, sphene, ilmenite and allanite. These rocks do not show a well-defined geochemical trend, however they may possibly represent a monzonitic (shoshonitic) series. Their REE spectra have negative europium anomalies and REE contents greater than the other suites. The aluminous granitoids are volumetrically restricted, and have been observed in close association with migmatised micashists bordering the gabbronorite pluton. They are composed of almandine-rich garnet, andalusite, biotite and muscovite, and are akin to the peraluminous suites. Rb-Sr (whole rock) and Sm-Nd (whole-rock and mineral) isotopes furnished a minimum estimate of the crystallization (578��14 Ma) and the final resetting age of the Rb-Sr system (536��4 Ma) in the Caxexa Pluton. The aluminous granitoid has a Sm-Nd garnet age similar to that one of the Caxexa Pluton, that is 574��67 Ma. The strong interaction of shear bands and pegmatite dykes favoured the opening of the Rb-Sr system for the Caxexa Pluton and biotite microgranite. The amphibole-plagioclase geothermometer and the Al-in amphibole geobarometer indicate minimum conditions of 560��C and 7 kbar for the Cabe��udo Pluton, 730��C and 6 kbar for the microgranite and 743��C and 5 kbar for the basic to intermediate suite. The Zr saturation geothermometer reveals temperatures of respectively 855��C, 812��C and 957��C for those suites, whereas the Caxexa Pluton shows temperatures of around 757��C. The Caxexa, Cabe��udo and microgranites suites crystallized under high fO2 (presence of magnetite). On the other hand, the occurrence of ilmenite suggests less oxidant conditions in the basic to intermediate suite. Field relations demonstrate the intrusive character of the granitoids into a tectonically relatively stable continental crust. This is corroborated by petrographic and geochemical data, which suggest a late- or post-collisional tectonic context. It follows that the generation and emplacement of those granitoid suites is related to the latest events of the Brasiliano orogeny. Finally, the relationships between eNd (600 Ma), TDM (Nd) and initial Sr isotope ratio (ISr) do not permit to define the precise sources of the granitoids. Nevertheless, trace element modelling and isotopic comparisons suggest the participation of the metasomatised mantle in the generation of these suites, probably modified by different degrees of crustal contamination. In this way, a metasomatised mantle would not be a particular characteristic of the Neoproterozoic lithosphere, but a remarkable feature of this portion of the Borborema Province since Archaean and Paleoproterozoic times.

Local Er(III) environment in luminescent titanosilicates prepared from microporous precursors

The local environment of Er3+ ions in microporous titanosilicate ETS-10 and in synthetic narsarsukite and glassy materials obtained by calcination of ETS-10 has been investigated by EXAFS, Raman and photoluminescence spectroscopies. Er L-III-edge EXAFS studies of Er3+-doped ETS-10 support the view that the exchanged Er3+ ions reside close to the (negatively charged) TiO6 octahedra. In ETS-10, Er3+ is partially bonded to framework oxygen atoms and hydration water molecules. The Er...Ti distance (3.3 Angstrom) is similar to the Na...Ti distances (3.15-3.20 Angstrom) reported previously for Na-ETS-10. Although the exact location of the ErO6 units within the host structure of Er3+-doped synthetic narsarsukite is still an open question, it is most likely that Er3+ substitutes Ti4+ rather than Na+ ions. EXAFS spectroscopy indicates that no significant clustering of erbium atoms occurs in the titanosilicate samples studied. Evidence for the insertion of Er3+ ions in the framework of narsarsukite has been obtained by Raman spectroscopy. This is indicated by the increasing full-width at half-maximum (FWHM) of the 775 cm(-1) peak and the increasing intensity of the anatase peaks as the erbium content increases. In addition, as the narsarsukite Er3+ content increases a band at ca. 515 cm(-1) firstly broadens and subsequently a new peak appears at ca. 507 cm(-1).Er3+-doped narsarsukite exhibits a characteristic local vibrational frequency, (h) over bar omega ca. 330 cm(-1), with an electron-phonon coupling, g ca. 0.2, which constitutes additional evidence for framework Er3+ insertion. The number of lines in the infrared emission spectrum of synthetic narsarsukite indicates the presence of two optically-active erbium centres with very similar local environments and an average I-4(13/2) lifetime of 7.8 +/- 0.2 ms.

Stoichiometry unbalance and photoluminescence emission in Ga1-XAsX films prepared by flash evaporation

Both narrow and broad photoluminescence bands were observed in Ga1-XAsX films prepared by flash evaporation of polycrystalline GaAs containing native C impurities. The observed narrow crystalline-like bands are similar to band-to-band and C acceptor impurity emissions in crystalline GaAs. The narrow bands are evidence that the As excess favors the PL active GaAs crystallite formation in films deposited onto silicon (10 0) substrate, even when the As excess is very large (X = 0.84). This favoring is not observed in twin samples grown on silica glass substrates nor on Ga rich samples, indicating the important role of the combined effect of the As excess and Si substrate in the GaAs crystallite formation. The broad amorphous-like bands were observed in Ga rich and in moderately As rich samples. The photoluminescence emission is compared with the microstructure of the material as determined from the micro-Raman, absorption edge and reflectance measurements. The volume fraction of the crystallites formed is small and PL emission indicates that the crystallite electronic quality is much better than the ones formed heat treating films grown on silica glass substrates. (C) 2004 Elsevier B.V. All rights reserved.

