Thermoluminescence and Optical Absorption Studies of Z1 Centers in KCI Crystals Doped with Praseodymium

Thermoluminescence (TL) of Pr-doped KCI is studied. The influence of pre-heat treatment and optical bleaching of the glow curves and the production of Z₁ centers are discussed. The glow curves of KCI containing 1062 ppm of praseodymium (Pr) shows one shoulder at 365 K (T₁) and two peaks around 408 K (T₂) and 443 K (T₃), respectively. Bleaching of X-irradiated crystals shows that the peak T₂ is enhanced whereas other two (T₁, T₃) get suppressed. Optical absorption studies of the crystals before and after F-bleaching shows that the F-band decreases and shifts towards longer wavelengths. The decrease is accompanied by broadening towards the longer wavelength. The T₂ peak is attributed to Z₁ centres. It is shown that T₁ corresponds to shallow centers and T₃ peak is attributed to F-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.     

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.     

High-temperature X-ray irradiation induced thermoluminescence and half-life calculations in NaYF4 polycrystalline samples

Elevated irradiation temperature studies with NaYF₄ samples reveal that the intensity of the two glow peaks observed around 120 and 180°C enhances. The effect of temperature of irradiation (T_irr) on the sensitisation of the both peaks are studied. The half lives of these glow peaks were calculated and concluded that the half lives of these peaks decreases with the increase in irradiation temperatures.     

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.     

Deposition and properties of a-Si:H by cylindrical diode glow discharge

The effect of plasma parameter on the properties of a-Si:H films prepared by glow discharge process in cylindrical diode system has been studied. The glow discharge plasma is examined by measurements of the emission spectra for H, H₂, SiH and Si radicals, the mass spectra for primary decomposed and secondary polymerized ions, and the rf discharge impedance. The plasma reactions are dominated by the rf electric potential V_p and silane gas pressure p. The nucleation of SiH₂ bonding depends critically on the electron and ion bombardments and the plasma polymerization.     

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.     

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.     

Dye centres in magnesium doped corundum monocrystal

Results of absorption spectra studies in Mg doped Al₂O₃ monocrystals are described. It is shown that due to Mg doping dye centres appear together with the associated additional absorption bands with maxima at 585, 475 and 260 nm. Kinetics of the formation (destruction) of these centres) of these centres in the process of thermal treatment is considered. An assumption on the nature of dye centres and the related absorption bands is proposed together with an evaluation of oscillator strength. Dependences of diffusion coefficients of the subject centres on thermal treatment temperatures are derived.     

Photo-EPR of deformation-produced defects in GaAs

Deformation-produced paramagnetic centres have been studied in GaAs crystals uniaxially compressed at 400° using EPR technique (X band). The effect of light with photon energies from 0.4 to 1.5 eV on the populations of the centres has been investigated. On the basis of the experimental results a model is proposed which locates the energy levels of two of the centres at E_c − 1.05 eV and E_v + 0.75 eV.     

Characteristics of traps in Tl2Ga2Se3S single crystals by low‐temperature thermoluminescence measurements

Defect characterization of Tl₂Ga₂Se₃S single crystals has been performed by thermoluminescence (TL) measurements at low temperatures between 10 and 70 K with various heating rate ranging from 0.6 to 1.0 K/s. The TL signal due to the luminescence from trap centers revealed one glow peak having maximum temperature of 36 K. Curve fitting and various heating rate methods were used for the analysis of the glow curve. The activation energy of 13 meV was found by the application of curve fitting method. This practical method also established that the trap center exhibits the characteristics of mixed (general) kinetic order. In addition, various heating rate analysis gave a compatible result (13 meV) with curve fitting as the temperature lag effect was taken into consideration. Distribution of traps was also investigated using an experimental method. A quasi‐continuous distribution was attributed to the determined trap centers.     

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 and optical absorption studies of NaCl: Gd2+ crystals

Thermal annealing of X-irradiated point defects in gadolinium doped NaCl crystal is investigated by Thermoluminescence (TL) and optical absorption methods. The results of the influence of pre-heat treatment and optical bleaching on glow curves and the production of Z₁-centres are discussed.     

Thermally Stimulated Luminescence of Montmorillonite Clay

X-ray excited luminescence (XL) spectra of montmorillonite clay at RT showed a broad emission band around 380 nm with two shoulders at 340, 450 nm eitherside two sharp peaks and two shoulders are seen at 465, 487, and 548, 576 nm, respectively. The 548 and 576 nm peaks enhanced their intensity at LNT. Whereas thermally stimulated luminescence (TSL) revealed an intense glow peak at 355 K and a weak shoulder around 400 K. Room temperature annealing studies indicated that the 355 K glow peak is not as stable as 400 K shoulder which turns out to be a peak on RT annealing. The X-ray excited luminescence has been attributed to radiative recombination of electrons with holes which are associated with SiO^3-₄, AlO^4-₄ radicals and divalent impurities available in the naturally available clay. TSL is also understood on similar lines. Glow peak reactions are proposed tentatively and their trap parameters have been calculated.     

Neutral radical detection in silane glow-discharge plasma using coherent anti-stokes raman spectroscopy

RF glow discharges of silane have been investigated using CARS technique, and a weak signal assigned to the ν₁ Q-band of SiH₂ has been observed at around 2030 cm^?1 for the first time. The number density of SiH₂ in the plasma has been estimated and is discussed in relation to the magnitude of SiH₄ dissociation rate independently determined also by CARS.     

Kinetics and Trapping Parameters of Thermoluminecence of Sr1−xEuxF2+x Mixed Crystrals

The kinetics and trapping parameters of thermoluminescence of Sr_1−xEu_xF_2+x mixed crystals have been calculated by using different methods. The trap depths, frequency factors, and order of kinetics of glow curve pattern in several compositions of the system revealed variations with composition.     

EPR of Mo5+ in amorphous MoO3 thin films

Mo⁵⁺ centres in amorphous thin films of MoO₃ have been studied as a function of optical density using EPR techniques. Measurements were made for over an order of magnitude change in optical density and down to helium temperatures. A direct correlation between the optical density and the number of Mo⁵⁺ centres is found for low optical densities but further colouration does not continue to increase the number of Mo⁵⁺ centres. A model is proposed to explain the results.     

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.     

Oxidation kinetics of BaF2 single crystals

Oxidation of BaF₂ single-crystals as a result of annealing in air in the temperature range 600° to 900 °C leads to mechanical strengthening. The process kinetics was investigated. It is shown that oxidation takes place in the bulk of crystals owing to oxygen diffusion by formation and growth of oxidation centres. These centres are precipitates of a BaO phase which were revealed by chemical etching.     

UV‐visible emission of (O2‐ ‐ F+) centres in KBr

Single crystals of KBr containing the (O^2‐ ‐ F⁺) color centres and elaborated in atmospheric air by the Czochralski method are studied. The measure of the UV‐visible emission spectra at 78 K present several emission bands situated between 340 and 800 nm. The photoluminescence excitation shows that these emissions are attributed to O^‐₂ and (O^2‐ ‐ F⁺) centres. This study show the new emission bands of (O^2‐ ‐ F⁺) centres which are situated in the UV‐visible spectral domain. The comparison between the emission spectra before and after the thermal treatment of samples shows clearly the transformation of O^‐₂ centers at high temperature to (O^2‐ ‐ F⁺) centres. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)