Sh− Defects in Potassium Chloride Crystals

The Hartree-Fock-Rutane method in a semi-empirical version of the average neglect of differential overlapping has been used for calculation of the electronic structure and the spectroscopic properties of the SH^? ion in potassium chloride. The orientation of impurity defect, shifts of surrounding ions, energies of optical absorption, ratios of harmonic frequencies and the first derivatives of dipole moment function of ions in free state and in a crystal were determined. The obtained values are in a good agreement with experimentally measured data.     

Neutralization of H− ions in collisions with fast, multiply charged ions

The neutralization of H⁻ ions in collisions with fast, multiply charged ions is considered in the parameter region where the Born approximation applies. An analytical formula is obtained for the H⁻ neutralization cross section in such collisions. Zh. Tekh. Fiz. 69, 1–4 (July 1999)     

Thermally Stimulated Electron–Hole and Ionic Processes in Zinc Oxide Crystals

The principal results of the investigation of thermally stimulated electron–hole and ionic processes in hydrothermal and gas-phase ZnO single crystals preexcited at low temperatures, based on simultaneous study of photo-EPR and thermoluminescence (TL), are presented. The nature of the traps determining the TL peaks at 17, 24, 40, 53, 90–110, 140–150, and 160–200 K is discussed. In particular, it has been established that the lithium paramagnetic centers (Li_Zn ⁺–O^I) play the role of hole traps in ZnO giving green and red TL in the temperature range 160–200 K and, in the case of association with small-sized donors, also TL in the temperature range 90–110 K. The other traps are electronic in character, and in the presence of acceptor lithium in the crystals, they form yellow-orange TL. Optical quenching of TL has been evaluated, and it has been found that there is a difference E 0.75 eV between the thermal and optical energies of ionization of lithium acceptors. Irreversible ionic processes associated with the healing of cationic vacancies at T 360–420 K have been revealed.     

Loss of electrons by fast H− ions in gases

The characteristic angles and cross sections for a (\mathop 1^- 0) + (\mathop 1^- 1)(\mathop 1\limits^ - 0) + (\mathop 1\limits^ - 1) reaction in which H⁻ atoms with an energy of 0.1–10 000 MeV lose electrons when scattered on C, N, or O atoms were calculated for the relativistic case of the Bethe scattering theory. The cross sections for N₂, O₂, and CO₂ molecular targets were obtained using the additivity rule. The results presented are compared with known experimental and theoretical data.     

Reflection Spectra of Single Crystals of La2CuO4−x ‐Type Metal‐Oxide Compounds

We have investigated the reflection spectra in polarized light at 80 and 295 K in an energy region of 1.0–4.8 eV for the single crystals of ternary and quaternary copperoxide systems with the participation of rareearth elements (La₂CuO_4–x , LaCuO₄, Pr₂CuO_4–x , GdBa₂Cu₃O_7–x , and LaSrCaCuO).     

Theoretical study of LiCl− and LiBr− molecular ions

The molecular structures and spectroscopic constants of the ground electronic states of LiCl^? and LiBr^? are investigated with the coupled-cluster method. To improve the accuracy of our calculations, we have employed the extrapolation schemes as well as corrections of the core–valence correlation and scalar relativistic effect. The equilibrium parameters, potential energy curves, force constants, vibrational energy levels and spectroscopic parameters of both molecular ions are derived, in which those of LiBr^? are reported for the first time. The electron affinities and vertical detachment energies of neutral and anionic LiCl and LiBr are also evaluated.     

OH− dipole reorientability in hydroxyapatites: Effect of tunnel size

A study of calcium phosphate hydroxyapatite with the thermally stimulated currents methods (TSC) has led to the conclusion that the reorientable dipoles responsible for the dielectric properties measured are the structural OH⁻ ions in the “tunnels”. The co-operative motions along chains of these dipoles have been followed by the identification and determination of compensation phenomena at T_c = 212°C and 356°C. These phenomena correspond to physical events characterized by co-operative motions, such as the monoclinic-to-hexagonal phase transition observed in several apatites. Even in a material in which the higher temperature phase is frozen in at a lower temperature (e.g. by defects or by quenching), the TSC method can reveal the onset of those co-operative dipole reorientations which would otherwise produce a phase transition.An effect of the “tunnel” size and environment of OH⁻ dipole reorientation movements has been investigated with two additional hydroxyapatites, strontium phosphate hydroxyapatite, Sr₁₀(PO₄)₆OH₂, and calcium arsenate hydroxyapatite, Ca₁₀(AsO₄)₆OH₂. “Tunnel size” is here defined as the distance from the center (6, axis) to the ion center less the ion radius. The larger tunnel sizes led to lower compensation temperatures.     

