Thermoluminescence and optical absorption studies in γ-irradiated KClxBr1–x mixed crystals

Thermoluminescence (TL) and optical absorption measurements have been carried in γ-irradiated KCl, KBr and various compositions of KCl_xBr_1–x mixed crystals as a function of irradiation time and composition. The position of the main glow peak (high temperature peak) and F-band position are found to vary non-linearly with composition, showing a correlation between colour centers and TL. The TL peaks have been analysed by numerical fitting and the trap depths and frequency factors have been calculated for different compositions of the mixed crystals. The thermal ionisation energy of F-centers has been calculated for the mixed crystals and it is found to vary non-linearly with composition. The results obtained in mixed crystals have been discussed in terms of high disorder present in them.     

A thermoluminescence study of Z2-centres in terbium-doped NaCl crystals

Thermoluminescence (TL), optical absorption are used to correlate thermal annealing of Z₂-centres with TL peak occurring around 110 °C in Terbium doped NaCl crystals. The TL glow peak occurring around 190 °C it attributed to the thermal annealing of F-centres. The thermal activation parameters are calculated for both Z₂- and F-centre peaks.     

Thermoluminescence studies in KBrxI1–x mixed crystals

Thermoluminescence (TL) studies have been carried out in KBr, KI, and in different compositions of KBr_xI_1–x mixed crystals as a function of X-irradiation time. The TL glow peaks have been analysed and the trap depths and frequency factors have been calculated for different compositions. The complex TL peaks observed in these crystals were isolated by using thermal cleaning technique. The various glow peaks observed in these crystals were attributed to native impurities, first stage and second stage colour centers and the results have been discussed.     

A study of Z1-centers in γ-irradiated KCl:Ba2+ crystals

The purpose of the paper is to report the optical absorption and thermoluminescence measurements on KCl: Ba²⁺ crystal irradiated with γ-rays. Bleaching in F-band increases the glow peak around 75 °C and suppresses the 125 °C peak. A similar result is observed in preheat treated crystals. When this peak is thermally cleaned, the broadening of the absorption on the prolonged F-bleached crystals is removed. On the basis of these observations, the glow peak at 75 °C is tentatively attributed to Z₁-centers.     

Thermoluminescence of Sr1–xEuxF2 + x Solid Electrolytes

Thermoluminescence (TL) studies have been carried out in different compositions of Sr_1–xEuxF_{2 + x} mixed crystals as a function of X-irradiation time. Three groups of TL glow peaks in the temperature ranges (340, 360 ∼ 370 K), (460 ∼ 475, 540 ∼ 575 K) and (615 ∼ 635, 680 ∼ 720 K) are identified. The growth rates of different glow peaks have been compared with each other to estimate the growth kinetics. The three groups of TL glow peaks are attributed to thermal ionization of radiative impurity centers, different stages of F-centers and other kinds of defect centers such as F-interstitials. The shift in the glow peak maxima is perhaps due to unassociated impurities surrounding F-centers causing a change in configuration. The concentration quenching of TL output due to increased europium is pertinent in Sr_1–xEuxF_{2 + x} mixed system.     

Thermoluminescence studies of Al2O3 crystals doped with Cobalt impurity

Thermoluminescence (TL) studies of cobalt-doped Al₂O₃ crystals irradiated with X-rays have shown that the TL glow curve consists of three peaks at 105, 195 and 260°C. Bleaching, annealing and quanching studies have been performed in order to understand the nature of colour centers responsible for the formation of the three peaks. The values of the fundamental parameters like trap depth and frequency factor are estimated from TL data and the results obtained are discussed.     

Glow Curves of Thermally Pretreated KCl:Mn2+ Crystals

Thermoluminescence studies of KCl crystals doped with 0.5 mole% of Manganese both in “as grown” state and after quenching them from various elevated temperatures indicate that the position of the glow peaks is found to depend upon the state of dispersion of impurity. In quenched crystals two additional peaks one around 130 and other around 215°C are observed. Dipoles near dislocations are suggested to be responsible for 130°C peak and 215°C peak to a complex formed by the associated of one or more Mn²⁺ ions with a single vacancy or an aggregate of vacancies, the complex being situation in the dislocation region.     

