Oscillator strength of F2 − colour centres in LiF crystal

The absorption cross-section integral and the oscillator strength of the 960 nm absorption band due to F₂ ^– colour centres in LiF crystal is determined at room temperature from the absorption cross-section spectrum of the F₂ ^– centres obtained from saturable absorption studies. A comparison with previous results is made.     

Electrical conductivity of urea nitrate single crystal

The electrical conduction in urea nitrate single crystal has been found to be anisotropic. The conductivities measured in the directions parallel and perpendicular to the cleavage plane were 1.5 x 10^?8 and 1.2 x 10^?11 ohm^?1 cm^?1 at 300 K, respectively.     

Effect of colour centres (F′-centres) on the depolarization of positive mouns in KCl

The Korringa-Kohn-Rostoker-coherent-potential-approximation (KKR-CPA) method for treating electronic states in random alloys has been made charge self-consistent. Results are presented for a Ag_0.2Pd_0.8 alloy that were obtained using the Hedin-Lundqvist local density exchange-correlation potential.     

Observation of U centres in proton-irradiated KCl

Optical and infrared spectra of U centres formed by proton and deuteron irradiation of KCl are reported. The efficiency of formation of U centres is roughly one U centre per ten incident protons. U → F conversion by ultraviolet bleaching confirms that the implanted U centres behave in the same way as in chemically doped crystals.     

Electrical conductivity and stimulated thermocurrent studies in dicalcium lead propionate single crystal

Electrical conductivity and stimulated thermocurrent (stc) studies are carried out in dicalcium lead propionate (dlp) in pure, Cu²⁺, Fe³⁺ and acetate doped single crystals over a temperature range of 303° to 503° K. Conductivity measurements on pure and doped single crystals ofdlp indicate that both propionate anions and metallic cations are responsible for the transition occurring at 333°K. Thermoelectric power measurements from 340° to 500°K indlp (pure) indicate that the transport charge carriers are electrons. A model for the conduction mechanism is proposed on the basis of hopping ofπ or resonating electrons of carboxyl groups through tunnel paths involving metal ions (Pb²⁺ and Ca²⁺). From activation energies estimated from conductivity andstc measurements, thestc peak indlp (Fe³⁺) occurring at 513°K is attributed to impurity vacancy jump mechanism.     

Subhalides of tellurium: Electrical conductivity in relation to crystal structure

Subhalides of Te are compounds of the type Te_yX with y ?1 and X = Cl, Br, I. Within this group of compounds the structural building unit of elemental tellurium - the Te-screw with 3₁ or 3₂ symmetry - is continuously modified and yields a series of crystal structures from one-dimensional Te-Te arrangements to a zero-dimensional type. We show qualitatively how the electrical conductivity of these compounds is correlated to the various crystal structures. Gap energies are determined from the temperature dependence of the electrical conductivity.     

Auger emission and colour centres in lithium fluoride

Low energy Auger transitions from lithium fluoride, below 50 eV, have been associated by Gallon and Matthew [Phys. Status Solidi 41 (1970) 343] with transition processes between an ionised lithium ion and neighbouring fluorine ions. Two of these transitions, giving rise to lines at 36 eV and 43 eV were thought to involve de-excitation via colour centre defects. The growth behaviour of these lines has been investigated as a function of temperature, between 200°K and 600°K, and correlations have been established between this behaviour and optical absorption data obtained in situ. The effects of deposited nickel films on the Auger spectrum have also been investigated, and it is concluded that the 43 eV transition arises from lithium metal produced by electron beam dissociation of the lithium fluoride while the 36 eV line does indeed arise from de-excitation via a defect centre.     

Electrical conductivity of magnesium oxide single crystal below 1200 K

Using 2-, 3- and 4-electrodes configurations the direct current conductivity of MgO single crystals of nominally highest purity (with respect to cation impurities), grown by arc-fusion, was studied in argon or oxygen between 500–1200 K with special reference to both hysteresis effects during heating and cooling cycles and conductivity phenomena which occur underneath the surface in a thin subsurface zone. The samples contained 250–2500 at.-ppm carbon and typically 800 at.-ppm hydrogen.Below 1000 K the low temperature (LT) conductivity mechanism is characterized by an activation energy of 1.1 ± 0.2eV, distinctly lower than that of the high temperature region (HT) approximately 2.4 eV. By annealing at 300 K the LT mechanism progressively builds up and causes a very pronounced conductivity increase between 700–900 K, unaffected or even enhanced by O₂. Above 900 K, O₂ decreases the conductivity.The LT mechanism is proposed to be due to defect electrons on anion sites corresponding to O^? in the O^2? structure which are a consequence of the presence of carbon and hydrogen dissolved in the MgO and formally derived from the dissolution of traces of CO₂ and H₂O [J. Chem. Phys. Solids43, 129 (1982)].The dissolved carbon is known to segregate into the elastically relaxed subsurface zone (J. Chem. Phys. Solids43, 59 1982). The conductivity data suggest that between 700–900 K, defect species of C + 2O^?, the dipolar CO^?₂, which become strongly enriched in the subsurface zone upon annealing at 300 K, dissociate according to the equation CO₂^2?→CO^? + O^?, thus generating the defect electrons responsible for the LT mechanism.     

Decay of colour centres in natural chalcopyrite

Thermoluminescence (TL) or natural chalcopyrite (CuFeS₂) obtained from Mosabani Copper Mines shows two glow peaks at 198 and 250°C upon X-irradiation at room temperature. But the quenched sample when X-irradiated shows four glow peaks at 86, 136, 198 and 250°C. The emission spectra of all the glow peaks show a prominent band with a maximum at 566 nm. Both thermal and anomalous fading were observed in quenched samples. Tentative explanations for emission spectra and anomalous fading are given.     

