Luminescence properties of calcium-iodide crystals

The effect of the conditions of preparation, temperature, and the action of x rays on the luminescence properties of calcium-iodide scintillation crystals is investigated. On the basis of the results of a study of the spectral characteristics of CaI₂ and CaI₂:H₂ crystals for optical and x-ray excitation in the temperature range 90–400 K, also taking into account the results of a study of the luminescence properties of CaI₂ crystals activated by Cl⁻, Br⁻, OH⁻, and Ca²⁺ impurities, it is suggested that the 236-nm band observed in the excitation spectra of crystals of calcium iodide may be caused by an uncontrollable hydrogen impurity. The luminescence of these crystals with maximum at 395 nm is ascribed to radiative recombination of excitons trapped at H⁻ ions. Zh. Tekh. Fiz. 69, 135–136 (January 1999)     

Electrical properties of plastically deformed silicon crystals

The influence of the nature of the interaction of deformation and impurity defects on the scattering of majority carriers is investigated in silicon single crystals. Fiz. Tverd. Tela (St. Petersburg) 40, 1816–1817 (October 1998)     

Diffusion properties of plastically deformed silicon crystals

The effect of dislocations generated by electroplastic strain on the electric-field-driven transport of impurity atoms of indium in single crystals of P-silicon is investigated experimentally. It is shown that when electrodiffusion of indium and strain are induced simultaneously, the impurity ions are preferentially dragged towards the anode. Fiz. Tverd. Tela (St. Petersburg) 41, 1028–1029 (June 1999)     

Luminescence and ESR detected hydrogen related electron traps in yellow-colored CaO crystals

Abstract

Electron spin resonance of the off-center H^2- ions replacing oxygen in additively colored CaO crystals has been investigated. Electron tunneling in F… H^? pairs is essential in photoconversion and thermoluminescence of CaO at low temperatures.     

Luminescence properties of Ce-doped oxyorthosilicate nanophosphors and single crystals

In this work we investigate and compare the thermoluminescence (TL) and related luminescent properties of cerium-doped Lu₂SiO₅ (LSO), Gd₂SiO₅ (GSO), and Y₂SiO₅ (YSO) nanophosphors prepared by solution combustion synthesis (SCS) to the properties of their single crystal counterparts. Photoluminescence emission and excitation spectra were obtained for comparison with TL and radioluminescence (RL) emission bands. We then compared the structure and intensity of TL curves, RL intensity, and afterglow at room temperature and investigated the trapped charge stability (revealed by TL). The results showed that the SCS technique is capable of producing scintillating materials with less afterglow and RL output comparable to single crystals. The nanophosphor samples also showed lower TL intensities than their single crystal counterparts, which points to a lower concentration of trapping centers. These results demonstrate the potential of nanophosphors produced by SCS for use as scintillators.     

Cathodoluminescence in deformed MgO crystals

The corrected cathodoluminescence (CL) emission spectrum for undeformed MgO in the wavelength range 300–650nm consists of two overlapping bands with peaks at 425 nm (2.92 eV) and 488 nm (2.54 eV). After deformation one broad band at 466 nm (2.66 eV) of much higher intensity is observed. In the near IR part of the spectrum a further broad band occurs, consisting of a number of unresolved peaks the strongest of which is at 726 nm (1.71 eV). This band is unaffected by deformation and is thought to be due to iron impurities. Panchromatic and monochromatic SEM micrographs show that the enhanced 466 nm band luminescence comes from the slipped planes of the crystal. Shape analysis of the 466 nm emission band showed that it is a Gaussian form around the intensity maximum with an exponential high energy tail.     

Luminescence of mercuric iodide crystals

Low-temperature (4.2–130 K) photoluminescence spectra of HgI₂ crystals have been measured in the 540–700 nm region. An analysis of the characteristics (intensity vs temperature and excitation power relations, afterglow times, excitation spectra) of the 560, 620, and 635 nm emission bands suggests the following assignments: the 560 nm band is due to radiative annihilation of excitons bound to mercury vacancies, and the “red” emission originates from recombination of free (620 nm) and donor-localized (635 nm) electrons with a hole-filled acceptor level. The energies of the corresponding donor and acceptor levels have been estimated. New emission bands at 540, 545, and 575 nm have been discovered, and their origin discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 67–73 (January 1997)     

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.     

Cathodoluminescence from deformed doped MgO crystals

The cathodoluminescence (CL) from indented Fe doped MgO single crystals has been studied with the scanning electron microscope and the results have been compared with the CL from undoped crystals. As in the undoped crystals, the iron doped crystals show in the deformed regions an enhanced luminescence emission but it has been found that iron acts as a quencher of luminescence. The results indicate that in the blue emission of the deformed crystals there is not a noticeable contribution of iron. From the evolution of CL with the irradiation time in the electron microscope it is concluded that the total Fe content influences the CL emission more than the Fe³⁺ content.     

Red luminescence from deformed MgO crystals

Annealing of deformed MgO single crystals at temperatures above 400°C causes several changes in the excitation and emission photoluminescence spectra. In particular, an emission band at 695 nm associated with the deformation damage appears at 400°C. Other changes in the temperature range 400–1300°C which show the composite character of the blue emission are described.     

The influence of rest on the micromechanical properties of preliminarily deformed MgO single crystals

The influence of a prolonged rest at room temperature on the activity of acoustic emission upon microindentation of preliminarily deformed MgO single crystals is investigated. It is found that the number of acoustic emission signals after the specimens have rested increases at low loads P (～50 g) applied to an indenter and decreases at high loads P (～200 g). The change observed in the activity of acoustic emission depends on the degree of preliminary deformation. It is assumed that the observed effects are associated with the difference between the sources of acoustic pulses: the main contribution to the activity of acoustic emission comes from the breakaway of dislocation pileups at low loads P and from the formation of microcracks and macrocracks at high loads.     

Internal friction of deformed zinc single crystals

Zinc single crystals with the side in a (0001) basal plane were elongated and the internal friction measurements were carried out as a function of temperature in the mode of a flexural vibration. Two relaxation peaks were observed to appear: one at around 500°K and the other at about 570°K. Each activation energy was obtained 0.70±0.08eV and 1.01±0.06eV, respectively, by the peak shift method. The experimental results were discussed in terms of dislocations in pyramidal slip system {$\text{11}$22} 〈11$\text{2}$3〉 and twinning dislocations in the planes {$\text{1}$012} 〈10$\text{1}$1〉, respectively.