bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical properties of transition metal impurities in CdSe II. Photoionization spectra
Authors: Raranowski J. M. , Langer J. M. 
Published: July 2007

AbstractThe photoionization absorption spectra of Cr and Fe impurities in CdSe are presented. They are very well described in terms of photo‐transitions from the localized 3d shell to the conduction band. The ionization energies and the matrix elements of electric dipole transitions are determined. It is found that deep donor levels of Cr2+ and Fe2+ arc 0.62 and 0.63 eV above the top of the valence band, respectively and are temperature‐indepenent. Observed spectra of CdSe:Fe2+ are succesfully correlated with previously published results of photosensitive EPR of CdSe:Fe3+. The photoionization processes for other transition metal impurities are discussed. The ionization energies for some of them are estimated.
Raman scattering intensity of polaritons for general wave vectors. II. Experimental investigations in BeSO4·H2O
Authors: Unger B. 
Published: July 2007

AbstractThe theory presented in Part I [1] for the Raman scattering efficiency of polaritons in uniaxial piezoelectric crystals is used to interpret experiments on the dependence of the scattered intensities on the direction of the polariton wave vector kp. The measurements have been performed with BeSO4 · 4 H2O in the v3‐region of the SO ions at 1100 cm−1 for the limit (kp ≫ ωp/c). kp is rotated in the (x, y) and (x, z) planes, and a good agreement between theory and experiment is obtained. The contributions of the defromation potential and the macroscopic electric field to the scattering efficiency are determined in relative units as a function of the direction of k.
Raman‐ and infrared measurements and the study of phase transitions in DyVO4
Authors: D'Ambrogio F. , Brüesch P. , Kalbfleisch H. 
Published: July 2007

AbstractThe observed Raman and infrared active lattice vibrations of DyVO4 are calculated using a valence force field for the internal vibrations of the VO4 complexes and a central force field for the external vibrations. On this basis the degree of coupling between internal and external lattice modes is calculated and found to be small for most of the modes. In addition, the frequencies for the low temperature orthorhombic structure below 13.8 K are calculated by adopting a slightly modified force field with the appropriate symmetry. The effect of such an orthorhombic deformation is very small for the non‐degenerate frequencies but yields splittings of the degenerate frequencies of the order of 10 cm−1. These predictions are in agreement with the observations.
Chaleur spécifique et propriétés magnétiques de I'oxysulfure d'ytterbium
Authors: Rossat‐Mignod J. , Quezel G. , Berton A. , Chaussy J. 
Published: July 2007

AbstractL'étude de la susceptibilité magnétique de monocristaux d'Yb2O2S et les mesures de chaleur spécifique à basse température ont montré que le niveau fondamental de l'ion Yb3+ est un doublet isolé et peu anisotrope. Les processus d'aimantation ont été étudiés par des expériences de diffraction neutronique sous champ et par des mesures d'aimantation jusqu'à 80 kOe. De l'ensemble de ces résultats nous avons déterminé le champ cristallin agissant sur l'ion Yb3+ et estimé l'ordre de grandeur des interactions magnétiques.
Resolution of apparent APW–OPW energy band differences in NaCl
Authors: Melvin J. S. , Smith T. 
Published: July 2007

AbstractThe electron energy bands in NaCl have been calculated by the augmented plane wave (APW) method. Substantial agreement is obtained with earlier orthogonalized plane wave and empirical pseudopotential calculations. There are large differences from two earlier APW calculations in which, it is suggested, numerical problems may have been present.
Impurity spin states in the paramagnetic phase of ferromagnets
Authors: Timmesfeld K. H. 
Published: July 2007

AbstractA theory has been developed for impurity spins in a Heisenberg ferromagnet in the temperature range above Tc for which numerical calculations have been performed using as a simple model a simple cubic crystal with nearest‐neighbour exchange constant and a defect spin with different spin and nearest‐neighbour exchange values. The calculations show that there exist in certain cases resonances and localized spin states for the impurity spin the intensity of which goes to zero with increasing temperature. Since no coupling between the normal modes of the spin system has been included, the width of those states is nearly unchanged with temperature.
Far infrared reflectivity of Cdas2
Authors: Gregora I. , Petzelt J. 
Published: July 2007

