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Absorption Spectra (absorption + spectrum)
Kinds of Absorption Spectra Selected AbstractsFabrication of Hollow Metal "Nanocaps" and Their Red-Shifted Optical Absorption Spectra,ADVANCED MATERIALS, Issue 10 2005J. Liu Cap-shaped metal nanoparticles (see Figure) have optical spectra with significant absorption in the infrared. Such shapes, produced by physical vapor deposition onto a polymer-particle template, can be readily separated from one another provided that deposition is carried out at an inclination to the plane of the template. The effect of composition, angle of deposition, and thickness on the properties of the cap-shaped particles is discussed. [source] Absorption Spectra of Human Skin In Vivo in the Ultraviolet Wavelength Range Measured by OptoacousticsPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009Merve Meinhardt Knowledge of the optical properties of human skin in the ultraviolet range is fundamental for photobiologic research. However, optical properties of human skin in the ultraviolet spectral range have so far mainly been measured ex vivo. We have determined the absorption spectra of human skin in vivo in the wavelength range from 290 to 341 nm in 3 nm steps using laser optoacoustics. In this technique, optical properties are derived from the pressure profile generated by absorbed light energy in the sample. In a study on 20 subjects belonging to phototypes I,IV, we studied the optical properties at the volar and dorsal aspect of the forearm as well as on the thenar. Analysis of the measured absorption spectra shows that comparable skin areas,like different sides of the forearm,have qualitatively similar optical characteristics. Still, the optical properties may vary substantially within the same area, probably due to the skin structure and inhomogeneities. Comparison of the spectra from different skin sites indicates that the spectral characteristics of the stratum corneum and its chromophores play an important role for the optical properties of human skin in vivo in the ultraviolet B range. [source] Ultraviolet Absorption Spectra of Substituted Phenols: A Computational Study,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2006Lei Zhang ABSTRACT Vertical excitation energies for electronic transitions from the ground state to the first two excited states of phenol, mono- and disubstituted methoxyphenols and methyl-substituted phenols have been characterized with the Time-Dependent Density Functional Theory (TD-DFT), the Complete Active Space Self-Consistent Field method (CASSCF) and the Coupled Cluster with Single and Double Excitations Equation-of-Motion approach (CCSD-EOM) to simulate and interpret experimental ultraviolet absorption spectra. While CASSCF excitation energies for the first two transitions either are grossly overestimated or exhibit a weak correlation with experimental data, both TD-DFT and CCSD-EOM perform very well, reproducing the spectral shifts of both the primary band and secondary band observed upon substitution. The conformational dependence of the calculated excitation energies is generally smaller than the shifts caused by substitution. [source] Magnetic Circular Dichroism and Absorption Spectra of Phosphinidene in Noble-Gas MatricesCHEMINFORM, Issue 17 2005Jeremy J. Harrison Abstract For Abstract see ChemInform Abstract in Full Text. [source] Syntheses, Structures, Magnetic Properties, and X-Ray Absorption Spectra of Carnotite-Type Uranyl Chromium(V) Oxides: A[(UO2)2Cr2O8] (H2O)n (A: K2, Rb2, Cs2, Mg; n = 0, 4).CHEMINFORM, Issue 26 2004A. J. Locock Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Electronic Absorption Spectra of Closed and Open-Shell Tetrathiafulvalenes: The First Time-Dependent Density-Functional Study.CHEMINFORM, Issue 51 2001Raquel Andreu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Synthesis, Structure, and UV,VIS Absorption Spectra of Azo Dyes Derived from (Dialkylamino)thiazole Dimers.CHEMINFORM, Issue 25 2001Jae Joon Kim Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Application of the Perimeter Model to the Assignment of the Electronic Absorption Spectra of Gold(III) Hexaphyrins with [4n+2] and [4n] ,-Electron SystemsCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009Atsuya Muranaka Dr. Abstract Expanded porphyrins: The electronic excited states of two forms of meso -hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1), such as that depicted, have been investigated by density functional calculations and magnetic circular dichroism spectroscopy to assign their low-energy excited singlet states. The electronic excited states of two forms of meso -hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1) have