I.Ya. Fugol

Cathodo-luminescence of rare-gas solid solutions

Abstract Vacuum-ultraviolet luminescence of rare-gas solid solutions of XeAr, XeKr, and KrAr has been measured using excitation by slow electrons. The concentration effect has been studied on the spectra of mixtures at T = 5°K. It is shown that luminescence centers of three types — atomic, molecular and heteroatomic — are formed in the solutions. The bands corresponding to the molecular and heteroatomic centers appear at radiative decay of molecules which are formed in a crystal during excitation. The bands of atomic centers display a fine structure which is due to asymmetric distortion of the sorrounding lattice. Identification of the observed bands has been proposed.

Electronically induced changes in structural properties of solid Kr

Abstract Excitation of the electron subsystem is shown to affect the structural properties of solid Kr at low temperatures. An electronically induced stable point defect formation has been observed. Experiments were performed under irradiation by electrons of subthreshold energy. Defects were detected by means of vacuum ultraviolet luminescence spectroscopy. The results obtained reveal an excited-state mechanism of defect formation when the defect is formed during the lifetime of the excited state. Self-trapping of excitons in the long-lived electronic state 3Σ+u is shown to be a stimulating factor.

Competition and transfer of excimer resonant bindings in rare-gas crystals

Abstract Transfer of two-center excitation (a quasi-molecule with a resonant binding) is considered for rare-gas crystals. The transfer is related to the formation of an additional resonant binding and its competition with an intermolecular one. The transfer probability increases exponentially with the vibrational index of the quasi-molecule. Spectroscopy data supporting the above suggestion are presented.

Effects of exciton-photon interaction and spatial dispersion in xenon crystals

Abstract New data on luminescence from xenon crystals are discussed in terms of the polariton theory, and the treatment of a fine spectrum structure is proposed based on the polariton scattering with participation of some acoustic phonons. The effect of spatial dispersion on transmission and reflection spectra of solid Xe is considered. Verification of the basic parameters of polariton spectrum in xenon is made by comparing calculated and experimental data.

Emission from impurity molecular centres in binary solutions of inert crystals

Abstract The structure of impurity excitations in solid binary solutions XeKr, XeAr, KrAr has been studied using the luminescence vacuum u.v. spectroscopy. Emission from biatomic heteronuclear molecules of inert elements was separated. The existence of two excited states of heteronuclear molecules of different atomic configurations is predicted. The pair potential of inert element interaction in the excited and ground states are analysed and force constants found. The peculiarities of the heteronuclear molecule formation as a function of concentration and temperature for solid binary solutions of inert gases have been discussed.

Stimulation of argon desorption by an oxygen impurity

The influence of an oxygen impurity on the efficiency of desorption of excited atoms and molecules from the surface of crystalline argon is investigated. A significant increase in the yield of desorbed particles is observed at an O2 concentration of 1 at. % in the argon host matrix. It is shown that a xenon impurity does not have a similar effect. Possible mechanisms are proposed for the stimulation of argon desorption by impurity oxygen. One of them may involve the formation of argon microclusters around O− ions near the surface of the crystal. Another mechanism may be due to an increase in the probability of recombination of Ar2+ with an electron on account of the hopping of the negative charge between the O2− and Ar2+ ions.

Dynamics of electronic excitations in YBCO at low temperatures

We present the results of low-temperature optical experiments (absorption and reflection) in visible and middle infrared frequency regions with epitaxial films of copper oxide materials like a Y1Ba2Cu3O6+x. Based on our data and reference data, we consider the anomalous spectral effects in HTSC having no analogy with conventional BCS superconductors: (1) the optical response to superconducting transition at Tc; (2) the spectral weight redistribution induced by chemical doping and temperature; (3) the drastic enhancement of low-temperature photodoping; (4) the long spin-structure relaxation via temperature variations seen in the optical spectra. The thorough analysis of the results obtained is fully compatible with the concept of two-component system of light and heavy carriers (holes), being in dynamical coexistence with each other. The dynamical coexistence of the intraband carriers occurs on the background of strongly correlation interrelation of the heavy quasiparticles with the optical interband (char...

CATHODOLUMINESCENCE OF HIGH-Tc SUPERCONDUCTORS Y–Ba–Cu AND La–Ba–Cu: THE RELATION BETWEEN RADIATION CENTERS AND OXYGEN SUBSYSTEM

Cathodoluminescence spectra of superconducting ceramic Y–Ba–Cu and La–Ba–Cu samples, texturated Y–Ba–Cu films and some classical metals and insulators are investigated. The HTSC multicomponent spectra display two characteristic spectral series of wide bands and narrow lines that are sensitive to the superconducting phase. The luminescence components can be attributed to oxygen radiation centers in the bulk and at the surface of the samples, namely, negative atomic and molecular ions, neutral molecules and oxygen vacancy-based centers.

On the nature of emission bands of self-trapped excitons in solid xenon

Abstract The paper presents the analysis of experimental data on the temperature dependence of luminescence spectra of solid xenon. The mechanisms of exciton self-trapping down to quasi-molecular states under different conditions are discussed. A new treatment of spectral distribution of intensity through quasi-molecular luminescence bands is proposed; according to the treatment, at T

ABSORPTION SPECTROSCOPY OF ELECTRONIC STATES NEAR FERMI LEVEL: TEMPERATURE CHANGES OF SUPERCONDUCTING YBa2Cu3O7−δ FILMS AT Tc

The temperature behavior of the absorption spectra of superconducting YBa2Cu3O7−δ textured films is measured in a 1.5÷3.0 eV energy region with varying temperatures from 25 to 300 K. The spectra are found to be sensitive to a superconducting transition: the temperature-dependent behaviour of absorption at T>Tc undergoes critical changes under the superconducting transition and for T<Tc the spectrum ceases to depend on temperature. The spectra display an exciton maximum in the optical gap Eg=1.95 eV. The spectrum freezing at T<Tc can be explained assuming that the Fermi level is in temperature resonance with a narrow local level which is responsible for a delta-like singularity in the density of states.