AbstractFar infrared reflectivity of Cdas2 bulk crystals in polarized light has been measured at room and liquid‐nitrogen temperature in the 30 to 400 cm−1 frequency range. It is shown that the model of classical non‐interacting oscillators represents the experimental curves adequately. The results are in agreement with the group‐theoretical analysis of the zonecentre lattice modes. Parameters of the best‐fit oscillators, longitudinal‐mode frequencies, and real and imaginary parts of the corresponding dielectric‐function tensor are given. The influence of the free‐carrier effects on the optical properties investigated is shown to be negligible.
On the properties of the KDP type ferroelectrics with impurities
Authors: Stamenković S. , Zeković S. 
Published: July 2007

AbstractThe properties of KDP type ferroelectrics with impurities (D in KH2PO4 and H in KD2PO4) are considered using the method of zero‐temperature Green function. The linewidth of the polarization waves caused by their scattering on such impurities as well as the local frequency of impurity itself are calculated. The obtained results can be tested by measuring an intensity of the coherent (for H in KD2PO4) or incoherent (for D in KH2PO4) inelastic scattering respectively of slow neutrons scattered by such impure ferroelectrics.
Spin relaxation of conduction electrons in highly doped semiconductors (InSb, Si, Ge)
Authors: Gershenzon E. M. , Pevin N. M. , Fogelson M. S. 
Published: July 2007

AbstractExperimental data of the temperature and concentration dependence of the ESR line‐width in highly doped n‐InSb, Ge: As, and Si: P are compared with theoretical calculations. For the spin–phonon interaction the temperature dependence and the values of the constants obtained agree within one or two orders of magnitude with theoretical results. Only qualitative agreement has been obtained for the contribution of relaxation by ionized impurity scattering. Possible sources of the line‐broadening are discussed in the limit of low temperatures, where the linewidth does not depend on temperature.
The magnetic scattering of neutral particles in polar media and the study of the permittivity dispersion in space and time
Authors: Dogonadze R. R. , Kornyshev A. A. 
Published: July 2007

AbstractThe scattering of a compound particle by a bound system in the case of weak interaction is considered. The Born cross‐sections for positronium and muonium scattering by a polar nonmagnetic medium were expressed by the complex permittivity function εαß(q, ω). The possibility of an experimental study of the frequency and wave vector dependence of the permittivity of homogeneous isotropic media using data on the scattering of leptonic atoms with spin transitions is investigated. The determination of Im {1/ε∥(q, ω)} by small‐angle thermal scattering data is also discussed.
Electron–phonon interaction in tellurium
Authors: Braune W. , Herrmann Karin , Herrmann R. 
Published: July 2007

AbstractIn the present work two temperature dependent microwave absorption lines (I and II) in tellurium are investigated for the case (1 ≧ h ω/kBT ≧ 0.4). The semiclassical formalism for piezoelectric electron‐phonon cyclotronresonance [1] describes the temperature behaviour of the absorption line II. The ttemperature dependence of the amplitude of line I permits the interpretation as an absorption of an impurity level of about 0.3 meV above the valence band.
Resonance Raman scattering in III–V semiconductors and their alloys
Authors: Renucci M. A. , Renucci J. B. , Cardona M. 
Published: July 2007

AbstractThe resonances in the Raman cross section of InAs and several pseudobinary alloys of III–V compounds in the neighbourhood of the E0 and E1 gaps were investigated. The alloying technique was used to bring the gaps to the region where the lines of the Ar‐ion laser occur. The E0‐Raman resonance shifts with temperature the same as the corresponding absorption gap, while a much smaller shift is exhibited by the E1 resonance. These resonant gaps shift with alloy concentration less than the corresponding absorption gaps, a fact which seems to be a reflection of the more localized nature of the Raman scattering phenomenon. The LO phonon exhibits in the forbidden scattering configurations a strong resonance near E1 at 77 °K. This resonance disappears rapidly as the temperature is increased.
Interionic potentials in liquid alkali metals
Authors: Waseda Y. , Suzuki K. 
Published: July 2007

AbstractThe Born‐Green equation has been analyzed numerically to derive the effective interionic potentials from the observed structural data for liquid alkali metals (Li, Na, K, Rb, Cs) using a linearized simultaneous equation method. The temperature insensitive long‐range oscillatory potentials are found and the wavelength of the oscillations observed is in good agreement with that expected from the electron theory of metals in all cases. The viscosity coefficient and surface tension were calculated and compared with experimental data.
High field transport in semiconductors. The drifted maxwellian approach. II. Application to n‐Insb
Authors: Stokoe T. Y. , Cornwell J. F. 
Published: July 2007

