EPR, thermo and photoluminescence properties of ZnO nanopowders

Nanocrystalline ZnO powders have been synthesized by a low temperature solution combustion method. The photoluminescence (PL) spectrum of as-formed and heat treated ZnO shows strong violet (402, 421, 437, 485 nm) and weak green (520 nm) emission peaks respectively. The PL intensities of defect related emission bands decrease with calcinations temperature indicating the decrease of Zn(i) and V(o)(+) caused by the chemisorptions of oxygen. The results are correlated with the electron paramagnetic resonance (EPR) studies. Thermoluminescence (TL) glow curves of gamma irradiated ZnO nanoparticles exhibit a single broad glow peak at similar to 343 degrees C. This can be attributed to the recombination of charge carriers released from the surface states associated with oxygen defects, mainly interstitial oxygen ion centers. The trapping parameters of ZnO irradiated with various gamma-doses are calculated using peak shape method. It is observed that the glow peak intensity increases with increase of gamma dose without changing glow curve shape. These two characteristic properties such as TL intensity increases with gamma dose and simple glow curve structure is an indication that the synthesized ZnO nanoparticles might be used as good TL dosimeter for high temperature application. (C) 2011 Elsevier B.V. All rights reserved.

Structural and phase dependent thermo and photoluminescent properties of Dy(OH)(3) and Dy2O3 nanorods

Hexagonal Dy(OH)(3) and cubic Dy2O3 nanorods were prepared by hydrothermal method. Dy(OH)(3) nanorods was directly obtained at 180 degrees C for 20 h after hydrothermal treatment whereas subsequently heat treatment at 750 degrees C for 2 h gives pure cubic Dy2O3. SEM micrographs reveal that needle shaped rods with different sizes were observed in both the phases. TEM results also confirm this. The TL response of hexagonal Dy(OH)(3) and cubic Dy2O3 nanorods have been analyzed for gamma-irradiation over a wide range of exposures (1-5 kGy). TL glow peak intensity increases with gamma dose in both the phases. The activation energy (E), order of kinetics (6), and frequency factor (s) for both the phases have been determined using Chen's peak shape method. The simple glow curve shape, structure and linear response to gamma-irradiation over a large span of exposures makes the cubic Dy2O3 as a useful dosimetric material to estimate high exposures of gamma-rays. (c) 2012 Elsevier Ltd. All rights reserved.

Synthesis, characterization, EPR, photo and thermoluminescence properties of YAlO3:Ni2+ nanophosphors

YAlO3:Ni2+ (0.1 mol%) doped nanophosphor was synthesised by a low temperature solution combustion method. Powder X-ray diffraction (PXRD) confirms the orthorhombic phase of yttrium aluminate (YAlO3) along with traces of Y3Al5O12. Scanning Electron microscopy (SEM) shows that the powder particles appears to be spherical in shape with large agglomeration. The average crystallite sizes appeared to be in the range 45-90 nm and the same was confirmed by transmission electron microscopy (TEM) and Williamson-Hall (W-H) plots. Electron Paramagnetic Resonance (EPR) and photoluminescence (PL) studies reveal that Ni2+ ions are in octahedral coordination. Thermoluminescence (TL) glow curve consists of two peaks with the main peak at similar to 224 degrees C and a shouldered peak at 285 degrees C was recorded in the range 0.2-15 kGy gamma-irradiated samples. The TL intensity was found to be increasing linearly for 224 degrees C and 285 degrees C peaks up to 1 kGy and thereafter it shows sub-linear (up to 8 kGy) and saturation behavior. The trap parameters namely activation energy (E), order of kinetics (b), frequency factor (s) at different gamma-doses were determined using Chens glow peak shape and Luschiks methods then the results are discussed in detail. Simple glow peak structure, the 224 degrees C peak in YAlO3:Ni2+ nanophosphor can be used in personal dosimetry. (C) 2012 Elsevier B.V. All rights reserved.

