bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiation effects in sapphire optical fibers
Authors: Sporea Dan , Sporea Adelina 
Published: March 2007

AbstractRadiation effects on sapphire optical fibers were investigated using off‐line gamma‐ray, neutron and electron beam irradiation and on‐line proton irradiation. The optical attenuation of these optical fibers was studied from UV to IR (200 nm – 1700 nm). For the in‐situ measurements radioluminescence was also investigated as function of the total irradiation dose. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Holographic properties of azobenzene oligomers with differently bonded chromophore groups
Authors: Ozols A. , Saharov Dm. , Kampars V. , Kokars V. , Kreicberga J. , Ratyeva S. 
Published: March 2007

AbstractHolographic properties of two types (I and II, specified in the text) of azobenzene oligomers (ABO) have been experimentally studied in the spectral region of low absorption at 633 nm. In the case of type I ABO the chromophore groups were covalently bonded to either tolyl‐polyurethane or hexamethylene‐polyurethane matrix. In the case of type II ABO azobenzene chromophores were dispersed in polystyrene matrix, and their concentration was varied from 0.005 to 0.200 mol/l. Samples were in the form of 10 µm thick films. In both cases the diffraction efficiency exposure time dependences were measured for the holographic grating period of 2 (m at 633 nm. The diffraction efficiency of more than 2% and the specific recording energy down to 30 ‐ 60 J/(cm2%) were achieved in both cases. In the case of type I ABO the best results were achieved with 4‐nitronaphtylazobenzene chromophore groups in hexamethylene‐polyurethane matrix. The chromophore concentration threshold within 0.01 – 0.04 mol/l range, the holographic efficiency growth with chromophore concentration and the photosensitization effect were found in the case of type II ABO. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fractal characteristics of metal clusters self‐assembled in alkali halide matrices
Authors: Enculescu M. , Enculescu I. 
Published: March 2007

AbstractMetal nanoclusters of Ag and Au were obtained in alkali halide crystals (NaCl, KBr and KCl). The fractal character of the structures is proved by the fractal dimensions calculated using a home made computer program. The self aggregation of the metallic structures is governed in both cases (Ag and Au) by the DLA mechanism. This is proved by the values of the fractal dimension calculated using two methods, sandbox and box‐counting, which are between 1.7 and 1.8 for Ag and for Au between 1.7 and 1.9. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman studies of ferroelectric domain walls in lithium tantalate and niobate
Authors: Capek Pavel , Stone Greg , Dierolf Volkmar , Althouse Chad , Gopolan Venkat 
Published: March 2007

AbstractUsing confocal Raman spectroscopy at low temperature we investigated the perturbation of the phonon modes across a domain wall region as a function of sample stoichiometry in lithium tantalate and niobate. For all samples, we found that the Raman spectra were changed. The intensity of the A(LO) phonon modes and most of the E(TO) phonon modes were shifted and changed in their relative intensity over a 20 μm length scale. Our measurements suggest that the intensity of the A(LO) phonon modes change due to local charges induced by pyroelectric effect and/or photoionization, while the observed shifts are due to strains that are not relaxed in the domain wall region. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relative features of the principal and secondary luminescence lifetimes in quartz
Authors: Chithambo M.L. , Ogundare F.O. 
Published: March 2007

AbstractThe form of time‐resolved luminescence spectra has been studied for quartz annealed at 800 °C and pulse‐stimulated at 470 nm. Depending on the measurement temperature and the irradiation dose, the spectra may be de‐convolved into two possible components to produce a principal and subsidiary lifetime component. Measurements between 20 and 200 °C show that both components are affected by thermal quenching of the associated luminescence, qualitatively so for the subsidiary one, but with an activation energy of 0.71 eV for the principal lifetime. Regarding influence of irradiation, time‐resolved spectra consist of a single component below about 260 Gy but two components thereafter independent of irradiation. The irradiation‐dependent features of the lifetimes are accounted for in terms of the relative importance of the various luminescence centers in quartz. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anomalous zero‐phonon line broadening of the (NV)– center in diamond
Authors: Nishikori H. , Mita Y. , Nisida Y. , Okada M. , Nakashima T. 
Published: March 2007

AbstractAbsorption measurements were carried out on the (NV)– centers in diamond at low temperature after laser illumination. It was observed that the width of the zero‐phonon line becomes persistently more than two times larger. This characteristic phenomenon was studied in detail about excitation photon energy, illumination time, sample temperature and recovery nature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron paramagnetic resonance line shape investigation of the 29Si hyperfine doublet of the E′γ center in a‐SiO2
Authors: Buscarino Gianpiero , Agnello Simonpietro , Parlato Aldo 
Published: March 2007

