Thermally stimulated depolarization currents in LiF+Be2+

The reorientation of dipolar complexes in a LiF single crystal doped with Be²⁺ has been studied by means of the thermally stimulated depolarization currents technique (T.S.D.C) in the temperature region 80–300 K.Three main bands were observed. The low temperature band has an enthalpy smaller by a factor of two than the intermediate band. The enthalpy of the latter is comparable to that of the migration process of the free cation vacancy but smaller (i.e. by 40%) than the enthalpy of the high temperature band. The general behaviour is similar to that of the systems: KCl + Be²⁺ and NaCl + Be²⁺ studies two decades ago.     

Size distribution of metallic colloids in alkali halide single crystals

The size distribution of Ag colloids in KCl single crystals reported by Jain and Arora is compared with the predictions of a theoretical model proposed by the authors.     

Local structure and lattice dynamics of alkali halide crystals with an anion vacancy

The local structure and vibrations in the region of an anion vacancy are studied using the pair interionic potentials within the shell model for crystals Me ⁺Cl^? (Me ⁺ = Rb⁺, K⁺, Na⁺). The pair potentials are derived from first-principles calculations of different clusters by the Hartree-Fock-Roothaan method with the one-electron states constructed in the form of molecular orbitals as linear combinations of atomic orbitals (MO LCAO). The calculations are performed with the GAMESS program package (US). The correlation corrections are included in the calculations. The validity of the model parameters is verified by comparing the calculated with experimental structural and dynamic properties of ideal alkali halide crystals.     

Thermally stimulated and photo-stimulated conductivity in ZnS-Cu single crystals

The development of thermally stimulated and photo-stimulated conductivity in zinc-sulfide phosphors has been studied. The sign of the charge carriers in the single crystal samples inspected has been determined. The effect of infrared light in the region 1–3.5 m upon previously excited crystals has been investigated and the temperature dependence of the photostimulated conductivity established.In conclusion, the authors express their deep gratitude to E. S. Bespalovaya for the samples and also to K. Arun for his help in measuring the Hall constant.     

Thermally stimulated depolarization of human blood

Thermally stimulated current spectra of human blood preparations are investigated. The electret effect in blood is interpreted using the fundamental concepts of the electret state of matter and electrical polarization of biopolymers. It is speculated that the electret effect in blood is related to the biological cycles in the organism and associated biochemical processes. It is noted that the method of thermally stimulated current is appropriate for express diagnostics of biological objects.     

Optical and electron spin resonance spectra ofZ 2(Eu) centers in alkali halide crystals

The ESR spectra ofZ ₂(Eu)-centers in KBr and KCl are presented and correlated to the optical absorption and the electron spin resonance of the Europium vacancy complex. The fine structure of theZ ₂ spectra can be described by a Spin-Hamiltonian with an axialb ₂ ⁰ -parameter only. At room temperature it amounts to 1,761 10^–4 cm^–1 for KBr, 1,854 10^–4 cm^–1 for KCl and 1,453 10^–4 cm^–1 for RbCl. Accordingly theZ ₂(Eu)-center must posses a strict axial 100-symmetry in these crystals.     

Thermally stimulated current measurements in as-grown TlGaSeS layered single crystals

Charge carrier traps in as-grown TlGaSeS layered single crystals were studied using thermally stimulated current measurements. The investigations were performed in temperatures ranging from 10 to 100 K. The experimental evidences were found for the presence of one shallow hole trapping center in TlGaSeS, located at 12 meV from the valence band. The trap parameters have been calculated using various methods of analysis, and these agree well with each other. Its capture cross-section and concentration have been found to be 8.9 × 10⁻²⁶ cm² and 2.0 × 10¹⁴ cm⁻³, respectively. Analysis of the thermally stimulated current data at different light excitation temperatures leads to a value of 19 meV/decade for the shallow hole traps distribution.     

The effect of electron irradiation on some alkali halide single crystals

The investigated alkali halides (Nacl, KCl, RbCl and CsCl) decompose under electron irradiation into alkali metal colloids and chlorine gas. This decomposition is a special case of radiation damage effects, which strongly influence the crystalline structure and the physical properties of the crystals under investigation. The decomposition process consists of the breaking up of the single crystalline material into polycrystalline aggregates; at the same time cavities, or larger aggregates of vacancies are produced, which, together with the boundaries of the polycrystalline aggregates, serve as the nuclei of growing dark platelets, which appear to be precipitated alkali metal crystals.We wish to thank Prof. Dr. S. Lengyel, director of our laboratory, for his helpful assistance in securing the necessary means, and his interest. We further thank Mrs. L. Fülöp, who carried out the electron-microscopic preparatory work and helped most effectively in taking and evaluating the electron micrograms and diffractograms. Finally we wish to thank R. Voszka, head assistant of the University, and J. Kis, research physicist, for valuable discussions.     

