Localized Excitation Model Research Articles

Magnetic field induced absorption in Pb xEu1-xTe magnetic semiconductors

We report an investigation of the optical absorption spectrum, using non-polarized light, in Pb xEu1-xTe, x=0 and x=0.095, epitaxial thick layers grown by molecular beam epitaxy (MBE). The absorption edge is described by a broad band, due to the electronic transitions from the 4f7 of Eu2+ to the states in 4f6 5d configuration, as seen previously in bulk Eu chalcogenides. When a magnetic field is applied, a narrow absorption band (full width ~50 meV) emerges from the broad one. The energy of this absorption peak red shifts when the magnetic field increases, and reaches saturation when the Eu2+ attain ferromagnetic arrangement. This behaviour can be described by a localized excitation model with d - f exchange interaction.

Inductively coupled plasma mass spectrometric study of laser sputtering from the surface of an Al–Cu–Fe alloy and quasicrystal

The fractionation behavior induced by laser desorption and ablation of the Al 70Cu 20Fe 10 intermetallic alloy and of the Al 65Cu 23Fe 12 quasicrystal has been examined in terms of the structural properties of the two compounds. Elemental fractionation during laser desorption and ablation sampling was investigated by using inductively coupled plasma mass spectrometry. The experiments were carried out in two different power density regimes by using a Nd-YAG laser with 266 nm wavelength and single 6 ns laser pulses. In the high power density regime (>0.04–0.07 GW/cm 2) the effect of the laser power density on ablation behavior was similar for the two materials. In the low power density regime (<0.04–0.07 GW/cm 2) large differences have been found between the alloy and the quasicrystal. The results are interpreted on the basis of a thermodynamic vaporization process for the intermetallic alloy. An electronic model of localized excitation is suggested for the physical process of surface material removal from a quasicrystal.

Laser induced desorption and ablation: mechanism of metal removal from an Al‐Cu‐Fe alloy and a quasicrystal of the same composition

Quasicrystals are a special class of metallic alloys that share some of the properties of crystals. Their structures reduce to a single repeating unit like that of the unit cell of a crystal. The quasi‐unitcell is representative of a cluster like structure where electrons cannot move with freedom as in metals. Quasicrystals are formed of metallicelements but they do not have metallic properties.The diversity of the fractionation behavior induced by laser desorption and ablation of the Al70Cu20Fe10 of the intermetallicalloy and of the Al65Cu23Fe12 quasicrystal has been examined in terms of the structural properties of the two compounds. Elemental fractionation during laser desorption and ablation sampling was investigated by using inductively coupled plasma mass spectrometry. The experiments were carried out in two different irradiance regimes by a Nd‐YAG laser with 266 nm wavelength and single 6 nanosecond laser pulses. In the high irradiance regime (&gt;0.04, 0.07GW/cm2) the effect of the laser irradiance is not discriminating. In the low irradiance regime (&lt;0.04, 0.07GW/cm2) large differences have been found between the alloy and the quasicrystal. The results have been interpreted on the basis of a thermodynamic vaporization process for the intermetallic alloy. An electronic model of localized excitation is suggested for the physical process of surface material removal from a quasicrystal.

Electronic Structure of Sodium Nitrate: Investigations of Laser Desorption Mechanisms

This theoretical study uses ab initio quantum mechanical methods to investigate the electronic properties of ground and excited state sodium nitrate. We calculated electronic properties of the crystalline material for bulk, clean, and defected surfaces. The results of these calculations are used to explain the photoexcitation/desorption mechanism and support the conclusions of an earlier experimental investigation of the laser desorption of NO from single-crystal sodium nitrate. Ab initio periodic Hartree−Fock (PHF) theory was used to investigate the “molecular−ionic” character of crystalline sodium nitrate. The calculations indicate that the electronic structure of the bulk and cleavage surface are virtually identical (i.e., no shift in the resonant absorption profile is expected). This finding is consistent with the experimental results on the wavelength dependence of NO desorption yields for crystalline NaNO3. However, changes in the absorption manifold are found to accompany the removal of external nitrate oxygens (producing surface nitrite groups). The presence of these chemical defects causes states to appear in the band gap producing a red shift in the absorption band. Complete active space self-consistent field (CASSCF) calculations on NO3-, NO3, and NO2-, support the “local excitation model” of the π* ← π2 transition. These calculations also indicate that the transition energies of the nitrate ion are unaffected by the presence of the surrounding ions. The photoexcitation/dissociation mechanism of the nitrate ions in the crystal, however, differs from gas-phase processes in that the neutral photodetachment channel, observed in the gas phase, is energetically inaccessible in the solid due to the stabilization of ionic species (relative to neutrals) by the crystalline field.

