Fission-track dating of South American natural glasses: an overview

Although many glass-bearing horizons can be found in South American volcanic complexes or sedimentary series, only a relatively few tephra and obsidian-bearing volcanic fields have been studied using the fission-track (FT) dating method. Among them, the volcanics located in the Sierra de Guamani (east of Quito, Ecuador) were studied by several authors. Based upon their ages, obsidians group into three clusters: (1) very young obsidians, similar to 0.2Ma old, (2) intermediate-age obsidians, similar to 0.4- similar to 0.8 Ma old, and (3) older obsidians, similar to 1.4- similar to 1.6 Ma old. The FT method is also an efficient alternative technique for identification of the sources of prehistoric obsidian artefacts. Provenance studies carried out in South America have shown that the Sierra de Guamani obsidian occurrences were important sources of raw material for toot making during pre-Columbian times. Glasses originated from these sources were identified in sites distributed over relatively wide areas of Ecuador and Colombia.Only a few systematic studies on obsidians in other sectors were carried out. Nevertheless, very singular glasses have been recognised in South America, such as Macusanite (Peru) and obsidian Quiron (Argentina), which are being proposed as additional reference materials for FT dating. Analyses of tephra beds interstratified with sedimentary deposits revealed the performance of FT dating in tephrochronological studies. A remarkable example is the famous deposit outcropping at Farola Monte Hermoso, near Bahia Blanca (Buenos Aires Province), described for the first time by the middle of the 19th century by Charles Darwin.Considering the large number of volcanic glasses that were recognised in volcanic complexes and in sedimentary series, South America is a very promising region for the application of FT dating. The examples given above show that this technique may yield important results in different disciplinary fields. (c) 2005 Elsevier Ltd. All rights reserved.

Determining the interfacial density of states in metal-insulator-semiconductor devices based on poly(3-hexylthiophene)

Low frequency admittance measurements are used to determine the density of interface states in metal-insulator-semiconductor diodes based on the unintentionally doped, p-type semiconductor poly(3-hexylthiophene). After vacuum annealing at 90 degrees C, interface hole trapping states are shown to be distributed in energy with their density decreasing approximately linearly from similar to 20x10(10) to 5x10(10) cm(-2) eV(-1) over an energy range extending from 0.05 to 0.25 eV above the bulk Fermi level. (c) 2008 American Institute of Physics.

Thermo and photochromic properties of Na2O-WO3-SbPO4 glasses

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

DSC studies on crystallization mechanisms of tellurite glasses

The purpose of this work is to study the 20Li(2)O-80TeO(2) glass using the differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques in order to understand the crystallization kinetics on this glass matrix. To study the glass by DSC, screened samples with different particle sizes to resolve the observed asymmetrical crystallization peak were used. DSC curves for particles smaller than 38 mum in size show two distinct crystallization peaks, associated to distinct phase transformation in this glass, leading to activation energies at 301 and 488 kJ mol(-1). XRD analysis reveals that the first crystallization peak is attributed to TeO2 crystalline phase while the second one to the alpha-TeO3 and an unidentified phase.(C) 2004 Elsevier B.V. All rights reserved.

Multicolor up conversion emission and color tunability in Yb3+/Tm3+/Ho3+ triply doped heavy metal oxide glasses

Multicolor and white light emissions have been achieved in Yb3+, Tm3+ and Ho3+ triply doped heavy metal oxide glasses upon laser excitation at 980 nm. The red (660 nm), green (547 nm) and blue (478 nm) up conversion emissions of the rare earth (RE) ions triply doped TeO2-GeO2-Bi2O3-K2O glass (TGBK) have been investigated as a function of the RE concentration and excitation power of the 980 nm laser diode. The most appropriate combination of RE in the TGBK glass host (1.6 wt% Yb2O3, 0.6 wt% Tm2O3 and 0.1 wt% Ho2O3) has been determined with the purpose to tune the primary colors (RGB) respective emissions and generate white light emission by varying the pump power. The involved infrared to visible up conversion mechanisms mainly consist in a three-photon blue up conversion of Tm3+ ions and a two-photon green and red up conversions of Ho3+ ions. The resulting multicolor emissions have been described according to the CIE-1931 standards. (C) 2011 Elsevier B.V. All rights reserved.

Spectroscopic studies on glassy Ni(II) and Co(II) polyphosphate coacervates

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

Crystallization study of molybdate phosphate glasses by thermal analysis

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

Local order around rare earth ions during the devitrification of oxyfluoride glasses

Erbium L-3-edge extended x-ray absorption fine structure (EXAFS) measurements were performed on rare earth doped fluorosilicate and fluoroborate glasses and glass ceramics. The well known nucleating effects of erbium ions for the crystallization of cubic lead fluoride (based on x-ray diffraction measurements) and the fact that the rare earth ions are present in the crystalline phase (as indicated by Er3+ emission spectra) seem in contradiction with the present EXAFS analysis, which indicates a lack of medium range structural ordering around the Er3+ ions and suggests that the lead fluoride crystallization does not occur in the nearest neighbor distance of the rare earth ion. Molecular dynamics simulations of the devitrification process of a lead fluoride glass doped with Er3+ ions were performed, and results indicate that Er3+ ions lower the devitrification temperature of PbF2, in good agreement with the experimental results. The genuine role of Er3+ ions in the devitrification process of PbF2 has been investigated. Although Er3+ ions could indeed act as seeds for crystallization, as experiments suggest, molecular dynamics simulation results corroborate the experimental EXAFS observation that the devitrification does not occur at its nearest neighbor distance. (c) 2008 American Institute of Physics.

