X-band EPR study on benzo[c]cinnoline single crystals

The benzo[c]cinnoline compound has been crystallized in ethanol solution. These crystals have been irradiated with ⁶⁰Coγ-rays at room temperature. The crystals have been investigated by an X-band electron spin resonance (ESR) spectrometer two days after irradiation. Very strong ESR peaks have been observed at the temperatures between 130 and 430 K. However, a line broadening has been observed at 130 K. Also analyses found that EPR specra are temperature-dependent and show anisotropic behaviour.     

Thermoluminescence and photoluminescence studies on gamma irradiated CsI: Pb2+ crystals

Pure and Pb²⁺-doped CsI crystals have been grown by the Bridgemann technique. Optical absorption, thermoluminescence (TL) and photoluminescence (PL) measurements have been performed. In undoped and Pb²⁺-doped cesium iodide crystals, F-centers and V-centers have been produced at 770 nm and 350 nm, respectively. In Pb²⁺-doped crystals, additional centers at 373 nm, 290 nm and 258 nm bands have been produced. In undoped samples, only two glow peaks at 343 K and 373 K have been produced, and in Pb²⁺-doped samples additional glow peaks at 383 K and 423 K have been produced. For all the samples, TL emission, PL and excitation measurements have been performed.     

钽铌酸锂晶体的布里渊散射研究

研究了钽铌酸锂(LiTa_xNb_(1-x)O_3,x=0.0013,0.0052,0.015,0.06)晶体在室温的布里渊散射.给出了它们的弹性刚度常数和压电应力常数.测量了一种组份晶体的布里渊散射频移在50K～580K范围内的温度特性.发现某些声子散射谱中除三个正常峰外还存在一个异常峰.     

Peculiar aspects of galvonamagnetic properties of InS single crystals

The electrical conductivity and the Hall effect in electronic InS single crystals have been studied over a wide range of temperatures, from 150 K to 800 K, and their peculiarities have been elucidated. At temperatures of 200 K the Hall coefficient passes through a maximum but does not reach a minimum. The peculiarities of the temperature dependence of the Hall coefficient are explained within the two-band model, which incorporates the conduction band and the impurity band. The parameters of the impurity band have been determined. The hopping mechanism of scattering has been found to predominate in InS single crystals in the temperature range 150–270 K, and at temperatures of 270 K to 400 K the mobility is limited, mainly by scattering on impurity ions. Above 400 K electrons are scattered on polar lattice vibrations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 29–34, January, 1989.     

Anomalies in the scattering of gamma-rays from single crystals of HF-doped ice-I h around 100 K

Using the high energy resolution of the Mössbauer effect, the elastic and inelastic scattering of gamma-rays from single crystals of HF-doped IceI _h has been distinguished. The crystals were studied in the region of 100 K, since measurements by previous workers have suggested the possibility of an order-disorder transition at this temperature. Marked anomalies in the scattered intensity were observed between 106 and 125 K, and these were shown to depend on the thermal history of the crystals.     

Studies of phase transitions and ferroelastic domain walls in Pb5Al3F19 crystals by optical measurements

Three phase transitions between 100 and 400 K were previously shown by X-ray diffraction measurements. Such results have been confirmed by optical measurements on crystals. The thermal dependence of the birefringence has been determined. A new phase transformation has been shown at around 590 K not only by optical study but also by dielectric measurements. Ferroelastic domain-walls have been visualized. The sequence transition has been discussed taking into account the various space groups.     

EPR study of radiation damage in gamma-irradiated 3-nitroacetophenone single crystal

This paper presents the results of the electron paramagnetic resonance (EPR) study of the anion radical formed from 3-nitroacetophenone (C₈H₇NO₃) (3NAP) single crystal, by gamma irradiation. The EPR spectra of gamma-irradiated single crystals of 3NAP have been recorded at 10-degree intervals for different orientations of crystals in a magnetic field, at room temperature. The EPR analysis of gamma-irradiated crystals of 3NAP has shown that the radiation damage center produced by gamma irradiation is the carbon-centered 3NAP anion radical. One-electron reduction of 3NAP results in general bond loosening. The single crystals have been investigated between 120 and 450?K. The spectra have been found to be temperature-dependent. The EPR parameters of the 3NAP anion radical have been evaluated.     

