Absorption Edge (absorption + edge)

Distribution by Scientific Domains
Distribution within Physics and Astronomy

Kinds of Absorption Edge

  • k absorption edge


  • Selected Abstracts


    Role of Structural Fe(III) and Iron Oxide Nanophases in Mullite Coloration

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2001
    Amde Djemai
    Six mullite samples, derived from heat-treated natural kaolinites with various iron content, were investigated and compared to synthetic monophasic mullite. They were analyzed by X-ray diffraction, diffuse reflectance spectroscopy, and electron paramagnetic resonance. To quantify mullite coloration, the CIE colorimetric system was used. In contrast to synthetic mullite, samples showed charge transfer bands involving O2, and Fe3+ ions as well as ferric crystal-field transitions due to Fe3+ ions in iron oxide nanoparticles. Absorption edges showed red shifts. The resulting yellowness, saturation of which increased with the content of iron oxide nanoparticles, is direct evidence for the coloring effect of Fe3+ ions. [source]


    Effect of temperature and isomorphic atom substitution on optical absorption edge of TlInS2xSe2(1-x) mixed crystals (0.25 , x , 1)

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2010
    N. M. Gasanly
    Abstract The optical properties of the TlInS2xSe2(1-x)mixed crystals (0.25 , x , 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400,1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS2xSe2(1-x)mixed crystals. The transmission measurements carried out in the temperature range of 10,300 K revealed that the rates of change of the indirect band gaps with temperature are , = ,9.210,4 eV/K, ,6.110,4 eV/K, ,4.710,4 eV/K and ,5.610,4 eV/K for TlInS2, TlInS1.5Se0.5, TlInSSe and TlInS0.5Se1.5 crystals, respectively. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth and characterization of near stoichiometric LiNbO3 single crystal

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2007
    S. H. Yao
    Abstract A near stoichiometric LiNbO3 single crystal has been grown by the Czochralski method from a 58.5% Li melt hold in a large platinum crucible. High resolution X-ray rocking curves of 300 and 0006 reflections indicated that the near stoichiometric LiNbO3 crystal possesses the high structural quality. Compared with the congruent LiNbO3, the near stoichiometric LiNbO3 possesses shorter ultraviolet absorption edge, thus higher Li concentration. The OH, infrared absorption band analyses showed that the Li concentration in the near stoichiometric LiNbO3 crystal is higher than that in the congruent LiNbO3 crystal. This result is in good agreement with that of the ultraviolet absorption edge. The electro-optic (EO) coefficient ,22 of the near stoichiometric LiNbO3 crystal was measured to be 6.75 pm/V higher than that of congruent LiNbO3 crystal. It also proves the near stoichiometric LiNbO3 electro-optic Q-switched requires a low driving voltage and it is advantageous for the device performance. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Inhomogeneity of composition in near-stoichiometric LiNbO3 single crystal grown from Li rich melt

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2006
    L. Gao
    Abstract A near-stoichiometric LiNbO3 single crystal has been grown by the Czochralski technique from a melt of 58.5 mol% Li2O. Its composition homogeneity was assessed by measuring the UV absorption edge. It was found that the maximum composition difference is about 0.03 mol% in the radial direction and 0.05 mol% in the axial direction. Differential scanning calorimetry (DSC) analysis was performed on the powder from the synthesized raw material and the frozen melt after crystal growth. The analytical results indicate that, during crystal growth, the magnitude of lithium volatilization from the melt surface is more than the degree of segregation from the crystal. The volatilized lithium diffuses into the crystal to compensate for the lithium segregation in the LiNbO3 crystal. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Preparation and investigation of (CuInSe2)x(2ZnSe)1-x and (CuInTe2)x(2ZnTe)1-x solid solution crystals