AbstractWe report an experimental study by electron paramagnetic resonance (EPR) spectroscopy of the E′γ center and of its hyperfine structure, consisting in a pair of lines split by 42 mT. Our results show that two types of E′γ centers can be distinguished on the basis of the EPR line shapes of their main resonance line and hyperfine structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dielectric spectra of doped and X‐ray irradiated calcium fluoride crystals
Authors: Nicoara I. , Munteanu M. , Pecingina‐Garjoaba N. , Stef M. , Preda E. , Lucaci A. 
Published: March 2007

AbstractCalcium fluoride crystals doped with PbF2 and codoped with LiF, NaF have been grown using the vertical Bridgman method. The frequency (1‐100 kHz) dependence of the real and imaginary parts of the complex dielectric constant, ε1 and ε2, have been studied in the temperature range 160‐300 K; the activation parameters of the relaxation process have been determined for various doped and X‐irradiated calcium fluoride crystals. The optical absorption spectra of the crystals are also investigated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extended defects in organic molecular semiconductors: the role of crystal growth mechanisms
Authors: Moret M. , Campione M. , Raimondo L. , Sassella A. , Tavazzi S. , Aquilano D. 
Published: March 2007

AbstractAtomic force and optical microscopy analysis of topographic features on the {001} faces of the organic semiconductor quaterthiophene is employed to establish connections between bulk and surface structure. Observation of interlaced step patterns on growth spirals is indicative of the presence of layers rotated by 180° about the normal of the (001) crystal face. This result, together with the height of the exposed step ledges of the order of 10‐100 nm, suggests the complex polytypic nature of these crystals due to periodic polysynthetic twinning. Therefore, the basic monoclinic structure of quaterthiophene is modified giving rise to many different periodicities along [001] even in one crystallite. The consequences on physical properties of these phenomena arising from growth mechanisms are briefly discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman and infrared spectroscopic characterization of LiNbO3 crystals grown from alkali metal oxide solvents
Authors: Dravecz G. , Kovács L. , Péter Á. , Polgár K. , Bourson P. 
Published: March 2007

AbstractLiNbO3 crystals grown from Na2O, Rb2O, and Cs2O containing fluxes were characterized by infrared and Raman spectroscopic methods. Pure, nearly stoichiometric crystals with 49.7–50.0 mol% Li2O content were obtained from solvents containing Rb2O and Cs2O, while Na2O entered the crystal as a dopant. The intensity ratio of two OH– absorption peaks at 3480 and 3465 cm–1 in thermal equilibrium was shown to be a useful and accurate parameter for the determination of the lithium content of pure LiNbO3 crystals close to the stoichiometric composition. From the remarkable change of both infrared and Raman spectra in crystals grown from Na2O solvent, the incorporation of Na on Li sites was assumed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tin nanoclusters obtained in potassium chloride by thermal annealing
Authors: Apostol E. , Enculescu M. , Polosan S. , Vasile E. , Topa V. 
Published: March 2007

AbstractTin nanoclusters were obtained in potassium chloride crystals following the electrolytic coloration of KCl:Sn2+ and KCl: Sn2++Ca2+ crystals and thermal annealing at various temperatures and times. Electrolytic coloration of KCl:Sn2+ crystals produces electronic centers inside of samples, presumably negative metal ions of tin. Optical absorption measurements were performed on as grown sample, colored and thermal annealed samples. The behavior of the samples with Sn colloids was compared with theoretical predictions according to Mie's theory. Tin nanoclusters in KCl exhibit an absorption band with a peak at 215 nm. The structure of the nanoclusters was studied by optical absorption and transmission electron microscopy means. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectroscopic methods for the determination of the composition of potassium lithium niobate crystals
Authors: Hajdara I. , Lengyel K. , Dravecz G. , Kovács L. , Péter Á. , Szaller Zs. 
Published: March 2007

AbstractBeside the ferroelectric Curie‐temperature, the ultraviolet and infrared spectra of potassium lithium niobate (K3Li2Nb5O15, KLN) were shown to be very sensitive to the compositional variations observed in the crystals along the growth axis. The absorption edge shifts to the UV with decreasing Nb content, independently of the K/Li ratio of the crystal, while the ratio of the intensities of the OH– stretching vibrational bands at 3440 and 3520 cm–1 depends on the K/Li ratio, as well. Combining these optical spectroscopic methods with Curie‐temperature measurements one can determine the crystal composition with high accuracy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermoluminescence of LiF and F2 color centers
Authors: Baldacchini G. , Davidson A. T. , Kalinov V. S. , Kozakiewicz A. G. , Montereali R. M. , Nichelatti E. , Voitovich A. P. 
Published: March 2007