Zootherapy goes to town: the use of animal-based remedies in urban areas of NE and N Brazil

This paper examines the therapeutic possibilities offered by animal-based remedies in five Brazilian cities. Information was obtained through semi-structured questionnaires applied to 79 traders of medicinal animals at Sao Luis, Teresina, Joao Pessoa and Campina Grande (Northeastern) and Belem (Northern) Brazil. We recorded the use of 97 animal species as medicines, whose products were recommended for the treatment of 82 illnesses. The most frequently quoted treatments concerned the respiratory system (58 species; 407 use-citations), the osteomuscular system and conjunctive tissue (46 species; 384 use-citations), and the circulatory system (34 species; 124 use-citations). Mammals (27 species), followed by reptiles (24) and fishes (16) represented the bulk of medicinal species. In relation to users, 53% of the interviewees informed that zootherapeuticals resources were sought after by people from all social classes, while 47% stated that low income people were the main buyers. The notable use and commercialization of medicinal animals to alleviate and cure health problems and ailments in cities highlights the resilience of that resource in the folk medicine. Most remedies quoted by interviewees depend on wild-caught animals, including some species under official protection. Among other aspects, the harvesting of threatened species confers zootherapy a role in the discussions about biodiversity conservation in Brazil. (C) 2007 Elsevier B.V.. All rights reserved.

Reversible holographic glasses using visible lasers

Antimony based glasses have been investigated for the first time regarding the possibility of holographic data storage using visible lasers sources. Changes in both refractive index and the absorption coefficient were measured using a holographic setup. The modulation of the optical constants is reversible by heat treatment. Bragg gratings were written under visible light of an Ar laser and erased thermally.

Twentyfold blue upconversion emission enhancement through thermal effects in Pr3+/Yb3+-codoped fluoroindate glasses excited at 1.064 mu m

Infrared-to-visible upconversion emission enhancement through thermal effects in Yb3+-sensitized Pr3+-doped fluoroindate glasses excited at 1.064 mu m is investigated. A twentyfold increase in the 485 nm blue emission intensity as the sample temperature was varied from 20 to 260 degrees C was observed. The visible upconversion fluorescence enhancement is ascribed to the temperature dependent multiphonon-assisted anti-Stokes excitation of the ytterbium sensitizer and excited-state absorption of the praseodymium acceptor. A model based upon conventional rate equations considering a temperature dependent effective absorption cross section for the F-2(7/2)-->F-2(5/2) transition of the Yb3+ and (1)G(4)-->P-3(0) excited-state absorption of the Pr3+, agrees very well with the experimental results. (C) 2000 American Institute of Physics. [S0021-8979(00)08209-8].

Antimony orthophosphate glasses with large nonlinear refractive indices, low two-photon absorption coefficients, and ultrafast response

Antimony glasses based on the composition Sb2O3-SbPO4 were prepared and characterized. The samples present high refractive index, good transmission from 380 to 2000 nm, and high thermal stability. The nonlinear refractive index, n(2), of the samples was studied using the optical Kerr shutter technique at 800 nm. The third-order correlation signals between pump and probe pulses indicate ultrafast response (<100 fs) for all compositions. Enhancement of n(2) was observed by adding lead oxide to the Sb2O3-SbPO4 composition. Large values of n(2)approximate to10(-14) cm(2)/W and negligible two-photon absorption coefficients (smaller than 0.01 cm/GW) were determined for all samples. The glass compositions studied present appropriate figure-of-merit for all-optical switching applications. (C) 2005 American Institute of Physics.

Raman investigation of structural photoinduced irreversible changes of Ga10Ge25S65 chalcogenide glasses

The influence of time exposure, when exposed to above band gap light (3,52 eV) and annealing, on Ga10Ge25S65 glasses has been studied through their effects on the structure and optical properties. To evaluate the photostructural change infrared and Raman spectra for bulk Ga10Ge25S65 glasses have been measured before and after exposure. The Raman spectra are interpreted in terms of models in which the Ge atoms are fourfold coordinated and the S atoms are two fold coordinated. The observed changes in the spectral region of (S-S) stretching vibration (470-490 cm (-1)) is a direct evidence for the occurrence of important structural changes in local bonding configuration caused by optical irradiation. It is shown that the dominant photostrucural changes are chain formation tendency of the chalcogenide atoms under the laser irradiation rather than rings.

Lead-cadmium oxyfluoride glasses and glass-ceramics

Glasses and glass-ceramics have been obtained in oxyfluoride systems involving lead and cadmium fluorides and one of the well-known glass former oxides SiO2, B2O3 and TeO2. Vitreous domains were established and a wide range of compositions including high heavy metal contents lead to stable glasses. Amorphous structures have been studied by short-range order spectroscopy techniques (Raman scattering and x-ray absorption) and molecular basic structures have been identified. Besides the usual oxides, the role of glass former could also be proposed for cadmium ions. Special attention has been paid for crystallization process. Cubic lead fluoride, cubic lead tellurite, tetragonal tellurium oxide and a solid solution of the type Pb1-xCdxF2 are obtained as crystallization products depending on the composition and temperature of heat treatments. Pb1-xCdxF2 solid solutions are well known superionic materials and obtaining this solid solution as a crystal phase could be very interesting for applications concerning ionic electrical conduction properties. The addition of rare earth ions led to the control of the crystallization process. In the presence of the nucleating ion only the cubic form beta-PbF2 was identified. Rare earth ions are present in the crystal phase and crystal-like spectroscopic properties were observed suggesting interesting applications for these perfectly transparent glass ceramics in photonics.

Electrochemical studies with copper-based alloys: open-circuit potential oscillations in alkaline media

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)