AbstractThe drifted Maxwellian approach to the transport properties of semiconductors is applied to Insb at high and low fields assuming Kane's model. Polar optical, acoustic, and ionised impurity scattering mechanisms are considered with band structure non‐parabolicity and the mixing of Bloch states with spin‐reversal effects being taken into account. The inclusion of the mixing of Bloch states leads to an increase of 17% in the low‐field mobility of Insb at 77 °K. Consistency between theory and experiment is obtained by taking Sanderson's static dielectric constant of 17.50, and Ehrenreich's acoustic deformation potential of −7.2 eV. A deformation potential of −30 eV seems inappropriate.
On the decay of the excited triplet state of the M centre in KCl
Authors: Bertolaccini M. , Bosi L. , Spinolo G. 
Published: July 2007

AbstractThe results of lifetime measurements of the relaxed excited triplet state of the M centre, 3M*, in KCl are given. The emission has the same decay time constant when exciting in the 1M and in the 3M bands: τ = τ(1M*). The conclusion may be drawn that a conversion 3M* → 1M* occurs with high probability.
Relativistic theory of low energy electron diffraction: Formalism and application to KKRZ‐pseudopotentials
Authors: Feder R. 
Published: July 2007

AbstractA relativistic theory for calculating low energy electron diffraction intensities and spin polarizations is developed. The presentation of the general framework is followed by the construction of a relativistic KKRZ‐type electron–ion‐core pseudopotential and subsequent application of the framework to a crystal model that consists of this potential plus a complex self‐energy part to incorporate inelastic effects.
X‐ray photoemission studies of the electronic structure of rare earth metals
Authors: Hedén P. O. , Löfgren H. , Hagström S. B. M. 
Published: July 2007

AbstractX‐ray photoemission (XPS) measurements are reported on evaporated films of the rare earth metals Eu, Gd, and Yb. For comparison additional measurements are reported on Ba. The results provide an unambiguous determination of the 4f energy levels. In Yb the spin–orbit splitting is also clearly resolved. The locations of the 4f levels below the Fermi level are determined to be 2.1 eV for Eu, 7.7 eV for Gd, and 1.4 eV and 2.7 eV for Yb all with an error of ± 0.4 eV.
The radiationless transfer of electronic excitation energy between impurity atoms in crystals characterized by broad absorption and luminescence bands
Authors: Kudžmauskas Š. P. , Batarňas J. V. 
Published: July 2007

AbstractThe theory of the energy transfer of electronic excitation between impurity atoms is developed for the case when broad absorption and luminescence bands exist. Perturbation theory is not employed. The probability of transfer is defined by a change of the quantum yield of the secondary donor radiation. The results are compared with the Förster‐Dexter theory.
Lattice dynamics and elastic constants of holmium and yttrium
Authors: Menon C. S. , Rao R. Ramji 
Published: July 2007

AbstractThe lattice dynamics and the elastic constants of the hexagonal metals holmium and yttrium have been investigated using the approach of Keating. In holmium, the dispersion curves are fitted using eleven force constant parameters and the six elastic constants are evaluated. The dispersion relations and the elastic constants of yttrium are fitted using twelve parameters.
Excitons in ZnS crystals with stacking faults
Authors: Ryskin A. I. , Suslina L. G. , Khilko G. I. , Shadrin E. B. 
Published: July 2007

AbstractThe exciton reflection spectra of ZnS crystals with stacking faults have been investigated at 4.2 °K. It has been found that in the range of available concentration of stacking faults (0 <α<0.35) (and especially at α = 0.1 to 0.2) the shift and splitting of the ground state (n = 1) exciton lines are considerably smaller than it should be expected in the case of linear dependence of these values on α. Spectra of ZnS crystals with a high concentration of stacking faults (α = 0.3) have a doublet structure of the B exciton line. It has been shown that this effect is due to the exchange interaction of the ground exciton state in ZnS crystals. An analogy between the spectra of crystals with stacking faults and the spectra of sphalerite crystals under tension along 〈III〉 is pointed out. The study of the spectra of ZnS crystals with stacking faults has shown that the exchange interaction of the excited exciton state does not need to be considered.
Angular‐correlation data analysis in terms of positron trapping by vacancies in metals
Authors: Kusmiss J. H. , Goland A. N. , Snead C. L. 
Published: July 2007

