Synthesis, characterization, structural refinement and optical absorption behavior of PbWO(4) powders

The present paper describes the synthesis, characterization, structural refinement and optical absorption behavior of lead tungstate (PbWO(4)) powders obtained by the complex polymerization method heat treated at different temperatures for 2h in air atmosphere. PbWO(4) powders were characterized by X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) spectroscopy and ultraviolet visible (UV-vis) absorption spectroscopy measurements. XRD, Rietveld refinement and FT-Raman revealed that PbWO(4) powders are free of secondary phases and crystallizes in a tetragonal structure. The UV-vis absorption spectroscopy measurements suggest the presence of intermediary energy levels into the band gap of structurally disordered powders. (C) 2008 Elsevier B.V. All rights reserved.

Electronic structure, growth mechanism and photoluminescence of CaWO4 crystals

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

Feasibility of internal standardization in the direct and simultaneous determination of As, Cu and Pb in sugar-cane spirits by graphite furnace atomic absorption spectrometry

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

Evaluation and Application of TS-FF-AAS System Using Ceramic Tube as Atomization Cell for Tin Determination in Canned Foods

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

Simultaneous and Direct Determination of As, Bi, Pb, Sb, and Se and Co, Cr, Cu, Fe, and Mn in Milk by Electrothermal Atomic Absorption Spectrometry

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

Simultaneous Determination of Two Groups of Elements in Milk by Electrothermal Atomic Absorption Spectrometry: Evaluation of Ruthenium Modifiers

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

Pump excited state absorption in holmium-doped fluoride glass

The primary excited state absorption processes relating to the (5)I(6) -> (5)I(7) 3 mu m laser transition in singly Ho(3+)-doped fluoride glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the (5)I(6) and (5)I(7) energy levels established the occurrence of two excited state absorption transitions from these energy levels that compete with previously described energy transfer upconversion processes. The (5)I(7) -> (5)I(4) excited state absorption transition has peak cross sections at 1216 nm (sigma(esa)=2.8x10(-21) cm(2)), 1174 nm (sigma(esa)=1x10(-21) cm(2)), and 1134 nm (sigma(esa)=7.4x10(-22) cm(2)) which have a strong overlap with the (5)I(8) -> (5)I(6) ground state absorption. on the other hand, it was established that the excited state absorption transition (5)I(6) -> (5)S(2) had a weak overlap with ground state absorption. Using numerical solution of the rate equations, we show that Ho(3+)-doped fluoride fiber lasers employing pumping at 1100 nm rely on excited state absorption from the lowest excited state of Ho(3+) to maintain a population inversion and that energy transfer upconversion processes compete detrimentally with the excited state absorption processes in concentrated Ho(3+)-doped fluoride glass. (c) 2008 American Institute of Physics.

Foam nest in Scinax rizibilis (Amphibia: Anura: Hylidae)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Vegetable-origin foam employed in dye extraction in tanning and leather processing facilities

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

On Ti-18Si-6B and Ti-7.5Si-22.5B powder alloys prepared by high-energy ball milling and sintering

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

Flow cell within an LED: a proposal for an optical absorption detector

Droplets formed at the tip of a tube under the same conditions possess extreme uniformity of form, volume and weight. These properties of liquid drop formation have been known for a long time and consequently many applications for the drop have been found in instrumentation and chemical analysis methods. In the present paper, we report on the analytical use of a dynamic LED-based flow-through optical absorption detector with optical path length controlled by continuous dropping of a solution. This arrangement consists of a flow cell built within a high-intensity red LED (lambda (max)=630 nm). The feasibility of the detector is demonstrated by colorimetric determination of methylene blue, and ammonium by Berthelot's reaction, in a flow-injection system. For ammonium, the reaction forms a blue dye (indophenol) with a maximum absorption at 630-650 nm. The detection limit, considered as 3 times the signal of the blank, is better than 125 mu g l(-1). The small flow cell represents a good combination of optical path length, low volume and fast washout. This detector can be used advantageously in automated methods and can represent a solution to problems of optical detection involving gas bubbles and precipitation of particles in turbidimetric applications.

Time dependence and energy-transfer mechanisms in Tm3+Ho3+ and Tm3+-Ho3+ co-doped alkali niobium tellurite glasses sensitized by Yb3+

Glass samples with the composition (mol%) 80TeO(2)-10Nb(2)O(5)-5K(2)O-5Li(2)O, stable against crystallization, were prepared containing Yb3+, Tm3+ and Ho3+. The energy transfer and energy back transfer mechanisms in samples containing 5% Yb3+-5% Tm3+ and 5% Yb3+-5% Tm3+-0.5% Ho3+ were estimated by measuring the absorption and fluorescence spectra together with the time dependence of the Yb3+ F-2(5/2) excited state. A good fit for the luminescence time evolution was obtained with the Yokota-Tanimoto's diffusion-limited model. The up-conversion fluorescence was also studied in 5% Yb-5% Tm. 5% Yb-0.5% Ho and 5% Yb-5% Tm-0.5% Ho tellurite glasses under laser excitation at 975 nm. Strong emission was observed from (1)G(4) and F-3(2) Tm3+ energy levels in all samples. The S-5(2) Ho3+ emission was observed only in Yb3+Ho3+ samples being completely quenched in Yb3+/Tm3+/Tm3+ samples. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Evaluation and application of bismuth as an internal standard for the determination of lead in wines by simultaneous electrothermal atomic absorption spectrometry