Off-Normal Incidence Piezoreflectivity of SrF2and BaF2in the Core Exciton Region

Off-normal incidence piezoreflectivities of SrF 2 and BaF 2 in the 4 p and 5 p core exciton regions have been measured. The cubic, tetragonal and trigonal deformation potentials are determined. The results are interpreted by the localized excitation model; signs and magnitudes of the deformation potentials of the core excitons, as well as their energies and intensities. Slater-Condon parameters, and Coulomb and exchange interactions between electrons and holes are reasonably determined.

Piezoreflectivity Spectra under Uniaxial Stressesof Core Excitons in RbCl

Piezoreflectivity spectra of Rb + core excitons in RbCl were measured at liquid N 2 temperature and splitting energies due to uniaxial deformations were obtained. The splitting energies were calculated with the use of the localized excitation model given by Satoko and Sugano. The calculated values were in agreement with experimental results under the trigonal deformation and the localized excitation model was shown to be applicable to the analysis of piezoreflectivity spectra. From the splitting energies determined under the tetragonal deformation, one electron expectation values of potential field energy were obtained. The one electron expectation values were discussed in terms of a point charge model and atomic functions.

A CASSCF description of the nπ * singlet and triplet electronic excited states of the trans-glyoxal molecule

A CASSCF study is presented for the 1,3(n→π *) transitions of the trans-glyoxal molecule, based on a localized excitation model suggested by Iwata. It is shown that with a proper choice of the active space and the correct balance between intra- and intermoiety excitations, simple wavefunctions can produce results comparable to the ones obtained by large CI calculations, and in good agreement with experiment.

Excited-state properties of a (2,2'-bipyridine)ruthenium(II) complex, [Ru(CN)4(bpy)]2-, a model of localized excitation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExcited-state properties of a (2,2'-bipyridine)ruthenium(II) complex, [Ru(CN)4(bpy)]2-, a model of localized excitationMasako Kato, Seigo Yamauchi, and Noboru HirotaCite this: J. Phys. Chem. 1989, 93, 9, 3422–3425Publication Date (Print):May 1, 1989Publication History Published online1 May 2002Published inissue 1 May 1989https://doi.org/10.1021/j100346a010RIGHTS & PERMISSIONSArticle Views254Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (515 KB) Get e-Alerts

Energy transfer between J-aggregated dye monolayers

Energy transfer between two Langmuir-Blodgett films has been measured for the first time under conditions where both layers of dye are highly concentrated and J aggregated. The distance dependence of energy transfer was examined by the technique of interposing of a varying number of fatty acid layers between the dye layers. The efficiency of energy transfer was found to decrease with the fourth power of the distance. This is the behavior expected when the donor excitation is localized. For extensively delocalized excitation a quadratic dependence has been predicted. The strong resonance coupling between donor and acceptor in the present case results in efficient energy transfer over distances that are comparable with the expected delocalization of excitation in the donor aggregate so that the localized excitation model is appropriate. A three-dye system of J-aggregated dyes is also described. The efficiency of energy transfer from initial donor to ultimate acceptor is on the order of 90% over about 100 Å.

Piezoreflectivity Studies of Rb+4pCore Excitons in RbBr

Measurements were made to obtain piezoreflectivity spectra of Rb + core excitons in RbBr under a stress along the [011] direction at room temperature. From the dichroism of the spectra, trigonal deformation potentials of structures located at 16.1, 16.5, 17.0, 17.4 and 18.2 eV are determined to be -0.17, -0.48, -0.57, -0.09 and 0.34 eV, respectively. Those deformation potentials are in good agreement with values calculated from the localized excitation model for the core excitons proposed by Satoko and Sugano. It is concluded, therefore, that the excitons located at 16.1and 18.2 eV are mainly of the (4 p ) 5 (5 s ) and (4 p ) 5 (4 d γ) characters, respectively, and that the localized excitation model is useful in the analysis of the core excitons.

Piezoreflectance of Rubidium Chloride in the Vacuum Ultraviolet Region from 6 to 30 eV

Piezoreflectance spectra of rubidium chloride were measured in the photon energy range from 6 to 30 eV at about 120 K. For the structure at 9.01 eV, cubic piezoreflectivity spectrum do not have line shape proportional to that of the logarithmic energy derivative of reflectivity spectrum, and both of tetragonal and trigonal responses on piezoreflectivity were observed. We ascribed it to a composite of the L and X excitons. The piezoreflectance responses of the core excitons located between 15 and 18.5 eV are interpreted well by the localized excitation model by Satoko and Sugano.