been investigated by density functional calculations and magnetic circular dichroism (MCD) spectroscopy, in order to assign their low-energy excited singlet states. We found that the perimeter model can be successfully applied to the interpretation of the electronic states. In the case of the neutral forms (Au2 -N, Au-N), the absorption bands observed in the NIR and visible region can be assigned to ,,,* transitions referred to as the L and B bands, respectively, analogous to the Q and Soret bands of regular porphyrins. In marked contrast with the neutral forms, the absorption bands of the reduced forms (Au2 -R and Au-R) are attributed to ,,,* transitions involving six frontier molecular , orbitals. By applying the 4N -electron perimeter model, the six orbitals are labeled as h,, h+, s,, s+, l,, and l+, while the observed absorption bands can be assigned to the S, N1, N2, P1, and P2 transitions, in order of increasing energy. [source] Ultraviolet Absorption Spectrum of Chlorine Peroxide, ClOOCl.CHEMINFORM, Issue 33 2007Francis D. Pope Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Crystal growth, optical and luminescence properties of (Ce,Sr)-doped PrAlO3 single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007A. Novoselov Abstract Using the micro-pulling-down method, (Ce,Sr)-doped PrAlO3 square-shaped single crystals (4×4×12 mm) were grown. Structural parameters studied by X-ray powder diffraction were consistent with R3m space group. Compositional homogeneity was checked with electron probe micro-analysis and found quite uniform. Absorption spectra and luminescence characteristics under UV and X-ray excitations were measured at room temperature with no Ce-related emission appeared. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal growth and scintillating properties of (Pr,Si)-doped YAlO3CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007M. Zhuravleva Abstract This paper deals with Pr-doped and Pr, Si-codoped YAlO3 single crystal growth by the micro-pulling-down method and investigation of their spectroscopic and scintillating properties. The Pr3+ 5d -4f radioluminescence intensity is more than 10 times higher than that of Bi4Ge3O12 standard sample, but the Si-codoping decreases it. Absorption spectra of as-grown and air-annealed Si,Pr-codoped YAlO3 samples show along with an onset of 4f -5d transition round 230 nm the induced absorption band at 400 nm which possibly related to a hole center absorption (Pr4+ or O - ). Thermoluminescence measurements above the room temperature were performed in order to monitor deep electron traps. Strong concentration dependence of thermoluminescence was observed for Pr:YAlO3 glow curves. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Studies on Nickel(II) Complexes with Amide-Based Ligands: Syntheses, Structures, Electrochemistry and Oxidation ChemistryEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2008Jyoti Singh Abstract The present work discusses the nickel chemistry in a set of amide-based open-chain ligands with subtle differences in the backbone or terminal amine substituents. The ligands coordinate to the Ni2+ ion through the Namide and Namine atoms maintaining a square-planar geometry. Absorption spectra and NMR studies reveal that the solid-state square-planar geometry is retained in solution. The electrochemical results suggest that the NiIII/NiII redox couple primarily depends on the N4 donors, which is composed of two Namide and twoNamine atoms and not on the peripheral substituents. All four ligands with variable backbone and substituents are equally competent in stabilizing the NiIII state. On the basis of electrochemical findings, chemical oxidations were carried out, and they reveal generation of the NiIII state in two cases, whereas decomposition was observed in others. Preliminary alkene epoxidation reactions suggest that the present nickel complexes transiently stabilize the higher oxidation state of the nickel ion that possibly participates in the oxidation of the substrates.