Combination transitions due to stretching and librations of OH⁻ ions in LiNbO₃

A new absorption band has been detected at 4009 cm?1 in stoichiometric LiNbO? single crystals. Based on present and earlier experiments and recent calculations, this band has been assigned as a combination transition involving the OH stretching and an OH librational mode. The librational mode participating in this combination is of lower fundamental frequency than that contributing to the combination band at 4415 cm1 observed by Gr?ne and Kapphan [J. Phys. Condens. Matter 7, 3051 (1995)].     

Spin-orbit coupling constant and <r −3> in transuranic ions

The spin-orbit coupling parameter ζ, the quantum average <r ^?3>, and binding energy ? E for atomic number Z = 92, 94, 96 and net ionic charge approximately 1 and 5, have been calculated for the 5f electrons. The potential assumed in the one-electron wave function calculation is that given by the Thomas-Fermi model of a positive ion.

It is shown that the ratio ζ/<r ^?3> is fairly insensitive to changes in the surroundings of the ion, and can be used for estimating one of the parameters with the experimental value of the other.

The 5g electrons are shown to be effectively free in the considered range of Z and n.

The behaviour of the wave function as a function of n and Z is discussed.     

Negative Ca− and Ba− ions of large radius on the surface and in the volume of liquid helium

Negative Ca⁻ and Ba⁻ ions of large radii on the surface of and in bulk liquid helium have been studied. Our results indicate that these ions are adsorbed on the helium surface. Ions on free liquid helium surfaces have not been studied previously because it was thought impossible to confine them on the surface. Ca⁻ and Ba⁻ ions have very low binding energies, therefore, like electrons, they form a bubble of large radius in bulk helium, whose energy is higher than on the surface. The behavior of ions on the surface exhibits a number of previously unknown features owing to their large masses and strong localization in the horizontal plane. Even in the absence of confining electric field, a hole is formed under an ion due to the polarization attraction between the liquid helium and the charged ion. This hole formation reduces the ion mobility by several orders of magnitude and increases its effective mass severalfold. The critical density of electrons and ions is approximately the same on the surfaces of thin and thick helium films. Zh. éksp. Teor. Fiz. 115, 593–604 (February 1999)     

Uncommon temperature dependence of the rotational motion of OH− centers in NaCl

Abstract

The correlation time τ_D of the rotational motion of OH^? centers in NaCl was studied for two different OH^?-concentrations (44 ppm and 220 ppm) between 0.5 K and 16 K by ²³Na nuclear spin relaxation measurements. The correlation time in the sample containing 44 ppm OH^? is given by phonon-assisted tunneling of isolated defects, whereas the OH^?-motion in the sample containing 220 ppm can be described by a coupled ensemble of quantum mechanical hindered rotators below a critical temperature which is determined by the strength of the interaction between the OH^? dipoles.     

Spectroscopic studies of Pr3+ ions in KPrxY1−xP4O12

Emission and absorption spectra of KPr_xY_1−xP₄O₁₂ were investigated at 40, 77 and 300 K and the resulting energy level diagram of Pr³⁺ in KPrP₄O₁₂ was deduced. On the basis of the Judd-Ofelt theory the optical absorption intensities of KPrP₄O₁₂ were examined and the three phenomenological parameters Ω_t determined. A calculation of the radiative decay rates of the KPrP₄O₁₂ system as well as the fluorescence branching ratios and the emission cross sections was made and the theoretical values were compared with the measured data. The results allow us to predict the laser parameters of these crystals.     