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2004
    I. V. Bodnar
    Abstract The (CuInSe2)x(2ZnSe)1-x and (CuInTe2)x(2ZnTe)1-x solid solution crystals prepared by Bridgman method and chemical vapor transport have been studied. The nature of the crystalline phases, the local structure homogeneity and composition of these materials have been investigated by X-ray diffraction (XRD) and Electron Probe Microanalysis (EPMA) methods. The analysis revealed the presence of chalcopyrite-sphalerite phase transition between 0.6 , X , 0.7. Lattice constants, value of , position parameter and bond length between atoms were also calculated. It was found that the lattice parameters exhibit a linear dependence versus composition. The transmission spectra of solid solution crystals in the region of the main absorption edge were studied. It was established that the optical band gap of these materials changes non-linearly with the X composition. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Nanostructured Titanium Oxynitride Porous Thin Films as Efficient Visible-Active Photocatalysts,

    ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007
    E. Martnez-Ferrero
    Abstract Nanocrystalline mesoporous N-doped titania films have been prepared for the first time. The introduction of nitrogen into the anatase structure starts at 500,C, with N bonding to titanium via oxygen substitution. Increasing the treatment temperature leads to the formation of TiN (TiN1,xOx) and N-doped rutile showing mixed-valence Ti states. Microstructural characterization shows that the ordered mesoporosity is maintained until 700,C, where TiN (TiN1,xOx) begins to form. Optical characterization shows that the discrete introduction of N is able to shift the titania absorption edge. The photocatalytic tests give the best results under visible light excitation for the film nitrided at 500,C. At this temperature the concentration of nitrogen in the structure is optimal since oxygen vacancies are still not important enough to promote the recombination of the photogenerated electrons and holes. [source]


    Structures of Four Crystal Forms of Decaplanin

    HELVETICA CHIMICA ACTA, Issue 5 2003
    Christopher Lehmann
    The glycopeptide antibiotic decaplanin (1; formerly known as MM 47761 and M86-1410) crystallizes in two P21 and two P6122 crystal forms, each with four monomers in the asymmetric unit, with solvent contents varying from 48 to 69%. Although with ca. 600 unique atoms, the structures are larger than typical small molecules, one was solved by direct methods. The other three were solved by typical macromolecular methods: single-wavelength anomalous diffraction (SAD) of the Cl-atoms present naturally in the structure, multiple-wavelength anomalous diffraction (MAD) at the Br absorption edge for a crystal soaked in NaBr solution, and molecular replacement. There is evidence of appreciable radiation damage with loss of 20,30% of the covalent and ionic halogens affecting the synchrotron datasets that may even have unintentionally facilitated the MAD structure solution. The structures contain the dimer units typical of antibiotics related to vancomycin, but, in addition, there are a variety of further intermolecular interactions responsible for the polymorphy leading to intertwined 61 -helices in two of the crystal forms. Except for the sugars and some sidechains, the conformations of the 16 independent monomers are very similar. [source]


    Silicon-Based Near-Visible Logpile Photonic Crystal

    ADVANCED MATERIALS, Issue 37 2010
    Ganapathi Subramania
    A nanocavity structure is embedded inside a silicon logpile photonic crystal that demonstrates tunable absorption behavior at near visible wavelengths well beyond the absorption edge of silicon. This is due to silicon's indirect bandgap resulting in a relatively slow increase in the absorption of silicon with decreasing wavelength. Our results open up the possibility of utilizing the wide, complete three dimensional photonic gap enabled by the large refractive index of silicon to create three dimensional photonic crystal based devices well into the visible regime. [source]


    Precursory microstructures in Zr,Cu,Al,Ni bulk metallic glasses examined by anomalous small-angle scattering at the Zr K edge

    JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007
    Isao Murase
    Anomalous small-angle X-ray scattering measurements of Zr,Cu,Al,Ni quaternary alloys have been made at the Zr K absorption edge. In melt-quenched samples, small cluster components without crystallization were found. The contrast change at the edge suggested that compositional fluctuation of Al is incorporated. [source]


    Poly(triarylamine): Its synthesis, properties, and blend with polyfluorene for white-light electroluminescence