A method for the direct determination of Pb in wines by simultaneous multi-element atomic absorption spectrometry (SIMAAS) using a transversely heated graphite atomizer, Zeeman-effect background corrector and internal standardization is proposed. Bismuth was used as an internal standard and Pd(NO3)(2) plus Mg(NO3)(2) as chemical modifier,to stabilize both the analyte and the internal standard. The implementation of two pyrolysis steps avoided any build-up of carbonaceous residues on the graphite platform. All diluted samples (1 + 1 v/v) in 0.2% v/v HNO3 and reference solutions (5.0-50 mug l(-1) Ph in 0.2% v/v HNO3) were spiked with 25 mug l(-1) Bi. For a 20 mul aliquot dispensed into the graphite tube, a good correlation (r = 0.9997) was obtained between the ratio of the analyte signal to the internal standard signal and the analyte concentration of the reference solutions. The electrothermal behaviour of Pb and Bi in red, white and rose wines were compared. In addition, absorbance variations due to changes in experimental conditions, such as atomizer temperature, integration time, injected sample volume, radiation beam intensity, graphite tube surface, dilution and sample composition, were minimized by using Bi as internal standard. Relative standard deviations of measurements based on integrated absorbance varied from 0.1 to 3.4% and from 0.5 to 7.3% (n = 12) with and without internal standard correction, respectively. Good recoveries (91-104%) for Pb spikes were obtained. The characteristic mass was 45 pg Pb and the limit of detection based on integrated absorbance was 0.9 mug l(-1) Pb. Internal standardization increased the lifetime of the tube by 25%. Direct determinations of Pb in wines with and without internal standardization approaches were in agreement at the 95% confidence level. The repeatability and the tube lifetime were improved when using Bi as internal standard. The improvement in accuracy using an internal standard was only observed when the analytical results were affected by errors.

Ytterbium-induced energy-transfer upconversion enhancement in Nd3+/Pr3+-codoped PbGeO3-PbF2-CdF2 glass excited at 810nm

The effect of ytterbium ions upon energy transfer (ET) excited upconversion emission in Nd3+/Pr3+ -codoped PbGeO3-PbF2-CdF2 glass under 810 nm diode laser excitation is investigated. The results revealed that the presence of Yb3+ ions in the Nd3+/Pr3+-doped sample yields a fourfold enhancement in the visible and near infrared upconversion luminescence. The dependence of the upconversion process upon the excitation power, Nd3+, and Yb3+ concentrations is examined. The results indicated that ytterbium plays a major role in the ET upconversion process by bridging the 810nm neodymium excitation to praseodymium ions. The population of the Pr3+ ions P-3(0) emitting level was accomplished through a multi-ion interaction involving ground-state and excited-state absorption of pump photons at 810 nm by the Nd3+ followed by successive ET involving the Nd3+-Yb3+ and Yb3+-Pr3+ pairs. There is also direct ET Nd3+-Pr3+. (c) 2005 Elsevier B.V. All rights reserved.

Tungsten permanent chemical modifier with co-injection of Pd(NO3)(2)+Mg(NO3)(2) for direct determination of Pb in vinegar by graphite furnace atomic absorption spectrometry

A tungsten carbide coating on the integrated platform of a transversely heated graphite atomizer (THGA((R))) used together with Pd(NO3)(2) + Mg(NO3)(2) as modifier is proposed for the direct determination of lead in vinegar by graphite furnace atomic absorption spectrometry. The optimized heating program (temperature, ramp time, hold time) of atomizer involved drying stage (110 degrees C, 5 s, 30 s; 130 degrees C, 5 s, 30 s), pyrolysis stage (1000 degrees C, 15 s, 30 s), atomization stage (1800 degrees C, 0 s, 5 s) and clean-out stage (2450 degrees C, I s, 3 s). For 10 mu L of vinegar delivered into the atomizer and calibration using working standard solutions (2.5-20.0 mu g L-1 Pb) in 0.2% (v/v) HNO3, analytical curve with good linear correlation (r = 0.9992) was established. The characteristic mass was 40 pg Pb and the lifetime of the tube was around 730 firings. The limit of detection (LOD) was 0.4 mu g L-1 and the relative standard deviations (n = 12) were typically <8% for a sample containing 25 pg L-1 Pb. Accuracy of the proposed method was checked after direct analysis of 23 vinegar samples. A paired t-test showed that results were in agreement at 95% confidence level with those obtained for acid-digested vinegar samples. The Pb levels varied from 2.8 to 32.4 pg L-1. Accuracy was also checked by means of addition/recovery tests and recovered values varied from 90% to 110%. Additionally, two certified reference materials were analyzed and results were in agreement with certified values at a 95% confidence level. (C) 2006 Elsevier Ltd. All rights reserved.