Clustering of rare earth in glasses, aluminum effect: experiments and modeling

Luminescent spectra of Eu3+-doped sol-gel glasses have been analyzed during the densification process and compared according to the presence or not of aluminum as a codoping ion. A transition temperature from hydrated to dehydroxyled environments has been found different for doped and codoped samples. However, only slight modifications have been displayed from luminescence measurements beyond this transition. To support the experimental analysis, molecular dynamics simulations have been performed to model the doped and codoped glass structures. Despite no evidence of rare earth clustering reduction due to aluminum has been found, the modeled structures have shown that the luminescent ions are mainly located in aluminum-rich domains. The synthesis of both experimental and numerical analyses has lead us to interpret the aluminum effect as responsible for differences in structure of the luminescent sites rather than for an effective dispersion of the rare earth ions. (C) 2004 Elsevier B.V. All rights reserved.

Two-wavelength whole-field interferometry setup for thermal lens study

In this paper we present a new approach for thermal lens analysis using a two-wavelength DSPI (Digital Speckle Pattern Interferometry) setup for wavefront sensing. The employed geometry enables the sensor to detect wavefronts with small phase differences and inherent aberrations found in induced lenses. The wavefronts was reconstructed by four-stepping fringe evaluation and branch-cut unwrapping from fringes formed onto a diffusive glass. Real-time single-exposure contour interferograms could be obtained in order to get discernible and low-spacial frequency contour fringes and obtain low-noise measurements. In our experiments we studied the thermal lens effect in a 4% Er-doped CaO-Al2O3 glass sample. The diode lasers were tuned to have a contour interval of around 120 ��m. The incident pump power was longitudinally and collinearly oriented with the probe beams. Each interferogram described a spherical-like wavefront. Using the ABCD matrix formalism we obtained the induced lens dioptric power from the thermal effect for different values of absorbed pump power. �� 2012 Copyright SPIE.

Estudos de absor����o e emiss��o de UV/Vis em xerog��is de s��lica dopados com cromo obtidos por processo Sol-Gel

Coordena����o de Aperfei��oamento de Pessoal de N��vel Superior (CAPES)

The ceramic artifacts in archaeological black earth (terra preta) from Lower Amazon Region, Brazil: chemistry and geochemical evolution

Neste trabalho realizou-se a caracteriza����o qu��mica de fragmentos de artefatos cer��micos encontrados em s��tios arqueol��gicos com terra preta no Baixo Amazonas (Cachoeira-Porteira, Par��, Brasil), representativos da cultura Konduri (de 900 a 400 anos AP). Esses fragmentos s��o constitu��dos de SiO₂, Al₂O₃, Fe₂O₃, Na₂O e P₂O₅, sendo que SiO₂ e Al₂O₃, juntos, perfazem mais de 80 % em peso. Os teores de P₂O,₅ s��o relativamente elevados (2,37 % em m��dia) sob a forma de (Al,Fe)-fosfatos, incomuns em cer��micas vermelhas primitivas, mas encontrados em algumas cer��micas arqueol��gicas eg��pcias e romanas. As concentra����es dos elementos tra��os s��o compar��veis ou mesmo inferiores ao n��vel crustal, embora a composi����o total seja pr��xima a mesma. A composi����o qu��mica (exceto P₂O₅) em conjunto com os dados mineral��gicos e texturais indicam material saprol��tico derivado de rochas ��gneas f��lsicas ou rochas sedimentares como mat��ria-prima das cer��micas. Os teores de K, Ca e Na mostram que os feldspatos e fragmentos de rochas foram adicionados ao material argiloso, como sugerido pela mineralogia. Os altos teores de s��lica respondem pela presen��a de cauixi, cariap�� e/ou areias quartzosas. F��sforo deve ter sido incorporado�� matriz argilosa da cer��mica, quando do cozimento de alimentos nos vasos cer��micos, e ainda, em parte, durante a forma����o do perfil de solo tipo ABE sobre Latossolos Amarelos. A mat��ria prima e os temperos (cauixi, cariap��, rochas trituradas e fragmentos de vasos cer��micos descartados) encontram-se dispon��veis pr��ximos aos s��tios at�� a atualidade, e, portanto foram a ��rea fonte dos mesmos para a confec����o dos artefatos cer��micos.

Photoluminescence from germanate glasses containing silicon nanocrystals and erbium ions

We report the first observation of photoluminescence enhancement in Er3+ doped GeO2-Bi2O3 glasses containing silicon nanocrystals (Si-NCs) excited by a laser operating at 980 nm. The growth of approximate to 200% in the intensity of the Er3+ transition S-4(3/2) -&gt; I-4(15/2) (545 nm) and of approximate to 100% for transitions H-2(11/2) -&gt; I-4(15/2) (525 nm), F-4(9/2) -&gt; I-4(15/2) (660 nm), and I-4(5/2) -&gt; I-4(13/2) (1530 nm) was observed in comparison with a reference sample that does not contain Si-NCs. The results open a new road for obtaining efficient Stokes and anti-Stokes emissions in germanate composites doped with rare-earth ions.