A spectroscopic study of the intermolecular photodimerization of 1-(9-anthryl)-3-(1-naphthyl)propane

Single crystals of the intermolecular photodimer of 1-(9-anthryl)-3-(1-naphthyl)propane have been prepared. The photophysical properties of this molecule as well as the sandwich dimer obtained by photocleavage in methylcyclohexane at 77 K have been recorded. A qualitative study of the photochemical properties of the sandwich dimer in single crystals of the photodimer host shows that the photochemical mechanism is similar to those of the anthracene sandwich pair and the anthracene-naphthalene pair.     

The spectroscopic investigation of the fluorescence decay time of the anthracene crystal

Using single-photon counting technique measurements of fluorescence decay curves of anthracene crystals have been performed at room and 4.2°K temperatures. Different lifetimes have been found in different emission lines at 4.2°K. The fluorescence rise in some emission lines of intrinsic luminescence has been interpreted as a result of two-step mechanism of excitonic fluorescence of the anthracene crystal.     

<Superscript>29</Superscript>Si nuclear spin relaxation in microcrystals of plastically deformed Si: B samples

Single crystals and microcrystals Si: B enriched with ²⁹Si isotopes have been studied using nuclear magnetic resonance and electron paramagnetic resonance (EPR) in the temperature range from 300 to 800 K. It has been found that an increase in the temperature from 300 to 500 K leads to a change in the kinetics of the relaxation of the saturated nuclear spin system. At 300 K, the relaxation kinetics corresponds to direct electron–nuclear interaction with inhomogeneously distributed paramagnetic centers introduced by the plastic deformation of the crystals. At 500 K, the spin relaxation occurs through the nuclear spin diffusion and electron–nuclear interaction with an acceptor impurity. It has been revealed that the plastic deformation affects the EPR spectra at 9 K.     

Discontinuous creep curves of Cd+0·44 at.% Zn alloy single crystals

The creep behaviour of Cd+0·44 at.% Zn alloy single crystals is described. Contrary to the Cd single crystals discontinuous creep curves have been observed, which do not occur at 78 K. The low- temperature limit of this effect is 130 K approximately. The characteristics of these discontinuous creep curves are discussed on the assumption that the Portevin-Le Chatelier effect is acting in the Cd+0·44 at.% Zn alloy.     

Elaboration,caracterisation et proprietes magnetiques de cristaux d'oxyde Sm2O3

Single crystals of samarium oxide Sm₂O₃ with monoclinic B structure were prepared by the Verneuil process adapted to a plasma torch. Some properties of these crystals have been studied (cleavage, hardness …) especially the magnetic properties. Paramagnetic susceptibilities measurements have been performed for various orientations of the crystal with respect to the magnetic field at constant temperatures (5, 77, 300 K) as well as at increasing temperatures (5–1000 K) and indicate an anisotropy. An interpretation of this phenomena is proposed.     

Proton N.M.R. of trismethylenemethaneiron tricarbonyl in a nematic liquid crystal

Single crystals of the cycloadduct of 1-(9-anthryl)-3-(1-naphthyl)propane (CANP) have been prepared, enabling a photochemical and photophysical study to be made of the anthracene-naphthalene sandwich pair in this material. The low temperature fluorescence spectrum is broad, exciplex in nature, and has a decay time of about 80 ns. This emission is quenched as the temperature is raised by a process which involves photocyloaddition of the pair. Arrhenius plots give an activation energy of about 600 cm^-1 for the photochemical process. The analogous photophysical properties have also been studied in methylcyclohexane glasses at 77 K and 60 K. Formation of the sandwich pairs at 77 K gives rise to a ‘ partially relaxed ’ pair having some structure in its emission spectrum and a shorter lifetime. Possible reasons for the differences in properties of sandwich pairs in methylcyclohexane glasses and the parent cycloadduct crystals are discussed. Very weak emission from the naphthalene moiety of monomer ANP has been observed at 77 K.     

Gamma-radiolysis of deaerated cysteine solutions

The electron paramagnetic resonance (EPR) spectra of gamma-irradiated single crystals of phenidone (fenidon C₉H₁₀N₂O) have been studied for different orientations of crystals in a magnetic field. Phenidone single crystals have been irradiated with ⁶⁰Co-γ rays at room temperature. The EPR spectra have been investigated at temperatures between 125 and 450 K. The spectra have been found to be temperature independent. The spin-Hamiltonian parameters have been obtained from the single-crystal EPR analysis. The principal values of the hyperfine coupling tensor of the unpaired electron and the principal values of the g-tensor have been determined.     

