Luminescence and the migration of the energy of electron excitation in stilbene crystals

The dependence of the quantum luminescence yields on the concentration of impurities in crystals of stilbene with admixtures of anthracene is investigated. On the basis of the experimental results a diffusion length is calculated for the excitons as well as the probability of their capture by impurity molecules.     

Hole-electron mechanism of F-H pair generation in RbCl crystals with impurity electron traps

Production of F, Cl ₃ ⁻ , Ag⁰, and Tl⁰ centers in RbCl:Ag and RbCl:Tl crystals by photons having energies ranging from 5 to 10 eV has been studied at 295 and 180 K. It is shown that creation of near-impurity excitations is accompanied by formation of F centers localized in the vicinity of Ag⁺ and Tl⁺ ions. F centers are produced in direct optical generation of self-trapped excitons. In addition to the well-known mechanism of F-H pair production in nonradiative recombination of electrons with self-trapped holes, a hole-electron process has been revealed for the first time to operate in RbCl:Ag having deep electron traps. By this mechanism, F-H pairs appear in the following sequence of stages: thermally stimulated unfreezing of hopping diffusion of self-trapped holes (V _K centers), tunneling electron transfer from Ag⁰ to the approaching V _K centers, and subsequent nonradiative decay of triplet self-trapped excitons near Ag⁺ ions. Fiz. Tverd. Tela (St. Petersburg) 40, 1238–1245 (July 1998)     

Luminescence and biexcitons in nitrogen crystals

We have studied vacuum ultraviolet luminescence spectra of nitrogen crystals at different excitation densities. Forbidden transitions from three singlet states $\text{a}{}^1\text{Π}{}_{\mathrm{g}}\text{, a'}{}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{?}}\text{,}\text{and}\text{w}{}^1\text{Δ}{}_{\mathrm{u}}$, have been observed. A non-linear dependence of luminecence of the excitation intensity has been found. A characteristic feature of the singlet transitions observed is a fine structure of vibronic bands. The luminescence spectra of pure crystalline nitrogen is compared with those of impurity luminescence of solid solutions N₂—Ar. The nature of singlet luminescence of nitrogen crystals is discussed proceeding from the two-particle radiation mechanism.     

Electron and hole traps in N-GaAs crystals

Deep traps were measured and their electronic and optical properties were determined by junction capacitance techniques in n-GaAs crystals grown by different methods. Four electron-traps and four hole-traps were detected. An electron trap was not observed in LPE wafers. A hole trap at 0.45 eV above the top of the valence band was detected in all wafers measured here.     

Luminescence decay in AgCl crystals

The kinetics of luminescence decay of single crystal plates of AgCl was measured at the temperature of liquid nitrogen. Luminescence decay first takes place (fort≦2·5× ×10^?3 sec) according to a hyperbole and then according to an exponential. The constantsa anda of the hyperbolic andt of the exponential dependence were measured for different intensity of the exciting radiation in normal and deformed samples and in samples irradiated withb-particles during measurement.     

ELectron traps in silver chloride crystals

The photoelectret state has been examined for AgCl crystals after treatment with heat and light; it is found that there are shallow electron trapping levels, whose ionization energy ₁ is about 0.2 eV and whose concentration n₁ is about 10¹⁷ cm^–3. These appear to be due to inherent defects in the lattice of AgCl.     

Positron traps in radiation-colored KCl crystals

We studied the effect of thermal and radiation annealing of defects and optical deexcitation with Flight on the angular distribution of annihilation radiation of KCl crystals irradiated with electrons and protons. The results show that divacancies are the main type of positron traps in irradiated KCl crystals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 55–61, November, 1978.     

Luminescence kinetics of dipolar excitons in circular traps

A detailed investigation of multiband superconductivity and Leggett’s mode in the Mg_1?x Al_xB₂ (0 ≤ x ≤ 0.45) system was carried out using tunneling and Andreev spectroscopy. Temperature dependences of superconducting gaps Δ_σ and Δ_π and their variation upon the degree of disorder and the Al concentration were studied. The dependence of the Leggett’s mode energy ε₀ upon the values of the gaps Δ_σ and Δ_π has been derived.     

Luminescence centres in pure AgCl crystals

The temperature dependence and the influence of pressure on band width of blue-green luminescence were measured in pure AgCl crystals. The comparison of results obtained with other published data support the existence of two luminescence centres (in the temperature ranges between 130–160°K and between 20–30°K).     

Shallow traps in pure KTaO 3 crystals

We made Thermally Stimulated Conductivity (TSC), Thermoluminescence (TL) and Electron Spin Resonance (ESR) measurements on single crystals of potassium tantalate in the temperature range 4.2-290 v K. We revealed two sorts of O m shallow hole centers which are responsible for Photoconductivity (PC) and Photoluminescence (PL) enhancement. Both O m centers were identified by their ESR spectra. We show that these centers serve as radiative electron-hole recombination centers. The measurements of TSC and TL after UV irradiation revealed several glow peaks at temperatures 18-30 v K and 65-70 v K. Both TSC and TL are attributed to the thermal ionization of the same shallow donor centers related with oxygen vacancies. Experimental data were treated in a simple one-trap/one-recombination center model, which takes into account the presence of "thermally disconnected" deep electron traps.     

Luminescence and ESR studies of defects in hydrogenated amorphous silicon

New experimental information on luminescence and light induced ESR (LESR) in hydrogenated amorphous silicon is described. We demonstrate that the two experiments involve identical recombination transitions, and identify two separate processes. One process involves defect states, and from the doping dependence of LESR we deduce that the electronically active defects are dangling bonds with positive electronic correlation energy.