Thermally stimulated depolarization of a phosphate glass

Thermally stimulated depolarization (TSD) of phosphate glass of the composition 72·9% P₂O₅, 8·5% Al₂O₃, 18·6% CaO, 0·23% MnO has confirmed the existence of two types of slow relaxation. Migration polarization leads to TSD maximum near 0 °C, while the high temperature TSD maximum at 113 °C probably corresponds to space charge polarization. An analysis of the high temperature maximum shows that it is formed by a spectrum of relaxations with a single activation energy 1·0 eV, distributed over the dipole frequency factors with the most probable value ₀ 10¹⁰ sec^–1. Strong dispersion of permittivity points to the space charge polarization, though it is found that the effect is linear and independent of the sample geometry.The authors thank Dr. A.Bohun for the samples and for valuable advice.     

Debye temperature of alkali halide crystals

The Debye temperature _D is calculated from the elastic constants for 18 alkali halide crystals. Comparison of the results with calorimetric data _D reveals an agreement within the experimental error. The temperature dependence of _D is determined for NaCl, NaBr, KCl, and KBr crystals from the elastic constants, and this dependence is compared with the calorimetric data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp. 89–94, March, 1971.     

Optical breakdown of alkali halide crystals

It is shown that the metallization of a dielectric in the region of its interaction with laser radiation is a substantiated mechanism of laser damage of wide-gap dielectrics. Calculations of the radiation pressure produced by high-power laser radiation and the pressure of external bulk compression at which the dielectric energy-gap width becomes zero and which is calculated on the basis of the self-consistent statistical electron theory of ionic crystals have shown that these pressures are of the same order of magnitude.     

Healing of cracks in alkali halide crystals

The healing of micro-and macrocracks under local heating and x-ray irradiation of LiF single crystals is studied. The main features revealed in crack healing due to local actions are described. The contribution of the plastic zone formed upon the arrest and healing of a crack to the strength of the crystal is estimated.     

Lattice energy of alkali halide crystals

A new repulsive term in the ionic interaction potential ψ(r) = Ar^?ne^?r/gl, is suggested and the three unknown parameters A, λ and n are evaluated. Lattice energies of alkali halide crystals are calculated using this form. The results agree fairly well with the experimental values.     

Proton dechanneling in alkali halide mixed crystals

The effects of the lattice distortion in KCI-KBr mixed crystals on the dechanneling of 1.5 MeV protons are studied by means of backscattering. The dechanneling rate vs. the composition curve has a maximum at about 1:1 mixture of KCI and KBr. The lattice distortion in the mixed crystals is estimated from the dechanneling rate, and the result agrees well with that obtained by an X-ray measurement. The effective cross-section for the dechanneling caused by the lattice distortion is obtained, and compared with the results of a calculation based on a simple model.     

Luminescence of aggregate centers in CsBr:Eu2+ single crystals

We have used the Bridgman method to grow CsBr:Eu²⁺ single crystals, adding an activator to the mix in the form of Eu₂O₃ in amounts of 0.0125, 0.0250, and 0.0500 mole %. At T = 300 K, we studied the absorption spectra, the photoluminescence (PL) spectra, and the photostimulated luminescence (PSL) spectra of the grown crystals. We have established that the structure of the photoluminescence and photostimulated luminescence centers in crystals grown from the CsBr:Eu₂O₃ mix includes isolated dipole centers Eu²⁺-V_Cs, emitting in bands with maxima at 432 nm and 455 nm respectively, and in crystals grown at activator concentrations of 0.025 and 0.050 mole % they also include aggregate centers (AC) based on CsEuBr₃ nanocrystals with emission bands at 515 m and 523 nm. We have shown that the maximum concentration of aggregate centers of the CsEuBr₃ nanocrystal type in CsBr:Eu²⁺ crystals is achieved for an activator content in the mix within the range 0.01–0.05 mole %. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 359–362, May–June, 2006.