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2007
    Hung-Yi Lin
    Abstract A new high-molecular-weight poly(triarylamine), poly[di(1-naphthyl)-4-anisylamine] (PDNAA), was successfully synthesized by oxidative coupling polymerization from di(1-naphthyl)-4-anisylamine (DNAA) with FeCl3 as an oxidant. PDNAA was readily soluble in common organic solvents and could be processed into freestanding films with high thermal decomposition and softening temperatures. Cyclic voltammograms of DNAA and PDNAA exhibited reversible oxidative redox couples at the potentials of 0.85 and 0.85 V, respectively, because of the oxidation of the main-chain triarylamine unit. This suggested that PDNAA is a hole-transporting material with an estimated HOMO level of 5.19 eV. The absorption maximum of a PDNAA film appeared at 370 nm, with an estimated band gap of 2.86 eV from the absorption edge. Unusual multiple photoluminescence maxima were observed at 546 nm, and this suggested its potential application in white-light-emission devices. Nearly white-light-emission devices could be obtained with either a bilayer-structure approach {indium tin oxide/poly(ethylenedioxythiophene):poly(styrene sulfonate)/PDNAA/poly[2,7-(9,9-dihexylfluorene)] (PF)/Ca} or a polymer-blend approach (PF/PDNAA = 95:5). The luminance yield and maximum external quantum efficiency of the light-emitting diode with the PF/PDNAA blend as the emissive layer were 1.29 cd/A and 0.71%, respectively, and were significantly higher than those of the homopolymer. This study suggests that the PDNAA is a versatile material for electronic and optoelectronic applications. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1727,1736, 2007 [source]


    Overview and new developments in softer X-ray (2 < , < 5) protein crystallography

    JOURNAL OF SYNCHROTRON RADIATION, Issue 1 2004
    John R. Helliwell
    New methodologies with synchrotron radiation and X-ray free electron lasers (XFELs) in structural biology are being developed. Recent trends in harnessing softer X-rays in protein crystallography for phase determination are described. These include reference to a data-collection test at 2.6 wavelength with a lysozyme crystal on SRS station 7.2 (Helliwell, 1983) and also use of softer X-rays (2, wavelength) to optimise f," at the xenon L1 absorption edge in the Single Isomorphous Replacement Optimised Anomalous Scattering ('SIROAS') structure determination of apocrustacyanin A1 with four, partially occupied, xenon atoms (Cianci et al., 2001; Chayen et al., 2000). The hand of the protein was determined using the f," enhanced sulphur anomalous signal from six disulphides in the protein dimer of 40,kDa. In a follow-up study the single wavelength xenon L1 -edge f," optimised data set alone was used for phase determination and phase improvement by solvent flattening etc. (CCP4 DM) (Olczak et al., 2003). Auto-tracing of the protein was feasible but required additional diffraction data at higher resolution. This latter could be avoided in future by using improved tilted detector settings during use of softer X-rays, i.e. towards back-scattering recording (Helliwell, 2002). The Olczak et al. study has already led to optimisation of the new SRS beamline MPW,MAD,10 (see www.nwsgc.ac.uk) firstly involving the thinning of the beryllium windows as much as possible and planning for a MAR Research tilted detector `desk top beamline' geometry. Thus the use of softer, i.e. 2 to 3, wavelength range, X-rays will allow optimisation of xenon and iodine L -edge f," and enhancing of sulphur f," signals for higher throughput protein crystallography. Softer X-rays utilisation in protein crystallography includes work done on SRS bending-magnet station 7.2 in the early 1980s by the author as station scientist (Helliwell, 1984). In the future development of XFELs these softer X-ray wavelengths could also be harnessed and relax the demands to some extent on the complexity and cost of an XFEL. Thus, by use of say 4, XFEL radiation and use of a back-scattering geometry area detector the single molecule molecular transform could be sampled to a spatial resolution of 2,, sufficient, in principle, for protein model refinement (Miao et al., 1999). Meanwhile, Miao et al. (2003) report the first experimental recording of the diffraction pattern from intact Escherichia coli bacteria using coherent X-rays, with a wavelength of 2,, at a resolution of 30,nm and a real-space image constructed. The new single-particle X-ray diffraction-imaging era has commenced. [source]