Structural, iono and thermoluminescence properties of heavy ion (100 MeV Si7+) bombarded Zn2SiO4:Sm3+ nanophosphor

Structural, iono (IL) and thermoluminescence (TL) studies of Zn2SiO4:Sm3+ (1-5 mol%) nanophosphor bombarded with swift heavy ions in the fluence range 3.91 x 10(12)-21.48 x 10(12) cm(-2) have been carried out. The average crystallite sizes for pristine and ion irradiated for 3.91 x 10(12) ions cm(-2) and 21.48 x 10(12) ions cm(-2) were found to be 34, 26 and 20 nm. With increase of ion fluence, the intensity of XRD peaks decreases and FWHM increases. The peak broadening indicates the stress induced point/clusters defects produced due to heavy ion irradiation. IL studies were carried out for different Sm3+ concentrations in Zn2SiO4 by irradiating with ion fluence of 15.62 x 10(12) ions cm(-2). The characteristic emission peaks at similar to 562, 599, 646 and 701 nm were recorded by exciting Si7+ ions in the fluence range 3.91 x 10(12)-21.48 x 10(12) ions cm(-2). These peaks were attributed to (4)G(5/2)-> H-6(5/2) (562 nm), (4)G(5/2)-> H-6(7/2) (599 nm), (4)G(5/2)-> H-6(9/2) (646 nm), and (4)G(5/2)-> H-6(5/2) (701 nm) transitions of Sm3+. The highest emission was recorded at 3 mol% of Sm3+ doped Zn2SiO4. TL studies were carried out for 3 mol% Sm3+ concentration in the fluence range 3.91 x 10(12)-21.48 x 10(12) ions cm(-2). Two U glow peaks at 152 and 223 degrees C were recorded. The kinetic parameters (E, b, and s), were estimated using Chen's peak shape method. Simple glow curve structure (223 degrees C), highly resistive, increase in TL. intensity up to 19.53 x 10(12) ions cm(-2), simple trap distribution makes Zn2SiO4:Sm3+ (3 mol%) phosphor highly useful in radiation dosimetry.

Auto-ignition based synthesis of Y2O3 for photo- and thermo-luminescent applications

We present a simple route for synthesis of Y2O3 for both photoluminescent (PL) and thermoluminescent (TL) applications. We show that by simply switching the fuel from ethylene di-amine tetracetic acid (EDTA) to its disodium derivative (Na-2-EDTA), we obtain a better photoluminescent material. On the other hand, use of EDTA aids in formation of Y2O3 which is a better thermoluminescent material. In both cases pure cubic nano-Y2O3 is obtained. For both the material systems, structural characterization, photoluminescence, thermoluminescence, and absorbance spectra are reported and analyzed. Use of EDTA results in nano Y2O3 with crystallite size similar to 10 nm. Crystallinity improves, and crystallite size is larger (similar to 30 nm) when Na-2-EDTA is used. TL response of Y2O3 nanophosphors prepared by both fuels is examined using UV radiation. Samples prepared with EDTA show well resolved glow curve at 140 degrees C, while samples prepared with Na-2-EDTA shows a glow curve at 155 degrees C. Effect of UV exposure time on TL characteristics is investigated. The TL kinetic parameters are also calculated using glow curve shape method. Results indicate that the TL behavior of both the samples follow a second order kinetic model. (C) 2013 Elsevier B.V. All rights reserved.

Gd1.96-xYxEu0.04O3 (x=0.0, 0.49, 0.98, 1.47, 1.96 mol%) nanophosphors: Propellant combustion synthesis, structural and luminescence studies

Gd1.96-xYxEu0.04O3 (x = 0.0, 0.49, 0.98, 1.47, 1.96 mol%) nanophosphors were synthesized by propellant combustion method at low temperature (400 degrees C). The powder X-ray diffraction patterns of as formed Gd1.96Eu0.04O3 showed monoclinic phase, however with the addition of yttria it transforms from monoclinic to pure cubic phase. The porous nature increases with increase of yttria content. The particle size was estimated from Scherrer's and W-H plots which was found to be in the range 30-40 nm. These results were in well agreement with transmission electron microscopy studies. The optical band gap energies estimated were found to be in the range 5.32-5.49 eV. PL emission was recorded under 305 nm excitation show an intense emission peak at 611 nm along with other emission peaks at 582, 641 nm. These emission peaks were attributed to the transition of D-5(0) —> F-7(J) (J = 0, 1, 2, 3) of Eu3+ ions. It was observed that PL intensity increases with increase of Y content up to x = 0.98 and thereafter intensity decreases. CIE color co-ordinates indicates that at x = 1.47 an intense red bright color can be achieved, which could find a promising application in flat panel displays. The cubic and monoclinic phases show different thermoluminescence glow peak values measured under identical conditions. The response of the cubic phase to the applied dose showed good linearity, negligible fading, and simple glow curve structure than monoclinic phase indicating that suitability of this phosphor in dosimetric applications. (C) 2014 Elsevier B.V. All rights reserved.

Effect of curve crossing on absorption and resonance Raman spectra: analytical treatment for delta-function coupling in parabolic potentials

We propose an exactly solvable model for the two-state curve-crossing problem. Our model assumes the coupling to be a delta function. It is used to calculate the effect of curve crossing on the electronic absorption spectrum and the resonance Raman excitation profile.

