Electron-hole Process Research Articles

Thermally Stimulated Luminescence and Exoelectron Emission Mechanism of the 430 K (D') Dosimetric Peak of a-Al2O3

Several a-Al2O3 samples were studied in order to determine the mechanism of electron-hole processes of the 430 K (D') thermoluminescence (TL) and thermally stimulated exoelectron emission (TSEE) dosimetric peak. Single crystals prepared in highly reducing conditions were treated in different atmospheres (reducing/oxidising) and their optical absorption (after isochronous annealing), fluorescence and TL properties were investigated. From these results an electron trap is suggested for the 430 K peak which is in contradiction to some data taken from the literature: this problem is then discussed. Pure and Th4+ doped a-Al2O3 powders were studied by TL methods regarding doping concentration and preparation conditions. In this way the role of aluminium vacancies is proved. Considering these new results, literature data and different hypotheses, the possible nature of the trap is discussed.

The relativistic layer-resolved electronic structure and photoemission of the adsorbate system Xe/Pt(111)

For the ( square root 3* square root 3)R30 degrees commensurate physisorption system Xe/Pt(111), the K/sub //-/, layer- and double-group-symmetry-resolved density of states (LDOS) as well as spin-resolved normal photoemission spectra for circularly and linearly polarized light have been calculated by means of a fully relativistic Green function formalism. Comparison with the LDOS obtained for an isolated Xe monolayer shows that the mj splitting of the 5ps2/-derived states of the Xe adsorbate is almost exclusively due to the lateral interaction within the Xe layer. In contrast. Pt derived features are strongly determined by the Xe overlayer via 'surface umklapp': firstly, electronic states localized in the two topmost Pt monolayers; and secondly, photoemission features originating from umklapped Pt bulk initial states. For circularly polarized light, we obtain very good agreement with experiment with regard to peak positions and sign of the spin polarization. Substantial discrepancies in absolute polarization values are ascribed to Auger-like electron-hole processes and call for an extension of our photoemission theory to incorporate these additional excitation channels. For linearly s-polarized light, the calculated spin polarization spectra depend very strongly on the lateral position of the Xe layer relative to the substrate.

Thermoluminescent and Exoemission Properties of New High-Sensitivity TLD a-Al2O3:C Crystals

To determine the mechanisms of the electron-hole processes in a-Al2O3:C crystals, characteristics of their thermo- and photo-stimulated exoelectron emission (TSEE, PSEE) and luminescence have been studied. It is shown that the emission of F+ centres takes place with the temperature shift relative to the emission of F centres, and the hole-induced TSEE takes place synchronously with the emission of F centres. The electron energy distribution parameters at PSEE do not depend on the energy of stimulating light photons, which testifies to thermalisation of the released holes before their recombination. Parameters determined for doped anion-deficient corundum crystals are considered within the framework of the two-stage Auger process model.

Thermoluminescent and Exoemission Properties of New High-Sensitivity TLD a-Al2O3:C Crystals

Abstract To determine the mechanisms of the electron-hole processes in a-Al2O3:C crystals, characteristics of their thermo- and photo-stimulated exoelectron emission (TSEE, PSEE) and luminescence have been studied. It is shown that the emission of F+ centres takes place with the temperature shift relative to the emission of F centres, and the hole-induced TSEE takes place synchronously with the emission of F centres. The electron energy distribution parameters at PSEE do not depend on the energy of stimulating light photons, which testifies to thermalisation of the released holes before their recombination. Parameters determined for doped anion-deficient corundum crystals are considered within the framework of the two-stage Auger process model.

Luminescence and epr of electron-irradiated zinc oxide single crystals

Zinc oxide is used extensively in engineering and its properties depend essentially on the presence of point defects in the crystals [I]. A common way of forming defects in zinc oxide, especially intrinsic point defects, is by irradiating the crystals with fast particles, particularly electrons. Even though many such studies have been carried out [2-11] many questions pertaining to the microstructure and role of defect formation on electron-hole processes of charge transfer remained mainly unresolved [I].

On galvanomagnetic size effects in metals

The importance of open electron trajectories formed by specular reflections of charge carriers by the sample boundary to the metal electric conductivities in the strong magnetic fieldH is analyzed. It is shown that the electric conductivity of the near-surface layerσskin is rather sensitive to the state of the conductor surface. The electron-hole Umklapp processes during the surface scattering of charge carriers do not change the dependenceσskin(H), while skipping from the closed Fermi surface section to the open one is able to affectσskin essentially only in bulk samples. The method is proposed to restore the indicatrix of conduction electron scattering by the sample boundary through an experimental investigation of the Sondheimer effect and the static skin effect.

Semiconductor properties and general applications op optical ceramics

Abstract The electron and hole processes in transparent ferroelectric ceramics (TFC) are considered. The basic concepts about the defects and their relation to the electric conductivity in TPC are analyzed. Results of the studies of electrical properties of the surface and specific features of hologram forming are presented. The basic applications of electron-hole processes in TPC are discussed.

Calculation of the kinetics of pulsed luminescence by means of an analog computer

Electronic analog computers are successfully used to solve kinetic equations in, for example, the radiation physics of crystals [1] and chemical kinetics [2]. They have been used in a number of calculations of the kinetic constants in the equations that describe thermoluminescence [3–7]. However, it must be borne in mind that the numerical values found in these studies are relative in nature, since they are not connected to the parameters of a definite substance. The aim of the present work is to see if the mathematical equations give an adequate description of the physical processes in a definite material and to make calculations with an analog computer of the capture and recombination probabilities and effective cross sections of the corresponding electron centers. Concretely, an MN-18 analog computer was used to analyze the kinetics of pulsed luminescence of the phosphor KI-T1 (1 mole % T1) in the temperature range 200–300°K. It was established earlier that at these temperatures the electron-hole processes in the crystal have a number of features that lead to a change in the amplitude-time characteristics of the luminescence. For example, it is necessary to take into account the localization of free holes at V2 centers and the thermal instability of the activator hole centers above 290°K, which influences the luminescence intensity [11]. On the other hand, thermal destruction of the electron T10 centers leads to delayed luminescence [10].

Nonlinear optical properties of InSb: Hot-electron effects

At high-power densities (\ensuremath{\gtrsim} 2 MW/${\mathrm{cm}}^{2}$) the temporal dependence of transmitted 10.6-\ensuremath{\mu}m pulses in InSb shows strong pump-depletion effects. The phenomena are on a 30-nsec time scale and are interpreted as due to hot-electronic kinetics and electron-hole excitation processes. A model calculation employing rate constants from independent measurements reported in the literature yields good agreement with the experimental time evolution of the transmitted signal.

Localized states and electron-hole processes in BiI3 crystals

Results of the photopolarization and photoluminescence investigations in BiI3 single crystals are presented. A model of electron processes is considered, which is connected with localized states caused by the presence of nonstoichiometric Bi impurities. [Russian Text Ignored]