    X-ray magnetic circular dichroism imaging with hard X-rays

    JOURNAL OF SYNCHROTRON RADIATION, Issue 3 2001
    K. Sato
    X-ray polarization-contrast images resulting from X-ray magnetic circular dichroism (XMCD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders, and a high-spatial-resolution X-ray charge-coupled-device detector. The sample used was a hexagonal-close-packed cobalt polycrystal foil having a thickness of about 4,m. The X-ray polarization-contrast image resulting from XMCD was observed at a photon energy of 10,eV above the cobalt K -absorption edge (7709,eV). The observed contrast in the image was reversed by inversion of the magnetic field. Furthermore, the contrast was reversed again at a photon energy of 32,eV above the cobalt K -absorption edge. [source]


    Photo-Induced Effect in Heavy Metal Oxide Glasses

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010
    Jong Heo
    Photo-induced phenomena in binary (PbO,Ga2O3) and ternary (PbO,Bi2O3,Ga2O3) heavy metal oxide glasses were investigated. A red shift up to ,0.05 eV in the absorption edge of 75PbO,25Ga2O3 glass (mol%) was observed by illuminating the subbandgap light for 30 min. This shift was completely erased by the heat treatment near the glass transition temperature. Refractive index of the glass at 600 nm also increased ,0.011 by the illumination. It is believed that the presence of lone-pair electrons associated with Pb-polyhedra is essential to realize a reversible photo-induced effect in these oxide glasses. [source]


    Positron Lifetime Study of the Crystal Evolution and Defect Formation Processes in a Scintillating Glass

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009
    Jiaxiang Nie
    The crystal evolution and defect formation in scintillating glasses as a consequence of thermal annealing were studied by annihilation lifetime spectroscopy and UV-Vis absorption spectroscopy. The annihilation lifetime spectra and UV-Vis spectra were recorded on glass 50SiO2,45ZnO,5BaF2 before and after annealing at 580C for 16, 32, and 48 h, respectively. The results show that the three lifetime components (,1, ,2, and ,3) and the corresponding intensities (I1, I2, and I3) change systematically with increasing annealing time. This reflects the crystal evolution and defect formation in the glass matrix. The continued crystal evolution was also revealed by the UV-Vis spectra, as the absorption edge of the material shifted to a lower energy with prolonged annealing. [source]


    Single-Source Sol-Gel Synthesis of Nanocrystalline ZnAl2O4: Structural and Optical Properties

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
    Sanjay Mathur
    Nanometer-sized zinc aluminate (ZnAl2O4) particles were synthesized from heterometal alkoxides, [ZnAl2(OR)8], possessing an ideal cation stoichiometry for the ZnAl2O4 spinel. ZnAl2O4 is formed at 400C, which is the lowest temperature reported for the formation of monophasic ZnAl2O4. 27Al magic-angle spinning nuclear magnetic resonance spectroscopy revealed that ZnAl2O4 possesses an inverse structure at <900C, while the normal spinel phase is observed at higher temperatures. The homogeneity of the in-depth composition and Zn:Al stoichiometry (1:2) was confirmed by electron spectroscopy for chemical analysis. Evaluation of the valence-band spectra of ZnAl2O4 and ZnS suggested that the hybridization of O 2p and Zn 3d orbitals is responsible for lowering the bandgap in the latter. The average crystallite size showed an exponential relationship to the calcination temperature (X-ray diffractometry and transmission electron microscopy data). The optical spectra of different spinel powders (average particle sizes, 20,250 nm) showed that the absorption edge exhibits a blue shift as particle size decreases. [source]


