Role of Impurity Precipitates on Microhardness of KBr:Ba2+ Crystals

Microhardness of KBr crystals doped with various concentration of Ba²⁺ have been investigated in the asgrown state and after quenching from various elevated temperatures. It is observed that hardness increases with increase in impurity concentration and at high concentration the hardness starts decreasing. Microstructural investigations have showed the formation of visible precipitates at high concentrations. The heat treatment studies showed that in crystals quenched from elevated temperatures the visible precipitates dissociate and hardness increases.     

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.     

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.     

Cosmic Strings and Domain Walls in a Scale-Covariant Theory of Gravitation

Axially symmetric space-time is considered in the presence of cosmic string source and thick domain walls in the frame work of a scale-covariant theory of gravitation. A relation between metric potential is assumed to get a determinate solution of the field equations of this theory. In this particular case, it is observed that the geometric (Nambu) string p-string (Takabayasi string) and Reddy string do not survive. It is also seen that the stiff (self-gravitating) domain walls do not exist in this theory.     

Spectroscopic and photoluminescence characteristics of Dy ions in lead containing sodium fluoroborate glasses for laser materials

Lead containing calcium zinc sodium fluoroborate (LCZSFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. The experimentally determined oscillator strengths have been determined by measuring the areas under the absorption peaks and the Judd–Ofelt (J–O) intensity parameters were calculated using the least squares fit method. From the evaluated J–O parameters the radiative transition probability rates, radiative lifetimes and branching ratios were calculated for ⁴F_9/2 excited level. Room temperature photoluminescence spectra for different concentrations of Dy³⁺-doped LCZSFB glasses were obtained by exciting the glass samples at 386 nm. The intensity of Dy³⁺ emission spectra increases with increasing concentration of 0.1, 0.25, 0.5 and 1.0 mol% and beyond 1.0 mol% the concentration quenching is observed. The measuring branching ratios are reasonably high for transitions ⁴F_9/2→⁶H_15/2 and ⁶H_13/2, suggesting that the emission at 484 and 576 nm, respectively, can give rise to lasing action in the visible region. From the visible emission spectra, yellow–blue (Y/B) intensity ratios and chromaticity color coordinates were also estimated. The lifetimes of ⁴F_9/2 metastable state for the samples with different concentrations were also measured and discussed.     

Optical absorption spectrum of Co2+ in ammonium perchlorate single crystal

Single crystals of cobalt — doped ammonium perchlorate were grown at room temperature. The electronic absorption bands observed at room and liquid air temperatures have been assigned transitions from the ground⁴T₁(F) state to the excited⁴T₂(F),⁴A₂(F),²T₁(G) and⁴T₁(P) states. The crystal parameters derived areDq=880 cm^–1,B=865 cm^–1 andC= 4·63B.The authors wish to express their thanks to the authorities of the Indian Institute of Science, Bangalore for kind permission to use their spectrophotometer. Two of the authors (B. C. V.Reddy and J. L.Rao) express their greatful thanks to the council of scientific and Industrial Research (New Delhi) for financial assistance.     

Poisson structures due to Lie algebra representations

Using a unitary solution of the classical Yang-Baxter equation on a Lie algebraG we describe a particular way of constructing homogeneous quadratic Poisson structures on the dual of aG-moduleV and study some local features of the symplectic foliation due to the involutive distribution of the Hamiltonian vector fields. We also give some examples where the symplectic leaves are explicitly calculated.