Resonant photoemission and Ta 5p core reflectance spectra of 1T- and 2H-TaSe 2

Reflectance spectra of 2H- and 1T-TaSe 2 have been measured at room temperature in the region between 20 and 60 eV. The multiplet structures in the Ta 5p core excitation region are analyzed on the localized excitation model. The ultraviolet photoemission spectra have revealed a resonant enhancement of the Ta 5d and Se 4p valence bands for the excitation of the Ta 5p core states. The difference of the multiplet structures as well as of the resonant behavior between 1T- and 2H-polytypes has elucidated the hybridization of the Se 4p states with the Ta 5d states in the valence bands of TaSe 2.

Final State Interactions of Inner Core Absorption Excitation in Transition Metal Halides

Absorption spectra resulting from the inner 3p-shell excitation of transition metal ions in halide compounds are measured in the photon energy range from 25 to 140 eV with synchrotron radiation from SOR-RING. The observed characteristic multiplet structures spreading over 10–20 eV are well explained by the localized excitation model for the 3p 5 3d m+1 excited states, providing the evaluation of the final state interactions. The asymmetry of the absorption bands of the transition metal compounds with more than half-filled 3d-shell is interpreted as due to the interference caused by the super Coster-Kronig transition, in contrast to the rather symmetric and broad spectral line shape in the compounds with less than half-filled 3d-shell.

Localized excitations and the geometry of the n.pi.* excited states of pyrazine

Previous theoretical work has shown that the lowest excited singlet state of pyrazine, the ..pi..* /sup 1/B/sub 3/u state, is best described in terms of interacting excitations localized on each nitrogen. The present work refines the localized excitation model and considers its implications for the geometry of the /sup 1/B/sub 3/u state. Hartree-Fock calculations show that the best single configuration description of the n..pi..* state has broken (/sup 1/B/sub 1/) symmetry with the excitation strongly localized at one end of the molcule. If the symmetry-restricted hf result is used for reference, this localization describes an important correlation effect. The excited-state geometry was probed using configuration interaction wave functions based on the symmetry-restricted orbitals, as well as properly symmetrized ''valance-bond'' wave functions based on the broken symmetry solutions. Both descriptions lead to a very flat potential for a b/sub 1u/ vibrational mode. This mode reduces the molecular geometry from D/sub 2h/ to C/sub 2v/. We present spectroscopic evidence of our own and of other workers which is consistent with such a flat potential.

The structure and motion of the self-interstitial in diamond

We have made self-consistent semi-empirical molecular orbital calculations for various possible self-interstitial geometries in diamond, both with and without lattice distortion. Total energies are obtained, not merely the sum of one-electron eigenvalues. The results show that the (100) split interstitial has the lowest formation energy, not the cubic, hexagonal or bond-centred forms favour previously.The nature of the interstitial does not support the local heating model of enhanced diffusion in the presence of recombination or ionisation. A Bourgoin-Corbett mechanism involving negative hexagonal and neutral split interstitials is possible, but the apparent stability of the negative hexagonal interstitial may be an artefact of the calculation. We suggest a local excitation model is appropriate in fourfold-coordinated semiconductors.

Absorption spectra of excitons in alkali-halides in the vacuum-ultra-violet region

On the basis of the localized excitation model, the spectra of K + - 3 p electron excitation in potassium halides are studied theoretically by using methods of the ligand field theory and a good agreement with the experiment is obtained. Some discussions are given on the applicability of the Frenkel exciton model to the VUV spectra of other alkali halides.

Scaling behaviour of charged-prong multiplicity distributions in high-energy hadronic collisions and local excitation model

Scaling behaviour of charged-prong multiplicity distributions in high-energy hadronic collisions and local excitation model

Absorption Spectra of Excitons in Alkali Halides in the Vacuum-Ultraviolet Region

On the basis of the localized excitation model, characteristic absorption spectra of excitons in alkali halides in the range of photon energy around 20 eV corresponding to the n p 6 → n p 5 n ' s and n p 6 → n p 5 n d excitations of alkali ions are theoretically treated by using methods developed in the ligand field theory. By assuming reasonable values of Slater integrals, the spin-orbit interaction constant and the ligand-field strength, the observed positions including their chemical shifts and the relative intensities of five absorption peaks called A , B , C , D and E in RbX(X=F, Cl, Br, I) are explained satisfactorily. In constant to the case of the band picture, the excited d -orbital responsible for the absorption of RbX is shown to be mainly of the d γ character, although mixing of the p 5 s , p 5 d e and p 5 d γ configurations is appreciable.