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] [Re6Q7O(3,5-Me2PzH)6]Br2·3,5-Me2PzH (Q = S, Se) , New Octahedral Rhenium Cluster Complexes with Organic Ligands: Original Synthetic Approach and Unexpected Ligand Exchange in the Cluster CoreEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2005Yuri V. Mironov Abstract Two new octahedral rhenium cluster complexes, [Re6S7O(3,5-Me2PzH)6]Br2·3,5-Me2PzH (1) and [Re6Se7O(3,5-Me2PzH)6]Br2·3,5-Me2PzH (2), with the organic ligand 3,5-dimethylpyrazole (3,5-Me2PzH), have been synthesised by reaction of rhenium chalcobromides Cs3[Re6(µ3 -Q7Br)Br6] (Q = S, Se) with molten dimethylpyrazole. During the reaction, all six apical bromine ligands of the cluster complexes are substituted by the organic ligand, which is coordinated through the aromatic nitrogen atom N2. Additionally, the inner ligand µ3 -Br in the cluster core [Re6(µ3 -Q7Br)]3+ is substituted by oxygen, giving cluster cores [Re6(µ3 -Q7O)]2+ with mixed chalcogen/oxygen ligands. Compounds 1 and 2 have been characterised by single-crystal X-ray diffraction analysis. They are isostructural and crystallise with four formula units in the unit cell. Absorption spectra and luminescence characteristics of these two cluster compounds have been investigated in methanol. Absorption starts below 400 nm. For both compounds, broad emissions were found. The fluorescence decays of the two compounds follow a diexponential decay behaviour. The main fluorescence intensity decays have longer fluorescence lifetimes of 3.07 ± 0.03 (1) and 3.96 ± 0.02 µs (2). Studying the thermal stability of both compounds in vacuo showed that the release of 3,5-dimethylpyrazole ligands begins near 200 °C, and decomposition, with the removal of 7 molecules of 3,5-Me2PzH, is complete at 330 °C. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Absorption spectra of recently synthesised organic dyes: A TD-DFT studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2010Denis Jacquemin Abstract We use a time-dependent density functional theory approach to investigate the absorption spectra of a panel of organic dyes synthesised and characterised during 2009. Several chemical modifications (solid-state packing, oxidation, variation of acidity,) are tackled, and both successes and failures of theory are highlighted and discussed. The obtained deviations are compared to the errors reported previously for traditional families of organic dyes. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Reionization bias in high-redshift quasar near-zonesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008J. Stuart B. Wyithe ABSTRACT Absorption spectra of high-redshift quasars exhibit an increasingly thick Ly, forest, suggesting that the fraction of neutral hydrogen in the intergalactic medium (IGM) is increasing towards z, 6. However, the interpretation of these spectra is complicated by the fact that the Ly, optical depth is already large for neutral hydrogen fractions in excess of 10,4, and also because quasars are expected to reside in dense regions of the IGM. We present a model for the evolution of the ionization state of the IGM which is applicable to the dense, biased regions around high-redshift quasars as well as more typical regions in the IGM. We employ a cold dark matter based model in which the ionizing photons for reionization are produced by star formation in dark matter haloes spanning a wide range of masses, combined with numerical radiative transfer simulations which model the resulting opacity distribution in quasar absorption spectra. With an appropriate choice for the parameter which controls the star formation efficiency, our model is able to simultaneously reproduce the observed Ly, forest opacity at 4 < z < 6, the ionizing photon mean-free-path at z, 4 and the rapid evolution of highly ionized near-zone sizes around high-redshift quasars at 5.8 < z < 6.4. In our model, reionization extends over a wide redshift range, starting at z, 10 and completing as H ii regions overlap at z, 6,7. We find that within 5 physical Mpc of a high-redshift quasar, the evolution of the ionization state of the IGM precedes that in more typical regions by around 0.3 redshift units. More importantly, when combined with the rapid increase in the ionizing photon mean-free-path expected shortly after overlap, this offset results in an ionizing background near the quasar which exceeds the value in the rest of the IGM by a factor of ,2,3. We further find that in the post-overlap phase of reionization the size of the observed quasar near-zones is not directly sensitive to the neutral hydrogen fraction of the IGM. Instead, these sizes probe the level of the background ionization rate and the temperature of the surrounding IGM. The observed rapid evolution of the quasar near-zone sizes at 5.8 < z < 6.4 can thus be explained by the rapid evolution of the ionizing background, which in our model is caused by the completion of overlap at the end of reionization by 6 ,z, 7. [source] Effect of Two Different UVA Doses on the Rabbit Cornea and LensPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2009ejka, estmír The aim of the present paper was to examine the irradiation effect of two doses of UVA rays (365 nm) on the rabbit cornea and lens. Corneas of anesthetized adult albino rabbits were irradiated with UVA rays for 5 days (daily dose 1.01 J cm,2 