    The study of structural changes of amorphous Ge2Sb2Te5 films after annealing by optical absorption spectroscopy

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010
    Tamihiro Gotoh
    Abstract Optical absorption spectra of post-annealed Ge2Sb2Te5 films were measured in the photon energy range from 0.5 to 3.5,eV. Optical absorption edge and Urbach slope parameter changed slightly with increase in annealing temperature and then abrupt changes occurred at around crystallization temperature. The band gaps of amorphous and cubic Ge2Sb2Te5 are 0.74 and 0.54,eV, respectively. The spectroscopic method is demonstrated to be suitable for evaluation of structural disorder and crystalline composition in phase-change materials. [source]


    Characterization of Fe 3d states in CuFeS2 by resonant X-ray emission spectroscopy

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009
    Katsuaki Sato
    Abstract Resonant X-ray emission spectroscopy (RXES) experiments were carried out in a single crystal of chalcopyrite CuFeS2, an antiferromagnetic semiconductor with a golden lustre, to unravel the overlapping d,d and charge-transfer transitions extending well above the absorption edge, which cannot be observed by conventional optical absorption experiments. The observed RXES spectra have been analyzed by means of cluster-model calculation with configuration interaction, which leads to the conclusion that CuFeS2 is a Haldane,Anderson insulator with a negative value of charge transfer energy, , = ,3 eV. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Observation of interfacial electrostatic field-induced changes in the silicon dielectric function using spectroscopic ellipsometry

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2008
    J. Price
    Abstract This work investigates the capability of spectroscopic ellipsometry to measure charge trapping centers in thin dielectric films. Specific interfacial electrostatic fields, induced by electrons injected into charge trapping states at the interface, have been identified that directly affect the underlying silicon substrate critical points. The effect of a field-induced change in the silicon fundamental absorption edge due to different processing conditions affecting the oxygen vacancy defects at the interface is presented. Measuring the field-induced change in the silicon dielectric function between a sample with a 2 nm HfO2 film as-deposited and the same sample after a 1000 C anneal in an N2 ambient reveals that a stronger interfacial field is present for the as-deposited HfO2 film. These results are consistent with the understanding that high temperature anneals work well to passivate oxygen vacancy defects at the silicon/HfO2 interface. Finally, we compare our results with Second Harmonic Generation where specific resonant features are identifiable with electric field enhancements at the same interface. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Anomalous scattering and isomorphous replacement in X-ray diffuse scattering holography

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2007
    Kopeck
    Abstract Two concepts of X-ray diffuse scattering holography resulting in local atomic structure are presented. The first one uses the anomalous scattering near the absorption edge of a selected element. The second one is based on the variation of atomic scattering factor due to the isomorphous replacement of a selected atom in the structure by another one with different scattering properties. Feasibility of both concepts was demonstrated experimentally on a RbCl single crystal and GaMnAs epitaxial layer. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Blue-shift of absorption edge in LaTiO2N by controlling the anion nonstoichiometry

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006
    Toshihiro Moriga
    Abstract The perovskite-type oxynitride LaTiO2N was prepared by heating an oxide precursor at 950 C for 5 hours under NH3 atmosphere at a flow rate of 1 dm3/min. The precursor was prepared by the polymerized complex method. The oxynitride obtained was almost stoichiometric, LaTi(O0.68N0.32)2.9, with a reddish orange color. The oxynitride was successively annealed at 950 C for 3 hours under a NH3 atmosphere at flow rates of 50 cm3/min, 30 cm3/min and 10 cm3/min, respectively. The color and composition varied from yellow LaTi(O0.89N0.11)2.8 through green-yellow LaTi(O0.93N0.07)2.9 to light-blue LaTi(O0.98N0.02)2.9 in accordance with the decreased flow rate. The absorption edges varied from 2.28 eV for the reddish orange, 2.56 eV for the yellow, 3.17 eV for the green-yellow, to 3.44 eV for the light-blue oxynitrides. Annealing under NH3 is therefore effective in color tuning, mainly resulting in a blue-shift of the absorption edge. DV-X, calculations support the conclusion that the lower flow rate of NH3 led to a lower amount of nitrogen and higher oxygen levels in the oxynitrides. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Stoichiometry effects and the Moss,Burstein effect for InN

