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.     

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.     

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.     

Formation of Z1 centers in KCI crystals doped with alkaline earth ions under X-irradiation

On the basis of systematic investigations of the shape of the absorption resulting from a superposition of F- and Z₁ bands it is shown that during X-irradiation at RT in KCI crystals doped with alkaline earth ions F centers and Z₁ centers are formed. After an incubation time the ratio of the corresponding concentrations is constant. This is related to a dynamic equilibrium between the F → Z₁ conversion and the destruction of Z₁ centers. A formation mechanism for Z₁ centers is proposed analogously to the well known mechanism for the M center formation under the influence of ionizing radiation.     

Thermoluminescence and optical absorption studies of KBr crystals doped with ca2+

Thermoluminescence studies of KBr crystals doped with 0.5 mole % of Ca²⁺ both in the ‘as-grown’ state and after quenching them from various elevated temperatures indicate that the position of the glow peak which has been assigned to F-centers is found to depend upon the state of dispersion of impurity. Bleaching of the X-irradiated samples result in an additional peak and this has been attributed to Z₁-centers. Optical absorption measurements also confirm the formation of Z₁-centers in Ca²⁺ doped KBr crystals.     

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.     

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.     

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.     

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.     

Transport Properties of (NH4)2 CuCl4.2H2O Low Dimensional Single Crystals

The X‐ray diffraction and Infrared (IR) spectral studies of (NH₄)₂ CuCl₄.2H₂O single crystals reveals that these crystals contains tetragonal crystal structure with the unit cell dimensions of a = 7.58Å, c = 7.95Å, z= 2, β =90° and two water molecules in the unit cell. The temperature dependence of thermally stimulated depolarization current (TSDC) and dc electrical conductivity (σ) studies of this two‐dimensional (NH₄)₂ CuCl₄.2H₂O single crystal have been carried out in 77K–300K temperature region. The TSDC thermograph shows only one sharp peak at 248K with a peak current of 130nA, which is attributed to the Maxwell‐Wagner peak. The activation energy (U), relaxation time (τ) are calculated as 0.78eV and 3.44×10^‐15 s respectively. Dc electrical conductivity studies of these crystals show a first order phase transition at about 248K.     

State of dispersion of impurity on formation of Z1-centres in NaCl:Sr2+ crystals

Thermoluminescence (TL) and Optical absorption studies are carried out to study the bleaching kinetics of F-centre and formation of Z₁-centres in X-irradiated strontium doped NaCl crystals, both in as-grown state and in quenched state. An additional TL peak is observed in this crystal system after F-bleaching of irradiated samples which is attributed to thermal annealing of Z₁-centres. Various models proposed for Z₁-centres are reviewed in the light of these results and it is concluded that Z₁-centres are associated with impurity-vacancy dipoles.     

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.     

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.     

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.     

Spectroscopic studies of lead arsenate glasses doped with nickel oxide

Lead arsenate glasses containing different concentrations of NiO ranging from 0 to 1 mol% (in steps of 0.2 mol%) were prepared. The samples were characterized by X-ray diffraction and differential thermal analysis. A number of studies viz., optical absorption, thermoluminescence, magnetic susceptibilities and IR spectra, have been carried out on these glasses. The bands observed in the optical absorption spectra of the glasses have been analyzed using Tanabe-Sugano diagrams for d⁸ ion; the analysis indicates the presence of Ni²⁺ ions in both tetrahedral and octahedral positions. The increase in the concentration of NiO in the glass matrix shows a gradual transformation of nickel ions from tetrahedral positions to octahedral positions in the glass network. The thermoluminescence light output of the X-ray irradiated glasses has exhibited a glow peak at 353 K (with increasing intensity with an increase in the concentration of NiO) in addition to the conventional peak due to the recombination of electron-hole centers; this glow peak is identified due to ³T₂ → ³A₂ emission transition of octahedral Ni²⁺ ions. The value of the magnetic moment evaluated from the measured magnetic susceptibility show a decreasing trend from 3.84 to 3.10 μ_B with the increase in the concentration of NiO. All these studies indicate an increasing presence of octahedral (lasing) Ni²⁺ ions in these glasses with the increase in the concentration of NiO.     

Electrical conductivity of CsCuCl<Subscript>3</Subscript> crystals at structural phase transition

The electrical conductivity σ of CsCuCl₃ single crystals synthesized by the crystallization method from aqueous solutions in the ternary CsCl–CuCl₂–H₂O system has been studied. The σ measurements for CsCuCl₃ crystals have been carried out in the temperature range of 397–455 K, which covers the structural phase transition from the low-temperature (sp. gr. P6₁22, Z = 6) to the high-temperature (sp. gr. P6₃mc, Z = 2) modification at T _tr = 423 ± 8 K. A jump of σ by a factor of ~3 is observed on the σ(T) dependence in the region of the structural transition, which indicates the existence of first-order phase transition. The electric transfer activation enthalpies ΔHσ are found to be 1.0 ± 0.1 eV at T > T _tr and 0.8 ± 0.1 eV at T < T _tr. The σ value for CsCuC_l3 crystals amounts to 7 × 10^–6 S/cm at 455 K.     

Temperature dependence of the dielectric parameters of nonstoichiometric SrTiO3 single crystals

The results of experimental studies of the temperature dependence of the low-frequency permittivity ε ₀ and the loss tangent taδ of nominally undoped and doped single crystals of strontium titanate at T = 10–300 K are given. The samples were doped with ions of iron-group metals (V, Mn, Fe, Co) and/or ions of rare earth metals (Pr, Nd, Sm, Tm) with concentrations of 10^?3?5 × 10^?1 at %. Anomalous temperature dependences ε₀ T and tanδ(T) were found for a number of samples. The anomalies found were attributed to the violation of stoichiometry of the single crystals under study and the transition of some fraction of Ti⁴⁺ ions to the Ti³⁺ state.     

Effect of change of state of aggregation of impurity on tl and microhardness of KClxBr1–x mixed crystals doped with Ca2+

Microhardness and Thermoluminescence (TL) measurements have been made in KCl_xBr_1–x mixed crystals doped with Ca²⁺ impurity. The variation of hardness in undoped and Ca²⁺ doped KCl_xBr_1–x crystals with quenching temperature is investigated. TL studied of KCl_xBr_1–x crystals doped with Ca²⁺, both in as-grown state and after quenching them from various elevated temperatures indicate that the positions of the glow peak which has been attributed to F-centers is found to depend upon the state of dispersion of impurity.     

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.     

Phase transitions in Cs5(HSO4)2(H2PO4)3 crystal

The symmetry (sp. gr.I $\bar 4$ 3d) and lattice parameters have been determined for the first time for Cs₅(H₂SO₄)₂(H₂PO₄)₃ crystals in the temperature range from 172 to 390 K. The thermal and optical properties of crystals, as well as their conductivity, have been investigated at elevated temperatures. It is shown that a crystal heated to T = 365 K undergoes a phase transition with symmetry lowering to the tetragonal phase (with the parameters a = 4.965(1) Å and c = 5.016(1) Å), while at T ≈ 390 K a phase transition to the cubic phase is presumably observed. With a decrease in temperature, a phase transition without a change in symmetry occurs at T = 240 K.