Sonochemical nitrogen fixation for the generation of NO2− and NO3− ions under high-powered ultrasound in aqueous medium

Sonochemical species such as nitrite (NO₂⁻) and nitrate (NO₃⁻) were detected in ultrapure aqueous medium with 28 kHz low frequency ultrasound (US) in the range of 200–1200 W output power. The concentration of their anionic ions monitored with a high-performance liquid chromatography increased with increasing US power especially under air atmosphere. When the generation of NO₂⁻ and NO₃⁻ ions under US exposure was investigated for N₂, O₂ and Ar-bubbled solutions, no trace of NO₂⁻ was observed while NO₃⁻ was slightly generated. Under air atmosphere, the concentration of dissolved oxygen in the aqueous medium increased especially when 1200 W power was used. In addition, the bulk pH shifted towards the acidic side with an increase in exposure time, which indicated that NO₂⁻ was formed. The formation of oxidizing species under 28 kHz low frequency ultrasonic treatment was confirmed with an absorption spectrum which was dominated by two maxima peaks at 288 nm and 352 nm representing triiodide I₃⁻ anion.     

Modulation Instability in Biased Photorefractive-Photovoltaic Crystals

We show the modulation instability of broad optical beams in biased photorefractive-photovoltaic crystals understeady-state conditions. This modulation instability growth rate depends on the external bias tield, the bulkphotovoltaic effect, and the ratio of the optical beam intensity to that of the dark irradiance. Under appropriateconditions, this modulation instability growth rate is the modulation instability growth rate studied previouslyin biased photorefractive-nonphotovoltaic crystals, and the modulation instability growth rate in open- andclosed-circuit photorefractive-photovoltaic crystals can be predicted.     

Valence state of manganese ions in the La1−α BiLaβMnLa1−δ OLa3±γ ceramics

The valence state of the Mn ions in ceramic samples of the La_1?α BiLa_βMnLa_1?δ OLa_3±γ composition (LBMO) has been studied using the X-ray photoelectron spectroscopy. The presence of Mn³⁺ and Mn⁴⁺ ions in these compounds has been shown. The relative content Mn³⁺/Mn⁴⁺ has been determined by means of fitting the experimental Mn 2p spectra by the superposition of theoretical spectra of Mn³⁺ and Mn⁴⁺ ions. The elemental composition of the samples has been determined by the X-ray photoelectron spectroscopy and electron probe microanalysis. It has been established that the relative content of Mn⁴⁺ ions correlates with parameter δ, which characterizes the deviation of the actual elemental composition of the La_1?α BiLa_βMnLa_1?δ OLa_3±γ ceramics from stoichiometry La_{1 ? x} Bi _x MnO₃.     

Optical properties of (F2 +) H centers in NaCl:OH− crystals

Abstract

In this work we present new data on the formation and destruction of the laser active (F₂ ⁺)     

The migration of Mn2+ ions in Cd1−xMnxS nanocrystals: Thermal annealing control

This work reports evidence of the induced migration of Mn²⁺ ions in Cd_(1?x)Mn_xS nanocrystals (NCs) by selecting a specific thermal treatment for each sample. The growth and characterization of these magnetic dots were investigated by atomic force microscopy (AFM), optical absorption (OA), and electronic paramagnetic resonance (EPR) techniques. The comparison of experimental and simulated EPR spectra confirms the incorporation of Mn²⁺ ions both in the core and at the dot surface regions. The thermal treatment of a magnetic sample, via selected annealing temperature and/or time, affects the fine and hyperfine interaction constants which modify the shape and the intensity of the EPR transition spectrum. The identification of these changes has allowed tracing the magnetic ion migration from core to surface regions of a dot as well as inferring the local density of the magnetic impurity ions.     

Spatially Inhomogeneous Gain Modification in Photonic Crystals

The electric and magnetic energy distributions in photonic crystals （PC） are calculated by using the plane wave expansion （PWE） method. Even though the total electric and magnetic energy in each unit cell of photonic crystals are equal to each other, the ratio of electric and magnetic energy densities varies depending on the local position. Based on Fermi＇s golden rule, the optical gain is analysed in the full quantum framework that takes the nonuniform energy density ratio into account. This nonuniform energy density ratio in photonic crystals, defined in an equal form as gain modification factor, leads to spatially inhomogeneous modification of optical gain. Results reported in the paper provide a new perspective for analysing gain characteristics, as well as the lasing properties, in photonic crystals.