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2006
    K. S. A. Butcher
    Abstract We examine the Moss,Burstein effect for InN and demonstrate an independent method for determing its magnitude for high carrier concentration material. Consequently it is shown that the extent of the Moss,Burstein effect is less than 0.72 eV for a high carrier concentration sample with a 1.88 eV absorption edge. Early results are also provided for high band-gap low carrier concentration InN films that can be grown reprodcibly, vindicating the work of early groups in the field. The role of stoichiometry is examined in relation to point defects that appear to be common to many forms of InN. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Valence-band splitting and optical anisotropy of AlN

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2010
    G. Rossbach
    Abstract The dielectric function (DF) of hexagonal AlN on Si(111) is determined in the range between 1 and 9.8,eV by spectroscopic ellipsometry (SE). Due to its large negative crytal-field splitting wurtzite AlN features large dichroism. Showing that SE is sensitive to both components of the DF around the absorption edge, a uniaxial model is applied which yields transition energies for the free excitonic state. The in-plane tensile stress leads to a red-shift of these transitions and to an enlarged splitting. The experimental data are compared to the results of band-structure calculations demonstrating excellent overall agreement. In addition, two high-energy critical points in the ordinary DF were determined at energies of about 7.75 and 8.85,eV. [source]


    Pressure dependence of the optical properties of wurtzite and rock-salt Zn1,xCoxO thin films

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007
    J. A. Sans
    Abstract In this paper we investigate the electronic structure of Zn1,xCoxO by means of optical absorption measurements under pressure. Thin films of Zn1,xCoxO with different Co content (from 1 to 30%) were prepared by pulsed laser deposition on mica substrates. Absorption spectra exhibit three main features that are clearly correlated to the Co content in the films: (i) absorption peaks in the infrared associated to crystal-field-split internal transitions in the Co 3d shell, with very small pressure coefficients due to their atomic character; (ii) a broad absorption band below the fundamental edge associated to charge transfer transitions, that exhibit relatively large pressure coefficients, indicating that the Co 3d final states must be strongly hybridized to the conduction band; and (iii) a blue-shifted fundamental absorption edge associated to band to band transitions with a pressure coefficient close to that of pure ZnO. In the up-stroke the transition pressure from wurtzite to rock-salt phase decrease almost linearly as the Co increases, from 9.5 GPa in pure ZnO to about 6.5 GPa for x = 30%. In the down-stroke pressure we observe a similar behavior, yielding a metastable rock-salt phase at room pressure, after a pressure cycle up to 15 GPa. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Indirect absorption edge of TlGaSe2 crystals

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2006
    Vytautas 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]


    Spin-polarized XANES: theoretical analysis of the Ni K-edge of NiF2

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2005
    G. Smolentsev
    Abstract Theoretical interpretations of spin-dependent X-ray absorption near edge structure (XANES) spectra measured by selectively monitoring of the Ni K-beta emission while scanning the excitation energy through the Ni K absorption edge have been performed. Analysis is based on a combination of self-consistent spin-polarized calculation of muffin-tin potential and a full multiple scattering theory of X-ray absorption. This approach allows us to separate the influence of dipole transition matrix elements and the density of empty electronic states on spin-dependent XANES. It is found that the matrix elements affect splitting between spin-up and spin-down spectra only near the absorption threshold, while differences in densities of states slightly shift the spectra in the region 25,35 eV above the main edge. The effects of the multielectron-term-dependent broadening of spin-dependent XANES and mixing of purely spin-polarized spectra were taken into account. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optically pumped lasing and gain formation properties in blue Inx Ga1,x N MQWs

