Paradoxes of the influence of small Ni impurity additions in a NaCl crystal on the kinetics of its magnetoplasticity

A comparative study of magnetoplasticity in two types of NaCl crystals differing in impurity content only by a small Ni addition (0.06 ppm) in one of them, NaCl(Ni), has been carried out. Two methods of sample magnetic exposure were used: in a constant field B = 0–0.6 T and in crossed fields in the EPR scheme—the Earth’s field B_Earth (50 μT) and a variable pumping field \(\tilde B( \sim 1 \mu T)\) at frequencies ν ~ 1 MHz. In the experiments in the EPR scheme, the change of the field orientation from \(\tilde B \bot B_{Earth}\) to \(\left. {\tilde B} \right\|B_{Earth}\) led to almost complete suppression of the effect in the NaCl(Ni) crystals and reduced only slightly (approximately by 20%) the height of the resonance peak of dislocation mean paths in the crystals without Ni, with the amplitude of the mean paths in NaCl(Ni) in the orientation \(\tilde B \bot B_{Earth}\) having been appreciably lower than that in NaCl. In contrast, upon exposure to a constant magnetic field, a more intense effect was observed in the crystal with Ni. The threshold pumping field amplitude \(\tilde B\), below which the effect is absent under resonance conditions, for the NaCl(Ni) crystals turned out to be a factor of 5 smaller than that for NaCl, while the thresholds of a constant magnetic field coincide for both types of crystals. All these differences are discussed in detail and interpreted.     

Kinetics of recombination interaction of impurity centers in crystal phosphors

Various nonlinear regimes of stationary emission of crystal phosphors with several types of impurity centers are investigated. In the case of two types of centers (radiative and nonradiative recombination), general equations are derived which connect the emission yield with the volume density of the excitation, given the temperature and the parameters of these centers. The degree of nonlinearity K and the temperature sensitivity R_T are obtained for various ratios of the parameters of the centers and for definite ranges of excitation conditions. The conditions needed to obtain anomalously high values of K and R T are established, and their limiting values upon saturation of the effective nonradiative-recombination centers are estimated. The diverse roles of the quenching processes in practical applications of crystal phosphors is discussed.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 117, pp. 3–54 (1980).     

Radio-frequency paramagnetic resonance spectra, detected from dislocation displacement in NaCl single crystals

Results are reported here of a study of the resonance effect of a constant magnetic field and a variable magnetic field crossed with it on the rate of macroplastic deformation and motion of edge dislocations in NaCl crystals. The frequencies of the variable magnetic field at which the maximum variations in the plasticity of the crystals are observed correspond to the resonant frequencies for transitions between the Zeeman sublevels in paramagnetic complexes of point defects and complexes consisting of a point defect and a dislocation. Analysis of the radio-frequency spectra obtained enabled us to establish the role of intercrystal reactions in the formation of the mechanical properties of the crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 1778–1784 (October 1999)     

Tunneling energy levels of an off-center impurity of the hydroxyl ion in NaCl crystal

Fine structures of the vibrational spectrum of OH^– in NaCl have been investigated by their dependence on the OH^– concentration, temperature and uniaxial stress. The absorption bands of A and C at 3651. 2 and 3655.2 cm-1 are ascribed to the tunneling motion of the off-center impurity of OH^–. The stress splitting factor of the tunneling levels has been estimated to be B(S11–S12)=0.96±0.10 cm-1/10⁸ dyn cm-2 in the ground state and it is about 1.4 times larger in the vibrational excited state.     

Low-frequency spectra of dislocation paths in NaCl crystals in the electron spin resonance scheme

It is shown that the criterion of dislocation mobility resonance in NaCl crystals in the electron spin resonance scheme in the Earth’s magnetic field depends on both the sample orientation in this field and the location of impurity atoms in the dislocation core. The measured low-frequency spectrum of dislocation paths makes it possible to resolve a series of peaks corresponding to different positions of a Ca impurity that correlate with the results from computer simulations of the dislocation core structure.     

Theory of vibronic optical spectra of impurity centers with violation of the Condon approximation

Expressions for non-Condon generating functions of absorption and luminescence of optical centers in crystals at zero temperature have been obtained in the adiabatic approximation. A solution to the Schrödinger equation for an electronic subsystem has been considered to the first order of the perturbation theory for a vibronic interaction linear in normal coordinates of the vibrational subsystem. The non-Condon form function of the optical transition has been obtained in the form of a convolution operator acting on the normalized Condon form function. It has been proved that, if the optical transition is forbidden in the Condon approximation due to symmetry, the non-Condon form function does not contain a zero-phonon line and the non-Condon form functions of absorption and luminescence are symmetric.     