Structure sensitivity of relaxation phenomena in NaCl and KCl crystals doped with some divalent impurities [I] ITC-spectra characteristic of the as-cleaved state

ITC spectra of NaCl and KCl crystals doped with europium, lead, and nickel (in a wide concentration range) have been measured at temperatures between 120 and 400 K. It has been shown that the spectra taken for as cleaved samples are usually very rich. The origin and behaviour of the high-temperature peaks (above the IV-dipole peak) have been discussed in frames of the SILLARS theory of Maxwell/Wagner-type polarization effects in heterogeneous dielectrics. It is suggested that the peak positioned near room temperature is related with any type of vacancy rich precipitates formed within otherwise homogeneous crystal lattice. The second peak, positioned at still higher temperatures, is a Maxwell/Wagner effect due to dislocations surrounded by impurity-related imperfections in a fashion of the so called Cottrell atmosphere.     

Glow curves and the emission of BaFCl:Eu2+

Thermoluminescence and the emission of γ-irradiated BaFCl:Eu²⁺ has been studied. A well defined glow peak at 400 K and a shoulder at 480 K are obtained in addition to those obtained as in undoped BaFCl. Thermoluminescence emission has shown a band at about 390 ∼ 400 nm. Additional glow peaks have been attributed to the luminescence centers as caused by europium impurity.     

Effect of Impurity Concentration and Plastic Deformation on Dislocation Density of KCl Crystals

Using the etch pit technique both the distribution and density of dislocations in undeformed and dynamically deformed nominally pure and Sr²⁺ or Pb²⁺ doped KCl crystals are examined. Additionally, the role of specimen geometry in the plastic deformation within the I deformation stage is determined. For all the crystals examined the relationship between screw dislocation density and plastic flow stress obeys the formula τ ⋍ ϱ_sc.^1/2.     

Structure sensitivity of relaxation phenomena in NaCl and KCl crystals doped with some divalent impurities (II) effect of plastic deformation

By studying: 1/the role of dislocations in the origin of the C-ITC-peak in undeformed crystals, 2/ the effect of plastic deformation upon the behaviour of this peak, and 3/ the recovery of the deformation-induced changes of the basic characteristics of this peak (H^C, T_M^C) it has been confirmed that dislocation lines surrounded by the Cottrell-like atmospheres can be considered as polarizable entities related with the high-temperature dielectrical response of as cleaved NaCl and KCl crystals doped with divalent impurities. The Maxwell/Wagner model of polarization effects in heterogeneous dielectrics satisfactory accounts for the majority of the experimental data. The quantitative analysis of the results obtained yields some additional informations concerning the interaction- and motion-parameters of the defects considered.     

Effect of Flux on thermoluminescence in Flux-grown BaFCl crystals

BaFCl crystals have been grown using BaF₂ and BaCl₂ by flux technique. Glow curves, optical absorption, and TL emission spectra of x/r — irradiated crystals are studied. The results have been compared with those BaFCl crystals grown from NaF flux so as to study the effects of flux on these properties. It is found that crystals grown from BaF₂ flux are relatively purer. An additional TL glow peak at 460 K, an optical absorption band at 775 nm and TL emission band at 485 nm have been obtained in the presently grown crystals. The additional glow peak, optical absorption band have been attributed to F(¯F) aggregate centers, whereas the 485 nm TL emission band to impurity centers.     

Glow curves of flux-grown NaMgF3 crystals

Glow curves and optical absorption spectra of X-irradiated flux grown crystals are studied. Two glow peaks at 370, 585 K and three shoulders at 420, 540 and 610 K are obtained. Optical absorption studies reveal two absorption bands at 405 and 475 nm and a well defined peak at 295 nm. Room temperature annealing and bleaching studies have suggested that the glow peaks at 370 and 585 K may correspond to impurities and F-centers of 295 nm band respectively. The other shoulders at 420, 540 and 610 K are attributed to other F-aggregate centers. The glow peaks are analysed using first order kinetics.     