AbstractCross sections and rates for the trapping of positrons by vacancies in Aj, Cd, In, Zn, and Cu are derived from measurements of the angular correlation of positron‐annihilation radiation. The assumptions which usually accompany the application of the trapping model to angular‐correlation data are discussed in some detail.
Weak magnetic field enhancement of the luminescence from F centre pairs in alkali halides
Authors: Jaccard C. , Ruedin Y. , Aegerter M. , Schnegg P.‐A. 
Published: July 2007

AbstractWhenever a member of a F centre pair is excited optically at low temperature, it can return to the ground state either radiatively or by formation of a F′ centre, the excited electron being transferred by a fast tunnel effect to the neighbouring centre. This process is dependent on the spin symmetry of the pair, which is in turn determined by the competitive influence of the different local hyperfine fields and of an applied magnetic field. The latter causes a decrease of the tunnelling probability, i.e. an increase of the luminescent yield in two steps; the first critical value is given by the hyperfine field and the second one by the temperature according to the Boltzmann factor. The quantum yield is found to have an exponential dependence of the concentration, of the volume in which tunnelling is possible, and of the average tunnelling frequency. Spin‐lattice relaxation and EPR, by mixing between the spin state populations, reduce the effect. Application of the theory to experimental values obtained for the luminescence intensity as a function of the applied field in KI, KCI, and KBr yields the average tunnelling frequency (about ten times the radiative probability), the effective range (85 Å), and the absolute value of the luminescent quantum yield.
Diffusion theory of luminescent emission from a doped organic solid
Authors: Selsby R. G. , Swenberg C. E. 
Published: July 2007

AbstractUsing a rate equation for exciton diffusion, with a new theory for the probability per second of exciton capture by impurity traps, the time dependence of the luminescent emission from a doped organic solid for both impurity and host is calculated. The satisfactory agreement of this theory with recent measurements indicates that exclusion of diffusion as the major means of excitation energy transfer is premature.
The optical properties of GaAs:Co
Authors: Baranowski J. M. , Grynberg M. , Magerramov E. M. 
Published: July 2007

AbstractThe absorption due to optical transitions from the valence band to empty cobalt‐acceptor states in GaAs has been investigated. The results are well explained in terms of Lucovsky's model, and the hole ionization energy of 0.14 eV was determined. The crystal‐field spectrum of the 3d7 configuration is observed when the acceptor states are filled by electrons from shallow donors. The experimental results indicate that the acceptor state is due to hole in 3d‐shell of the cobalt impurity on substitutional gallium sites.
Frequency distribution function of solid ammonia
Authors: Goyal P. S. , Dasannacharya B. A. , Thaper C. L. , Iyengar P. K. 
Published: July 2007

AbstractThe frequency distribution function, g(ω), for solid ammonia has been derived from neutron inelastic scattering experiments at 106° K. It is used to calculate the specific heat and to analyse it in terms of Debye temperatures for translational and rotational parts. A comparison of the Debye temperatures with those obtained from the measured specific heat shows an excellent agreement up to 100°K, suggesting that the anharmonicity is not large below this temperature. Translational and rotational moments of the frequency distribution function calculated from the obtained g(ω) and the specific heat data are found to agree within about 10%.
Anslysis of piezospectroscopy of defects in wurtzite‐type crystals
Authors: Goede O. 
Published: July 2007

AbstractA general analysis is made of the effect of uniaxial stress on optical transitions between localized electronic states in wurtzite‐type crystals. The energy shift, the splitting pattern, and the polarization of no‐phonon lines are derived for the different defect symmetries and stress directions. It is shown that the piezospectroscopy of defects in wurtzite‐type crystals enables an unambiguous determination of the symmetry group of the defect and may yield valuable informations on the symmetry of the electronic states involved.
Retardation Effects in the Theory of Sensitized Luminescence in Molecular Crystals
Authors: Golubov S. I. , Konobeev Yu. V. 
Published: July 2007

AbstractA theory is given of the effective dipole‐dipole interaction between two identical interstitial guest molecules at large intermolecular distances the effects of retardation of the interaction taking into account. The corresponding generalization of the well‐known Förster‐Dexter formula of the electronic excitation energy resonance transfer in solids is found.
Some Thermomagnetic and Adiabatic Effects in Heavily Doped Semiconductors at Low Temperatures for Weak Magnetic Field
Authors: van Cong H. , Mesnard G. 
Published: July 2007