Co-2-Ions In A Low-Pressure Glow-Discharge Of Carbon-Dioxide

$CO_2^{-}$ ions have been detected in the gas phase and measured by a mass spectrometer with a flight time of 30 µs in the positive column of carbondioxide glow discharge.

05-ions in a low pressure glow discharge of oxygen

0:- ions have been detected and measured in a positive column of glow discharge in oxygen between 0.04 and 0.17 Torr. A suitable ion-molecule reaction has been proposed, which appears to be supported by the mass spectrometer measurements.

Coexistence curve of acetonitrile and cyclohexane liquid system

The paper reports a detailed determination of the coexistence curve for the binary liquid system acetonitrile+cyclohexane, which have very closely matched densities and the data points get affected by gravity only for t=(Tc−T)/ Tc[approximately-equal-to]10−6. About 100 samples were measured over the range 10−6curve appear symmetric in the new variables is pointed out. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.

On the Purity of Atmospheric Glow-Discharge Plasma

Purity of the glow-discharge plasma at atmospheric pressure for surface modification applications is always debatable, since it works at ambient atmosphere. We have demonstrated on the use of optical emission spectroscopy to test the purity of this kind of plasma. The effect of gas flow pattern, nature of gas, and its flow rate on the plasma chemistry was studied. The importance of proper system design in maintaining a uniform flow of heavy and inert gases as carrier gas in atmospheric glow-discharge plasma was confirmed. The surface of a plasma-treated PET sample was analyzed using X-ray photoelectron spectroscopy to verify the studies on plasma purity done using emission spectrum.

Liquid-liquid critical phenomena. The coexistence curve of n-heptane-acetic anhydride

The coexistence curve of the binary liquid mixture n-heptane-acetic anhydride has been determined by the observation of the transition temperatures of 76 samples over the range of compositions. The functional form of the difference in order parameter, in terms of either the mole fraction or the volume fraction, is consistent with theoretical predictions invoking the concept of universality at critical points. The average value of the order parameter, the diameter of the coexistence curve, shows an anomaly which can be described by either an exponent 1 - a, as predicted by various theories (where a is the critical exponent of the specific heat), or by an exponent 20 (where P is the coexistence curve exponent), as expected when the order parameter used is not the one the diameter of which diverges asymptotically as 1 - a.

Acoustic emission source location in composite structure by Voronoi construction using geodesic curve evolution

Conventional analytical/numerical methods employing triangulation technique are suitable for locating acoustic emission (AE) source in a planar structure without structural discontinuities. But these methods cannot be extended to structures with complicated geometry, and, also, the problem gets compounded if the material of the structure is anisotropic warranting complex analytical velocity models. A geodesic approach using Voronoi construction is proposed in this work to locate the AE source in a composite structure. The approach is based on the fact that the wave takes minimum energy path to travel from the source to any other point in the connected domain. The geodesics are computed on the meshed surface of the structure using graph theory based on Dijkstra's algorithm. By propagating the waves in reverse virtually from these sensors along the geodesic path and by locating the first intersection point of these waves, one can get the AE source location. In this work, the geodesic approach is shown more suitable for a practicable source location solution in a composite structure with arbitrary surface containing finite discontinuities. Experiments have been conducted on composite plate specimens of simple and complex geometry to validate this method.

Multi-channel curve crossing problems: analytically solvable model

We have proposed a general method for finding the exact analytical solution for the multi-channel curve crossing problem in the presence of delta function couplings. We have analysed the case where aa potential energy curve couples to a continuum (in energy) of the potential energy curves.

Real Theta Characteristics And Automorphisms Of A Real Curve

Let X be a geometrically irreductble smooth projective cruve defined over R. of genus at least 2. that admits a nontrivial automorphism, sigma. Assume that X does not have any real points. Let tau be the antiholomorphic involution of the complexification lambda(C) of X. We show that if the action of sigma on the set S(X) of all real theta characteristics of X is trivial. then the order of sigma is even, say 2k and the automorphism tau o (sigma) over cap (lambda) of X-C has a fixed point, where (sigma) over cap is the automorphism of X x C-R defined by sigma We then show that there exists X with a real point and admitting a nontrivial automorphism sigma, such that the action of sigma on S(X) is trivial, while X/ not equal P-R(1) We also give an example of X with no real points and admitting a nontrivial automorphisim sigma such that the automorphism tau o (sigma) over cap (lambda) has a fixed point, the action of sigma on S(X) is trivial, and X/ not equal P-R(1)