Low temperature TL glow curves in KBrxI1-x mixed crystals

Thermoluminescence (TL) glow curves were recorded in KBr, KI and in different compositions of KBr_xI_1-x mixed crystals at LNT. For this a cryostat has been designed and fabricated. The glow peaks observed in these crystals have been attributed to differnent colour centers.     

Deformation Modes and Structure Evolution in Laser‐Shock‐Loaded Molybdenum Single Crystals of High Purity

This paper reports on the microstructural changes occurring within molybdenum single crystals after shock treatment with an excimer laser‐system in a confined ablation mode with different number of impacts. Using different complementary investigation methods (optical microscopy, scanning electron microscopy and transmission electron microscopy) it is found that slip and twinning are active modes of deformation during the shock‐induced plastic deformation. After laser treatment with a single laser pulse slip bands on {112} planes containing several microscopic twins are the dominating microstructural feature, whereas further laser‐shock‐processing leads to the formation of a homogeneous arrangement of screw dislocations, tangles and loops. Deformation modes and microstructure in laser shocked samples prove to be quite similar to those of explosive shocked specimens although the laser‐induced peak pressure is about an order of magnitude lower than that during explosive loading.It is shown that the laser shock‐induced hardening increases with increasing number of impacts in the range from 1 to 6 impacts. This shock‐induced strengthening is correlated with the overall dislocation density.     

Low-temperature Thermoluminescence Glow Curves in NaCl Crystals Doped with Yttrium

Thermoluminescence glow curves were recorded in undoped and yttrium-doped NaCl crystals X-irradiated at liquid nitrogen temperature (LNT). An attempt is made to assign the glow peaks observed to different centres such as V_k-centres and yttrium related centres etc.     

The coloration effect in KCl: Eu2+ crystals γ-irradiated at 200 K

The formation of colour centers at 200 K in γ-irradiated KCl crystals doped with Eu²⁺ ions in a wide concentration range is studied by optical absorption, EPR, and ITC method. The EPR and ITC measurements reveal the drastic decrease of concentration of isolated europium dipoles induced by irradiation at 200 K. Moreover, no correlation between concentration changes of colour centers and Eu²⁺ dipoles induced by irradiation and postirradiated annealing has been found. The results obtained are explained by radiation stimulated aggregation of Eu²⁺ dipoles into small clusters at 200 K.     

Effect of Grinding on the Low Temperature Photoluminescence of Certain Molecular Crystals

The wavelengths of the vibronic peaks of the low temperature photoluminescence of anthracene, phenanthrene, benzophenone and phthalic acid crystals do not change considerably, but their relative intensity changes significantly with grinding. The dislocations may change both the absorption coefficient and absorption spectra of the crystals, hence the photoluminescence emission may be affected by the grinding.     

The role of Mg2+-V-dipoles: In the thermoluminescence of LiF2:Mg single crystal

The thermoluminescence and radiation or thermally induced changes of the concentration of magnesium dipoles have been studied in LiF:Mg²⁺ crystal grown in an inert atmosphere. The evolution of the TL spectrum with γ-radiation dose shows that the glow peaks observed at the beginning of irradiation decrease at high doses whereas new peaks, positioned at higher temperatures, appeare. Moreover, it has been found that the thermally induced recovery of the dopant dipoles, destroyed during the irradiation, strongly depends on the dose applied. The recovery curves obtained for a fixed irradiation dose dose not exhibit thermal annealing steps at temperatures, at which glow peaks occur. Further, the number of the recovered magnesium dipoles is not correlated with the quantity of light emitted during heating the irradiated crystal what is expected in respect to some of the previously proposed models. On the basis of results obtained it is proposed that the decay of the magnesium dipoles is mainly due to the dopant aggregation induced by the γ-radiation. The role of the magnesium ions in thermoluminescent processes is discussed.     

A study of complex glow curves of Quenched NaCl:Ca crystals

Glow curves of the thermally pretreated NaCl:Ca crystals are recorded and are found to be complex in nature. The complex glow curve is analysed using thermal cleaning technique and the trap parameters are calculated by various methods. The glow peaks have been tentatively attributed to impurity and various types of colour centers.