Electrical conductivity of a non-uniformly deformed metal crystal with alloying elements

The effect is considered of non-uniform deformations satisfying the condition |u ||u |, where is the free path length of an electron in the undeformed crystal and, u is the deformation tensor, on the electrical conductivity of a metal crystal with alloying elements. Account is taken of the local change of the dispersion law for conductivity electrons and also of the dependence on the coordinates of the alloying element of the electron scattering cross-section on the alloying element in the non-uniformly deformed crystal. An explicit expression is obtained for the tensor of the effective conductivity, first introduced by Herring and connecting the average volume density of the electrical current with the average electrical field in the crystal. The local electron scattering cross-section on the charged alloying elements is evaluated on the Thomas-Fermi model taking into account the local change of the constant shielding. Account is also taken of the possibility of redistribution of the alloying elements in the field of the deformations. The dependence is found and discussed of the conductivity on the sign of the constant, introduced in the continuous approximation, of the interaction of the alloying element with the deformation field. By way of illustration of the results obtained the simple case of unidimensional deformation is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 70–75, February, 1973.The writers express their gratitude to Yu. V. Kornyushin for useful discussion of this work.     

YAG晶体色心的EPR谱

本文描述了8种YAG样品的室温和77K的EPR谱.从这些谱的参数与光谱的实验数据对照,认为晶体中有三种顺磁性的色心,其中g～2.00和g～1.98两条顺磁谱相应于光谱2×10~4cm~(-1)～3.4×10~4cm~(-1)的吸收带,为YAG基质晶体中的缺陷俘获一个电子构成的电子型缺陷中心;而 g～30.60的顺磁谱线与氧空位和掺杂的金属离子Mg~(2+) 、Cr~(3+)有关,推测为氧空位团或氧空位与金属离子构成的S>1/2的复合顺磁中心缺陷.YAG晶体随着在大气氛中高温退火,氧的进入和金属离子的掺入,造成电子和空间体积的不平衡,从而使晶体色心浓度加大.     

Crystalline properties and colour centres in alkali halide thin films

Abstract

Thin films of KCl, KBr, RbCl have been obtained by thermal evaporation on amorphous substrates with different deposition parameters. The crystalline structure and orientation have been determined, and the films resulted to be policrystals with high uniformity of orientation. Production of colour centres, achieved by irradiation with low-energy electrons, leads to F center concentrations barely observed in large crystals. The colouration kinetics is similar to that in the bulk, and shows after a maximum an exponential decay at high doses because of centre aggregation coupled to thermal effects. The films exhibit a bleaching process of the colour centres at room temperature, whose kinetics depends on the irradiation damage.     

The effect of temperature on the pulsed conductivity of a KCl crystal excited by picosecond electron pulses

This paper discusses the temperature dependence of the pulsed conductivity of a KCl crystal in the interval 12–300K when it is excited by an electron beam (0.2 MeV, 50 ps, 300A/cm²) with a time resolution of 150 ps. It is shown that the electron lifetime is τ<100 ps in the entire interval under consideration, while the conductivity increases with temperature. The experimental results make it possible to obtain the temperature dependences of the effective electron-hole recombination cross section S∼T ^3.5 and the separation probability of genetic pairs. Fiz. Tverd. Tela (St. Petersburg) 41, 429–430 (March 1999)     

Electrochromic colour centres in amorphous tungsten trioxide thin films

Amorphous tungsten trioxide films, investigated by the Raman scattering method, are shown to be composed of a spatial network of tightly bound (WO₆)_n·mH₂O clusters with a large number of terminal oxygen W=O and W-O-W bonds between clusters. The injected electrons in an amorphous tungsten trioxide film are localized in the tungsten 5d orbitals in an axially distorted octahedron, as is shown by ESR analysis. The optical absorption of a coloured amorphous tungsten trioxide film, as has previously been proposed, can be satisfactorily described by an intervalence charge-transfer transition between localized W⁵⁺ and W⁶⁺ states.     

Range-energy relation of electrons in a KCl crystal

The range of electron in KCl 〈100〉 and KCl 〈110〉 crystals in the energy between 30 and 60 keV have been experimentally determined. The data fit an equation of the type, R = kEⁿ. The values of k and n exhibit crystalline orientation dependence.     

The physical behaviour of copper in KCl crystal

Measurements of the absorption and dielectric losses on KCl crystals with high concentration of copper were performed at room and liquid nitrogen temperature. The exciton bands at 383 nm and 375 nm were found as in the case of similar NaCl-Cu samples. After the annealing the bands disappeared, the bands at 226 and 330 nm decreased and the tan-peak at 50 C increased. The interpretation is given on the basis of the existence of Cu-ion agglomerates and their disintegration in octohedral chlorocopper complexes after annealing.The authors wish to express their appreciation to their co-workers K. Dolealová and J. Matouová for careful execution of the experiments.     

Self-trapped excitons perturbed by Na in KCl crystal

The optical absorption and emission induced by electron irradiation of Na⁺-doped KCl was measured and new absorption and emission bands which decay at the same time constant were found and ascribed to the self-trapped exciton perturbed by Na⁺ impurity.     

Thermal conductivity of KCl up to 19 kbar

The pressure dependency of the thermal conductivity of KCl has been measured at room temperature up to 19kbar. The high pressure tool was of the “belt” type and a solid medium was used. The specimen was cylindrical and was heated along its axis. The conductivity was found to increase linearly at a rate of (3·3 ± 0·3) per cent/kbar.