EPR spectra of Mn2+ ions in precipitated divalent impurity phases in monocrystalline NaCl

The EPR spectra of Mn²⁺ ions embedded into precipitated phases of Mg²⁺, Cd²⁺, Fe²⁺ and Ca²⁺ in NaCl single crystals have been investigated. The spectrum from samples whose major impurity is Mg, Cd or Fe corresponds to Mn²⁺ substituting some divalent cation inside the Suzuki phase (6NaCl.MCl₂). The existence of such a phase has been ascertained by means of Raman spectroscopy. On the other hand, the EPR spectrum of Ca²⁺ doped samples has been attributed to Mn²⁺ inside various CaCl₂ precipitates.     

Peierls-Nabarro model of the core of edge dislocation in Sm A liquid crystal

The core structure of an edge dislocation in Sm A liquid crystal is analysed by using the Peierls-Nabarro method. The stress necessary for a glide motion of dislocation and the dislocation core energy are estimated.     

Diffusion in dislocation germanium and the model of a liquid dislocation core

Experimental data on the diffusion of ⁷¹Ge, ¹¹³Sn, ¹¹⁴In, and ¹²⁴Sb isotopes in dislocation germanium are discussed within the model of a liquid dislocation core and the filament model of diffusion along dislocations. The temperature dependences of the diffusion permeability along the dislocations are matched to the corresponding temperature dependences of the coefficient of diffusion in the melt in order to determine the absolute values of the coefficient of diffusion along dislocations and the effective diffusion radius of the dislocation core. The experimental results are discussed in terms of thermodynamic parameters of the liquid state and the parameters of diffusion in the melt. The results obtained are consistent with the cooperative diffusion mechanism and the mechanism of diffusion through relaxed vacancies.     

Point-defect interaction in a dislocation core

By minimizing the thermodynamic potential we derive formulas for equlibrium length-distributions of dislocation segments and one-dimensional clusters formed from point defects in a dislocation core. The theoretical formulas are compared with results of computer modeling. Temporal variations of cluster-formation processes are discussed. Plots of the number of clusters and average and maximum lengths of clusters and dislocation segments as functions of time are presented. Moscow Technological University of Steel and Alloys. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 74–81, April 2000.     

Theory of an impurity state in a crystal

A review is given of the theory of the effects of single-, or low-concentration impurities on the properties of otherwise perfect crystals. The subjects considered include electron density, anomalies in the temperature dependence of the spontaneous magnetization of a ferromagnetic insulator and the spectrum of lattice vibrations. All the problems are considered from a single mathematical point of view in which the approximation of localized perturbations and Green function techniques are used. The conditions for the occurrence of localized and virtual states are discussed. The review concludes with a formulation of the general methods of the theory.     

Study of vibronic interactions in impurity centers by conjugate fluorescence and absorption spectra with a poorly resolved vibrational structure

The conjugate fluorescence and fluorescence excitation spectra of recently synthesized substituted arylpolyene (C₆H₅-[CH=CH]₂-C₆H₄-NH₂) are studied in solid n-octane at a temperature of 4.2 K. The spectra exhibit a weakly pronounced vibrational structure. A method of determination of the vibronic interaction parameters responsible for the shape of the spectra is developed. The method is based on the modeling of the spectra by series of vibronic bands, each of which consists of a narrow zero-phonon line and a broad phonon wing (phonon sideband). This makes it possible to calculate the fluorescence and fluorescence excitation spectra with the weakly pronounced vibrational structure and compare them with the measured spectra. The deviations from the mirror symmetry between the measured fluorescence and fluorescence excitation conjugate spectra are explained by the combined effect of the Franck-Condon and Herzberg-Teller interactions. The parameters of these interactions are determined.     

Aggregation of impurity centers in ionic crystals

Results of modeling of the aggregation process in complex centers of ionic crystals are presented. Concentration dependences of the number of paired centers are obtained. A nature of the paired luminescence centers is discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 62–65, February, 2007.     

Determination of shallow core level spectra in selected compound semiconductors

Core level spectra of the M shells of Ga, Ge, As, and Se and of the L shell of S have been obtained from X-ray photoemission measurements on GaAs, GeSe, and GeS. Broadening contributions from the achromatic source, the analyzer momentum window, and the extrinsic losses experienced by the photoemitted electrons in traversing the solid, as well as satellite lines due to K_3,4 emission, are removed by deconvolution of the data with a measured electron backscatter spectrum convoluted with a source function. The results are compared with theory where available.     

Certain characteristics of the energy spectra of impurity centers and charge-carrier scattering processes in high-resistivity GaAs(O)

The behavior of electron and hole mobilities in illuminated high-resistivity single crystals of oxygen-doped gallium arsenide has been investigated and compared with the behavior of these parameters in the unilluminated specimen. A complete liquidation of charged centers was observed at temperatures below 50°K which shows that these crystals do not contain shallow donors or acceptors. The electron-to-hole mobility ratio in the neutral-center scattering region has also been determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.2, pp.25–34, February, 1976.In conclusion the authors express their appreciation to V. B. Dik for designing and constructing the helium cryostat and to M. S. Al' Kuveiti for performing some of the measurements of dark characteristics of some of the samples.