AbstractThermomagnetic and adiabatic effects at low temperatures for weak magnetic fields are investigated by a simplified model of heavily doped semiconductors. The treatment is based on the Green's function methods, using the Feynman‐path integral formulation, applied to disordered systems and developed already in six previous papers. Two typical cases concerning the relation between the carrier and donor concentrations are discussed.
The Change of Model Potentials in Alloying
Authors: Taut M. , Paasch G. 
Published: July 2007

AbstractThe different influences giving rise to a change of the screened form factors of model potentials in alloying are discussed. A special problem is the evaluation of the Fermi energy and the energy shift. The method for the calculation of these quantities proposed by Animalu and Heine for pure metals is not applicable to alloys. A new systematic perturbation treatment is developed to evaluate these quantities for pure metals, dilute and ordered alloys. The Shaw model potential is used. Numerical results are given for pure metals and dilute alloys. For the latter a change of the parameters of the bare model potential smaller than 3% is found giving only a small influence on the residual resistivity. This indicates that the assumption that the bare model potential of an ion is nearly independent of its surroundings is quite good. Approximations for the calculation of the change of the depletion hole are investigated also.
Relation of Long‐Range Interatomic Interactions to the Sign and Type of Short‐Range Ordering in Alloys
Authors: Katsnelson A. A. 
Published: July 2007

AbstractThe relation of long‐range interatomic interactions to the sign and type of short‐range order is investigated in alloys. It is found, that sign and type of short‐range order are determined by the spectrum of the ordering energy, which may be obtained from the dependence of the interatomic interaction potential on the distance. It is shown in the approximation of spherical Fermi surfaces, that an electron concentration of n = 1 causes a short‐range ordering of Cu3Au‐type. Both, increasing and decreasing of n give rise to a change of the type and then of the sign of the short‐range order.
Quantum Theory of Free Carrier Absorption
Authors: von Baltz R. , Escher W. 
Published: July 2007

AbstractThe theory of photon absorption by free carriers in degenerate semiconductors is given taking into account the influence of nonparabolic energy bands and the effects of scattering by impurities, phonons, and plasmons. Analytical formulas for the imaginary part of the dielectric function, ϵ2(ω), are derived. The quality of the asymptotic expansions of ϵ2(ω) for low and high photon energies to approximate ϵ2(ω) over a wide range of frequencies is investigated numerically. It is found that within a few percent the classical Drude theory gives an excellent approximation for photon energies up to twice the Fermi energy of the electrons. In the opposite case, the approximation for high photon energies gives a rather poor approximation of ϵ2(ω) near the Fermi energy, except for ionized impurity scattering.
Résonance paramagnétique acoustique de TiO2: Cr irradié
Authors: Boiteux M. , Doussineau P. , Ferry B. 
Published: July 2007

AbstractDes monocristaux de rutile contenant du chrome et irradiés aux rayons γ ont été étudiés au moyen de la résonance paramagnétique acoustique. La présence de raies dues à l'ion Cr3+ a été établie et deux constantes de couplage spin‐phonon de Cr3+ ont été mesurées: |G44| ≈ 3 cm−1 et |G66| ≈ 7 cm−1. L'attribution de raies supplementaires aux ions Cr2+ et Cr4+ est discutée.
Energy of Screw Dislocations in Metals
Authors: Simon G. 
Published: July 2007

AbstractThe contribution of the band structure energy to the energy of a screw dislocation in a metal is calculated within the framework of pseudopotential theory. The total energy of the dislocation is the sum of the change in electrostatic energy of the point‐ion lattice and the band structure energy. Numerical results are given for the alkali metals using Ashcroft's atom form factors.
Estimation of the Influence of Lattice Resonant Modes on the Nuclear Quadrupole Spin–Lattice Relaxation
Authors: Mühle E. 
Published: July 2007

AbstractThe influence of nonparamagnetic point and line defects in the crystal lattice on the nuclear quadrupole spin‐lattice relaxation is studied. Under the assumption of simple models for defects in a cubic lattice it is shown that lattice resonant modes cause at low temperature an increase of the local relaxation rate around the defects. The efficiency of spin diffusion is estimated. Measurable effects are expected only with relatively high concentrations of defects.