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004
    K. Kojima
    Abstract Lasing and gain formation properties have been studied in an InxGaN1,x multiple quantum wells lasing at around 460 nm by employing the modified variable stripe length method (VSLM) and pump and probe spectroscopy (P&P). It was found that the spontaneous emission (Esp) appeared far below absorption edge (Ea) that is observed as a photo-bleaching negative-peak in P&P, indicating the formation of localized tail states. Lasing peaks appeared in between Esp and Ea with wide spectral distribution. This is consistent with the results where VSLM revealed the broad feature of optical gain spectra associated with rapid peak saturation of lasing even just above the threshold photo-pumping power density. Such mechanism observed in In-rich InxGa1,xN MQWs is contributed not only from the broad distribution of localized density-of-states but also from hot carrier distribution (determined by Maxwell,Boltzmann statistics), temperature of which is raised up due to long energy relaxation time to localized tail states. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Properties of the fundamental absorption edge of InN crystals investigated by optical reflection and transmission spectra

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004
    Y. Ishitani
    Abstract InN crystals are grown on sapphire substrates using a plasma-assisted MBE system. The carrier concentrations of the samples are 2 1018,1 1019 cm,3. Optical transmission and reflectance measurements are performed on these samples in the temperature range 5,300 K. The resultant spectra are analysed by theoretical spectra based on the LO-phonon,plasmon coupling scheme for the phonon-related factor and non-parabolic conduction band structure for the electronic transition factor. The observed absorption edge is estimated to originate from a valence band to conduction band transition rather than a defect- or impurity-related transition. It is estimated that InN has a bandgap energy in the range 0.59,0.65 eV. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    A new luminescent defect state in low temperature grown amorphous SiNxOy thin films

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010
    Hengping Dong
    Abstract We reported the observation of photoluminescence (PL) from low-temperature grown amorphous silicon oxynitride (a-SiNxOy) films with its peak location tunable in a wide range from 450 to 600 nm by controlling the Si/N ratios. The origin of luminescence from a-SiNxOy film has been thoroughly investigated. From the results of the optical absorbance spectrum, an oxygen-induced new luminescent defect state, which was characterized to be responsible for the light emission, was determined to locate at about 0.65 eV from the absorption edge. The measurements of Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectrum (XPS) has verified the existence of O-Si-N bonding configuration, which serves as this new luminescent defect state in this kind of material ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optical properties of ZnS:Mn nanocrystals

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010
    F. Ahmed
    Abstract The optical properties of Mn-doped zinc sulfide (ZnS) nanocrystals embedded in SiO2 matrix are studied by spectroscopic ellipsometry (SE). The crystals are obtained by sequential multi-energy ion implantation of Zn, S, and Mn into a silica layer grown on Si(111) followed by a subsequent annealing for 30 min at 900 C. The formation of the nanocrystals is evidenced by transmission electron microscopy. The application of a critical-point based model for the analysis of the SE data yields die dielectric function (DF) between 0.6 and 6.5 eV. A pronounced shift of the absorption edge towards higher energies is detected for the nanocrystals In comparison to bulk ZnS ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Carrier-induced refractive index change in InN

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2008
    C. Bulutay
    Abstract Rapid development of InN technology demands comprehensive assessment of the electronic and optoelectronic potential of this material. In this theoretical work the effect of free electrons on the optical properties of the wurtzite phase of InN is investigated. The blue shift of the optical absorption edge by the free-carrier band filling is known as the Burstein-Moss effect for which InN offers to be a very suitable candidate as has been recently demonstrated experimentally. Due to well known Kramers-Kronig relations, a change in absorption is accompanied by a change in the index of refraction. Considering n-type InN samples with free electron concentrations ranging from 51017 to 51020 cm,3, and employing a nonlocal empirical pseudopotential band structure, it is shown that this leads to a few percent change of the index of refraction. These carrier-induced refractive index changes can be utilized in optical switches, futhermore it needs to be taken into account in the design of InN-based optical devices such as lasers and optical modulators. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]