Decay of luminescence and dielectric loss in calcite single crystals irradiated by X-rays

Measurements have been taken on the decay of luminescence and dielectric loss of calcite single crystals after X-ray irradiation. These parameters exhibit similar decay behaviour. In the time range 12–60 min, the decay seems to be connected with the depletion of shallow traps in the forbidden energy region and at longer times, it is apparently due to emptying of comparatively deeper traps.     

Rearrangement of defects in single crystals of cadmium sulfide irradiated with fast electrons

This study exaines CdS single crystals subjected to a special nonalloying treatment, alloyed with copper, and annealed in a cadmium atmosphere. Irradiation of the test specimens by electrons with E 1.2 MeV led to the formation of mobile defects and to decomposition of the original donor-acceptor associates. Over time, the primary radiation defects form secondary defects which act as fast recombination centers responsible for impurity photoconductivity. New donor-acceptor pairs are formed when the irradiated specimens are stored, these pairs being paramagnetic centers. Conclusions are made as to the nature of the secondary radiation defects, which are distributed both in the body of the specimens and near their surface.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 5–9, May, 1988.     

Oscillator strength of electron-type color centers in KCl single crystals irradiated with electrons and protons

The absorption spectra of KCl single crystals irradiated with electrons and protons at energies of 15 and 100 keV and a particle flux ranging from 5×10¹² to 10¹⁵ cm^?2 are investigated. The absorption bands attributed to simple (F, F _a, K) and complex (M, R ₂, R ₄, N) color centers are identified in the spectra. The correlation dependences of the absorption coefficients for M, R ₂, and R ₄ centers on the absorption coefficient of F centers and the correlation dependences of the absorption coefficients for R ₂ and R ₄ centers on the absorption coefficient of M centers are established. The oscillator strengths are calculated for M, R ₂, and R ₄ color centers.     

Orientational dependence of luminescence yield excited by fast electrons in NaCl crystals

An investigation is made of the orientational dependence of the integral luminescence yield when NaCl(T1) single crystals are irradiated by electrons of energy 0.8–2.5 MeV in the direction 100. It is shown that the luminescence yield at small excitation densities depends linearly on the specific ionizational energy losses of the bombarding particles. The ionizational energy losses are calculated for the case when electrons of energy E=1.0 MeV pass through an NaCl single crystal in the direction 100. The minimum observed in the luminescence yield is due to electron capture in canalization conditions and decrease in energy losses. The maximum in the calculated curve at small angles of disorientation is due to the focusing of fast electrons by atomic chains.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 75–79, March, 1979.It remains to thank A. M. Taratin for performing the computer calculations and S. A. Vorob'ev for supervising the work.     

Thermo- and photostimulated luminescence in LiF : Mg,Ti single crystals irradiated by ions and VUV light

A coordinated study of the relaxation of optical absorption induced by vacuum ultraviolet radiation, x-rays, and α-particles, as well as of photo- and thermostimulated luminescence (TSL) of LiF : Mg, Ti crystals (TLD-100) in the 295–750-K interval, has revealed that TSL regions characterized by activation energies E _a = 2.2–2.4 eV and anomalously high frequency factors p ₀ = 10²¹–10²² s^?1 alternate with regions where E _a = 1.5 eV and p ₀ = 10¹²–10¹⁴ s^?1. The relative intensities of the TSL peaks produced by UV illumination (10–17 eV) differ strongly under the conditions of selective photon-induced generation of anion excitons, free electrons and holes, or near-impurity electronic excitations. The latter are responsible for the high efficiency of tunneling radiative (involving titanium centers) or nonradiative (involving hydroxyl ions) recombination. The analysis of TSL peaks of LiF: Mg, Ti and LiF took into account two-step processes, namely, thermal dissociation of three-fluorine F ₃ ^? molecules and recombination of the products of their decay (V _K and V _F centers, H interstices).     

Effect of IR illumination on photocurrent spectra in CdS crystals

Low-temperature near-band-edge photoconductivity (PC) spectra of CdS crystals were studied as a function of IR illumination intensity in the PC quenching interval. The photocurrent quenching by IR light of the PC response profile has been investigated. An analysis of these relationships permitted establishing a direct connection between the r photoconductivity centers and the near-band-edge structure of the spectrum. The effect of “pinning” of majoritycarrier lifetime on the semiconductor surface has been discovered and interpreted. It is proposed that surface-acceptor states in CdS crystals play the part of surface photoconductivity centers. Fiz. Tverd. Tela (St. Petersburg) 41, 1181–1184 (July 1999)     

Variation of the luminescence spectra of spray pyrolyzed CdS with photoexcitation energy

We report that spray pyrolyzed CdS has a luminescence spectrum that dramatically changes with incident photoexcitation energy. Over the photoexcitation range between 1.94 eV and 2.71 eV, the intensity of the 1.22 eV (1020 nm) luminescence line is constant, but that of the 1.55 eV (800 nm) luminescence line first increases, then decreases, and then remains constant. These results are used to measure the 1.55 eV line trap energy of 1.90 eV, and to demonstrate the role of localized carriers in the 1.55 eV line trap cross-section.     

Optical spectra of one-dimensional defect photonic crystals

The effect exerted by defects that represent a local disturbance of the structural periodicity on the band spectrum of a one-dimensional photonic crystal has been investigated. A classification of single defects has been proposed. It has been demonstrated that the position of defect minibands in the band gap of the spectrum of the crystal can be controlled by varying the type of a defect and its location in the crystal structure. The presence of two defects in the structure leads to the formation of two minibands, so that the spacing between the minibands and their intensity depend on the type of defects and on the distance between them.