in one group of rabbits and daily dose 2.02 J cm,2 in the second group of animals). The third day after the last irradiation, the rabbits were killed, and their eyes were employed for spectrophotometrical, biochemical and immunohistochemical investigations. Normal eyes served as controls. Absorption spectra of the whole corneal centers were recorded over the UV,VIS (visible) spectral range. Levels of antioxidant and prooxidant enzymes, nitric oxide synthases and nitric oxide (indirectly measured as nitrate concentration) were investigated in the cornea. Malondialdehyde, a byproduct of lipid peroxidation, was examined in the cornea and lens. The results show that the staining for endothelial nitric oxide synthase was more pronounced in corneas irradiated with the higher UVA dose. Otherwise, UVA rays at either dose did not significantly change corneal light absorption properties and did not cause statistically significant metabolic changes in the cornea or lens. In conclusion, UVA rays at the employed doses did not evoke harmful effects in the cornea or lens. [source] Fluorescence Resonance Energy Transfer Between Polyphenolic Compounds and Riboflavin Indicates a Possible Accessory Photoreceptor Function for Some Polyphenolic CompoundsPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2006Kumar Chandrakuntal ABSTRACT The photoreceptive extreme tip of the wheat coleoptile exhibits intense green-yellow fluorescence under UV light, suggesting the presence of UV-absorbing materials. Fluorescence spectra of the intact coleoptile tip and tip homogenate showed the presence of the known photoreceptor pigments flavin and carotene, and a preponderance of phenolic compounds. Absorption spectra and fluorescence spectra of various phenolic compounds showed close overlap with the absorption and fluorescence spectra of the wheat coleoptile tip homogenate. Fluorescence spectra of several phenolic compounds showed close overlap with the absorption bands of flavin, carotene and pterine, suggesting possible energy transduction from phenols to these photoreceptors. Excitation of gentisic acid and ferulic acid with 340 nm light in the presence of flavin showed enhancement of flavin fluorescence in a concentration- and viscosity-dependent fashion, indicating fluorescence resonance energy transfer between them and riboflavin. Furthermore, several phenolic compounds tested generated superoxide anion on excitation at 340 nm, suggesting that superoxide-dependent signal cascades could operate in a polyphenol-mediated pathway. Phenolic compounds thus may act as accessory photoreceptors bringing about excitation energy transfer to the reactive photoreceptor molecules, or they may take over the function of the normal photoreceptor in genetic mutations lacking the system, or both processes may occur. The responses of plants to UV-B and UV-A light in mutants may be explained in terms of various phenolics acting as energy transducers in photoreceptor functioning. [source] Spectroscopy of single-walled carbon nanotubes in aqueous surfactant dispersionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009Dania Movia Abstract Optical studies of single-walled carbon nanotubes (SWNTs) dispersed in aqueous surfactant suspensions have made significant progress since the discovery of their bright band-gap fluorescence in the near-infrared region [M. J. O'Connell et al., Science 297, 593,596 (2002)]. In this article we report the systematic investigation of the effect of chemical purification and oxidation on the spectroscopic properties of SWNTs. The SWNTs samples we prepared differ for the percentage of impurities present, the amount of defects introduced in their graphitic structure and/or the functional groups expressed on their surface. The generation of carboxylic groups on the nanotubes surface by oxidative treatment was validated by means of thermal gravimetric analysis and ATR/Fourier transform IR spectroscopies, as well as Raman spectroscopy. We have solubilized pristine, purified SWNTs (p-SWNTs) and oxidized SWNTs (o-SWNTS) in Milli-Q water using sodium dodecylbenzene sulphonate (SDBS). While our Vis-NIR Absorption spectra of p-SWNTs and o-SWNTS dispersions in aqueous SDBS solution show the loss of the resolution of the characteristic van Hove singularities, NIR Photoluminescence spectra are characterized by structured emission peaks. [source] Indirect absorption edge of TlGaSe2 crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2006Vytautas Grivickas Abstract Absorption spectra of high-quality layered TlGaSe2 single crystals were measured in a wide temperature range. Results obtained at low temperatures show that the direct excitonic absorption initiating at EGdir = 2.127 eV is perturbed by several series of step-like features inherent for the indirect type transitions. Spectral modelling of these features revealed that: (i) the ground state of indirect exciton, n = 1, has a large Rydberg energy of about 100 meV, and (ii) the enhanced absorption to excited indirect excitonic states, n = 2, 3, exceeds the classical prediction for scaling factors K1ind/n3. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Novel Zinc Porphyrin Sensitizers for Dye-Sensitized Solar Cells: Synthesis and Spectral, Electrochemical, and Photovoltaic PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009Cheng-Wei Lee Abstract Novel meso - or ,-derivatized porphyrins with a carboxyl group have been designed and synthesized for use as sensitizers in dye-sensitized solar cells (DSSCs). The position and nature of a bridge connecting the porphyrin ring and carboxylic acid group show significant influences on the spectral, electrochemical, and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins with a phenylethynyl bridge show that both Soret and Q,bands are red-shifted with respect to those of porphyrin 6. This phenomenon is more pronounced for porphyrins 3 and 4, which have a ,-conjugated electron-donating group at the meso position opposite the anchoring group. Upon introduction of an ethynylene group at the meso position, the potential at the first oxidation alters only slightly whereas that for the first reduction is significantly shifted to the positive, thus indicating a decreased HOMO,LUMO gap. Quantum-chemical (DFT) results support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino-substituted porphyrin 5, which exhibits the best photovoltaic performance among all the porphyrins under investigation. From a comparison of the cell performance based on the same TiO2 films, the devices made of porphyrin 5 coadsorbed with chenodeoxycholic acid (CDCA) on TiO2 in ratios [5]/[CDCA]=1:1 and 1:2 have efficiencies of power conversion similar to that of an N3 -based DSSC, which makes this green dye a promising candidate for colorful DSSC applications. [source] Deformed Phthalocyanines: Synthesis and Characterization of Zinc Phthalocyanines Bearing Phenyl Substituents at the 1-, 4-, 8-, 11-, 15-, 18-, 22-, and/or 25-PositionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2005Takamitsu Fukuda Dr. Abstract The synthesis of a series of zinc phthalocyanines partially phenyl-substituted at the 1-, 4-, 8-, 11-, 15-, 18-, 22-, and/or 25-positions (the so-called ,-positions) is reported. Macrocycle formation based on 3,6-diphenylphthalonitrile, o -phthalonitrile, and zinc acetate predominantly yielded the near-planar disubstituted complex and opposite tetrasubstituted isomer, while the lithium method yielded the sterically hindered hexasubstituted complex and adjacent tetrasubstituted isomer. All compounds have been characterized by 1H NMR, MALDI-TOF-MS, and elemental analysis methods. In addition, crystal structures have been solved for the di-, hexa-, and octasubstituted complexes and the adjacent tetrasubstituted isomer. DFT geometry optimization calculations predict more highly deformed structures than those observed in the crystals. The packing force of the crystals cannot therefore be ignored, particularly for the less phenyl-substituted derivatives. The crystal structures have revealed that overlap of the phenyl groups causes substantial deformation of the phthalocyanine (Pc) ligands within the crystals, while strong ,,, stacking in the remainder of the Pc moiety lacking phenyl substituents can suppress the impact of the deformation. Absorption spectra show sizable red shifts of the Q-band with increasing number of phenyl groups. Analysis of the results of absorption spectra and electrochemical measurements reveals that a substantial portion of the red shift is attributable to the ring deformations. Molecular orbital calculations lend further support to this conclusion. A moderately intense absorption band emerging at around 430 nm for highly deformed octaphenyl-substituted zinc Pc can be assigned to the HOMO,LUMO+3 transition, which is parity-forbidden for planar Pcs, but becomes allowed since the ring deformations remove the center of symmetry. [source] Effect of reduction/oxidation treatment on blue photorefraction in In:Fe:Cu:LiNbO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2010Suhua Luo Abstract In:Fe:Cu:LiNbO3 crystals with reduced/oxidized treatments were prepared by the Czochralski method. The defect structure was analyzed by the UV-Visible absorption spectra. The blue photorefractive properties, such as the refractive index change, response time, recording sensitivity, dynamic range as well as two-wave coupling gain coefficient, were also investigated at 488 nm wavelength using the two-wave coupling experiment. Comparing the as-grown and oxidized In:Fe:Cu:LiNbO3 crystals, the reduced sample has the highest recording sensitivity and largest dynamic range. Meanwhile, the high diffraction efficiency is still maintained. Experimental results definitely show that reduction treatment is an effective method to improve the blue photorefractive performance of In:Fe:Cu:LiNbO3 crystals. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Defect structure and spectroscopic characteristics of codoped Hf: Er: LiNbO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2009Liang Sun Abstract Codoped Hf: Er: LiNbO3 crystals have been grown by the Czochralski technique. Defect structures of the crystals were analyzed by IR absorption spectra, and the compositions of the crystals were measured by X-ray fluorescent spectrograph. A new OH, -associated vibrational peak at 3492 cm,1 was revealed in 6 mol % Hf: 1 mol % Er: LiNbO3 crystal. It was attributed to (HfNb), -OH, -(ErNb)2, defect centers. The Er3+ concentrations in crystals gradually decreased with the increase of the codoped Hf4+ concentrations in the melts. The emission characteristics of the crystals were investigated by the fluorescence spectrum. It was found that the luminescent intensity in codoped 6 mol % Hf: 1 mol % Er: LiNbO3 crystal was 3.5 times stronger than that in single doped 1 mol % Er: LiNbO3 crystal. The luminescent enhancement effect was successfully explained on the basis of defect structure of the crystals. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth, etching morphology and spectra of LiAlO2 crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2008Taohua Huang Abstract ,-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×103 cm,2. The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical investigations on the existence of phase transition in ZnO:Li thin films prepared by DC sputtering methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2008A. Abu EL-Fadl Abstract We investigated the effect of temperature on the absorption spectra of Zn0.8Li0.2O thin films (ZnO:Li), deposited at 573 K, in the wavelength range 190-800 nm. The films were deposited on sapphire, MgO or quartz substrates by DC sputtering method. The results show a shift of the optical energy gap (Eg), with direct allowed transition type near the fundamental edge, to lower wavelengths as the temperature increases. The temperature rate of Eg changes considerably showing an anomaly around 320 K depending on type of substrate. The founded results indicated that replacement of Zn ions with Li ions induces a ferroelectric phase in the ZnO wurtzite-type semiconductor. The exponential dependence of the absorption coefficient on the incident photon energy suggests the validity of the Urbach rule. (© 2007 WILEY -VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Increased optical damage resistance of Zr:LiNbO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2007Liang Sun Abstract Zr: LiNbO3 crystals has been grown. The crystal composition and phase are analyzed by X-ray diffration. The optical damage resistance ability of Zr: LiNbO3 crystals is studied by the Sénarmont compensation method and the transmitted beam pattern distortion method. The saturated value of the birefringence change of 6 mol% Zr: LiNbO3 crystal is 1.01×10 -4, which is seven times smaller than that of congruent pure LiNbO3 crystal. The results of UV-Visible and IR absorption spectra of Zr: LiNbO3 crystals powerfully confirm that the optical damage resistance threshold concentration of the Zr4+ ions doped in LiNbO3 crystals is about 6 mol% in the melt. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photostimulated changes of properties of CdTe filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2007T. D. Dzhafarov Abstract The effect of illumination during the close-spaced sublimation (CSS) growth on composition, structural, electrical, optical and photovoltaic properties of CdTe films and CdTe/CdS solar cells were investigated. Data on comparative study by using X-ray diffraction (XRD), scanning electron microscopy (SEM), absorption spectra and conductivity-temperature measurements of CdTe films prepared by CSS method in dark (CSSD) and under illumination (CSSI) were presented. It is shown that the growth rate and the grain size of CdTe films grown under illumination is higher (by factor about of 1.5 and 3 respectively) than those for films prepared without illumination. The energy band gap of CdTe films fabricated by both technology, determined from absorption spectra, is same (about of 1.50 eV), however conductivity of the CdTe films produced by CSSI is considerably greater (by factor of 107) than that of films prepared by CSSD. The photovoltaic parameters of pCdTe/nCdS solar cells fabricated by photostimulated CSSI technology (Jsc = 28 mA/cm2, Voc =0.63 V) are considerably larger than those for cells prepared by CSSD method (Jsc = 22 mA/cm2, Voc = 0.52 V). A mechanism of photostimulated changes of properties of CdTe films and improvement of photovoltaic parameters of CdTe/CdS solar cells is suggested. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and photorefractive properties of Mg:Ce:Cu:LiNbO3 crystals grown by Czochralski methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2006Y. X. Fan Abstract In this paper, photorefractive properties of Mg:Ce:Cu:LiNbO3 crystals were studied. The crystals doped with different concentration of Mg ions have been grown by the Czochralski method. Mg concentrations in grown crystals were analyzed by an inductively coupled plasma optical emission spectrometry (ICP-OE/MS). The crystal structures were analyzed by the X-ray powder diffraction (XRD), ultraviolet-visible (UV-Vis) absorption spectra and infrared (IR) transmitatance spectra. The photorefractive properties of crystals were experimentally studied by using two-beam coupling. In this experiment we determined the writing time, maximum diffraction efficiency and the erasure time of crystals samples with He-Ne laser. The results showed that the dynamic range (M/#), sensitivity (S) and diffraction efficiency (,) were dependent on the Mg doping concentration, and the Mg(4.58mol%):Ce:Cu:LiNbO3 crystal was the most proper holographic recording media material among the six crystals studied in the paper. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and optical damage resistance of Sc, Er Co-doped LiNbO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2005X. H. Zhen Abstract A series of Sc:Er:LiNbO3 crystals have been grown by Czochralski method. Their ultraviolet-visible (UV-Vis) absorption spectra was measured and discussed to investigate their defect structure. The optical damage resistance of Sc:Er:LiNbO3 crystals was characterized by the transmitted beam pattern distortion method. It increases remarkably when the concentration of Sc2O3 exceeds a threshold concentration. The optical damage resistance of Sc (3.0mol %):Er:LiNbO3 is much higher than that of the Er:LiNbO3. The intrinsic and extrinsic defects were discussed to explain the enhance of the optical damage resistance in the Sc:Er:LiNbO3 crystals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Simultaneous determination of metronidazole and spiramycin in bulk powder and in tablets using different spectrophotometric techniquesDRUG TESTING AND ANALYSIS, Issue 1 2010Fatma I. Khattab Abstract Metronidazole (MZ) is an anti-infective drug used in the treatment of anaerobic bacterial and protozoa infections in humans. It is also used as a vetinary antiparasitic drug. Spiramycin (SP) is a medium-spectrum antibiotic with high effectiveness against Gram-positive bacteria. Three simple, sensitive, selective and precise spectrophotometric methods were developed and validated for the simultaneous determination of MZ and SP in their pure form and in pharmaceutical formulations. In methods A and B, MZ was determined by the application of direct spectrophotometry and by measuring its zero-order (D0) absorption spectra at its ,max = 311 nm. In method A, SP was determined by the application of first derivative spectrophotometry (D1) and by measuring the amplitude at 218.3 nm. In method B, the first derivative of the ratio spectra (DD1) was applied, and SP was determined by measuring the peak amplitude at 245.6 nm. Method C entailed mean centring of the ratio spectra (MCR), which allows the determination of both MZ and SP. The methods developed were used for the determination of MZ and SP over a concentration range of 5,25 µg ml,1. The proposed methods were used to determine both drugs in their pure, powdered forms with mean percentage recoveries of 100.16 ± 0.73 for MZ in methods A and B, 101.10 ± 0.90 in method C, 100.09 ± 0.70, 100.02 ± 0.88 and 100.49 ± 1.26 for SP in methods A, B and C, respectively. The proposed methods were proved using laboratory-prepared mixtures of the two drugs and were successfully applied to the analysis of MZ and SP in tablet formulation without any interference from each other or from the excipients. The results obtained by applying the proposed methods were compared statistically with a reported HPLC method and no significant difference was observed between these methods regarding both accuracy and precision. Copyright © 2010 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||