Study of the trapping states in ZnS single crystals grown from gallium melt

The trapping levels in zinc sulphide single crystals grown from gallium melt have been investigated using thermoluminescence techniques. The observed peak at 175° K consists of two overlapping components at 173 and 200° K respectively. Thermal activation energies and frequency factors were calculated for both traps. The dependence of glow curve shape on excitation conditions is caused by the retrapping by non-filled 200° K traps of electrons freed from 173° K traps in the course of the glow curve run. In addition to the results on “pure” crystals, measurements were made on samples grown with chlorine, oxygen and copper impurities, as well. Although no positive identification of the chemical nature of the 173 and 200° K trapping centers has been possible, we find that our results are not inconsistent with a previously suggested model in which the traps are identified as complex defects. Comparison is also made with trap spectra observed earlier in gallium-doped zinc sulphide samples prepared by the usual methods.     

Polarization of the terahertz radiation of uniaxially compressed p germanium at the electrical breakdown of a shallow acceptor impurity

The spectral and polarization investigations of spontaneous terahertz radiation under the conditions of the electrical breakdown of shallow acceptors (gallium) in germanium crystals have been reported. The radiation spectra of crystals uniaxially compressed in the [111] direction at a pressure of about 3 kbar, as well as undeformed crystals, have been measured at T = 5 K using a Fourier spectrometer with step scanning. The polarization of radiation has been estimated for transitions of holes between various states of a shallow acceptor in uniaxially compressed germanium. To identify the observed radiation lines, their experimental energies and polarizations have been compared to the respective calculated values. The spectral lines corresponding to the transitions of holes from the resonance state to the excited states of acceptors have been identified.     

On the role of hole trapping centers in the interactive mechanism of the trap interaction in anion-defect alumina single crystals

The effect of deep hole traps on the intensity and shape of the dosimetric peak of thermoluminescence (TL) has been studied at 450 K in anion-defect alumina single crystals. It has been shown that filling of deep hole centers leads to a decrease in the sensitivity to radiation of crystals with a small half-width of the TL peak and has no effect on the sensitivity of crystals with a broadened peak. It has been assumed that traps responsible for the TL dosimetric peak broadening are of hole nature, which can be caused by the presence of Ti3+ ions in the corundum lattice. The results obtained have been interpreted within the modified model of the interactive system of traps.     

X-ray and thermoluminescence of LiKB4O7 single crystals

The thermoluminescent (TL) and X-ray luminescent (XL) spectra of undoped LiKB₄O₇ (LKBO) single crystals had been investigated in the temperature range 80-300 K. It was found that in LKBO crystals, there are two intensive TL peaks at 112 and 132 K. The only one band emission spectra of sharply defined Gaussian shape, confirming the same mechanism of XL and TL by the radiation annihilation of the strongly localized self-trapped excitons (STE), had been observed in the TL and XL spectra. The possible models of these localization centers STE have been discussed.     

Phase transitions in AgTaO3 single crystals

AgTaO₃ single crystals have been obtained by the molten salt method; two different solvents, AgCl and V₂O₅, were used. X-ray investigations have been carried out in the temperature region from 300 K to 800 K. At room temperature AgTaO₃ possesses a pseudocubic perovskite-type unit cell with rhombohedral distortion. Two structural phase transitions, to tetragonal at 650 K and to cubic symmetry at 770 K, have been observed. In the tetragonal phase a jump of the lattice constants has been observed at approximately 680 K. DTA and domain structure investigations confirm the presence of these phase transitions.     

Electron paramagnetic resonance study of irradiated tetramethyl-4-piperidion

The electron paramagnetic resonance of single crystals of tetramethyl-4-piperidion (TMP; C₉H₁₉NO) has been observed and analysed for different orientations of the crystal in the magnetic field, after being damaged at 300 K by γ-irradiation. The crystals have been investigated between 100 and 450 K. The spectra were found to be temperature dependent. The irradiation of TMP by γ-rays produces radicals at the nitrogen atoms in the molecule. The principal values of the hyperfine coupling tensor of the unpaired electron and the principal values of the g-tensor were determined. The results were found to be in good agreement with the existing literature data and theoretical predictions.