AbstractLight emitted when heating crystalline materials previously exposed to ionizing radiation is commonly known as thermoluminescence. The resultant glow curve is related to the material, the impurities and the defect centers generated by the irradiation. Several efforts have been made in the past to associate glow peaks with specific defect centers. Recently, in the case of LiF we established a link between F3+ and F3 centers and the temperature region of the glow curve below 200 °C. This result was obtained by using especially treated samples with known concentration of color centers in first place, and annealing measurements in second place. By continuing these studies, it has been possible to establish a further link between F2 centers and a prominent feature of the glow curve near 260 °C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical absorption, paramagnetic resonance and depolarisation currents in MgAl2O4 spinel
Authors: Paiva Roberto , Carvalhaes Magalhães , Blak Ana Regina 
Published: March 2007

AbstractOptical Absorption (OA), Electron Paramagnetic Resonance (EPR) and Thermally Stimulated Depolarisation Currents (TSDC) techniques were applied to study the effects of irradiation and thermal treatments in the formation, aggregation and destruction processes of dipole defects in MgAl2O4 spinel. Irradiated MgAl2O4 crystals present two OA bands centred at 3.4 eV and 5.1 eV. The 3.4 eV band increases with the irradiation‐dose, stabilizes its maximum height for doses near 10 kGy and is completely destroyed for thermal treatments above 500 K. This same band decays when the sample is maintained at room temperature reaching a constant value after a few weeks. The EPR spectrum is composed by two superimposed bands at g = 2.011. The gamma dose dependence, the thermal treatments between 370 K and 500 K and the thermal decay of the two bands at room temperature, show that each band behaves in a different way thus indicating that they are associated with two different defects. Gamma dose of 10 kGy produces a TSDC band at 245 K. When the sample is maintained at room temperature, after the gamma irradiation, for several weeks, a displacement in the peak position to 290 K, is observed. Thermal treatments above 500 K destroy the 290 K band. This band is associated to at least two V‐type centres. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Decay time of polaron photoluminescence in congruent lithium niobate
Authors: Harhira A. , Guilbert L. , Bourson P. , Rinnert H. 
Published: March 2007

AbstractThe intensity, the peak wavelength and the decay time of polaron photoluminescence in congruent lithium niobate are measured versus temperature from 77 K to 290 K. The radiative relaxation shows quasi athermal behaviour (τR ≈ 9 µs) whereas the nonradiative relaxation follows arrhenius law with activation energy of 220 meV. The crossing point between radiative and nonradiative lifetimes is about 210 K. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formation of the condensed phase on a surface of fiber crystals during their growth by micro pulling down method
Authors: Cherepanova E. V. , Tcherepanov A. N. , Shulgin B. V. 
Published: March 2007

AbstractNew experimental data of the structure of a surface of fiber crystals (NaF, LiF and BGO) are presented in this paper. The explanation of observable features of a structure of their surface is offered. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
UV light energy storage and thermoluminescence in AlN ceramics
Authors: Trinkler L. , Berzina B. , Auzina A. , Benabdesselam M. , Iacconi P. 
Published: March 2007

AbstractAlN ceramics, untreated and subjected to oxygen ion implantation, are studied for potential application in TL dosimetry of UV light. Based on photoluminescence and thermoluminescence measurements there are shown advantages of the selection of the 480 emission band for TL signal recording instead of the previously used 400 nm band: higher intensity of the TL signal, lower fading rate of the accumulated TL signal, excitation region (270‐340 nm) corresponding to UV‐B range, monitoring of which is actual in UV dosimetry. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coloured inorganic‐organic films on glass
Authors: Cholewa‐Kowalska K. , Wojtach K. , Olejniczak Z. , Laczka M. 
Published: March 2007

AbstractTwo kinds of inorganic‐organic hybrid materials (A and B class) were obtained in the form of thin films on glass. As starting materials were used: PhTES + TEOS (A class); PhTES + GPTMS + TBA (B class). Hybrid materials were coloured using ORASOL type dyes. The coloured coatings were put on glass by dip‐coating technique. The structure of hybrid matrix was examined by spectroscopic methods: FTIR, 29Si MAS NMR, 27Al MAS NMR. On this base structural units of hybrid were identified. UV/VIS spectra of thin films were measured directly after obtainment as well as after thermal and chemical treatment of samples. It has been found that UV/VIS spectra originate from electron transitions between ligands and transition metal ions. The coloured centres in hybrid matrix show good thermal and chemical resistance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence of nanoporous C12A7 compound
Authors: Feldbach E. , Kirm M. , Liblik P. , Maaroos A. , Avarmaa T. , Mändar H. 
Published: March 2007

AbstractA comparison of excitation spectra of photostimulated and ordinary luminescence enabled us for the first time to determine experimentally the framework energy gap value Eg= 6.5 eV of 12CaO · 7 Al2O3(C12A7). The most short‐wavelength luminescence band (peaked at ∼4.5 eV) detected at 10 K can be interpreted either as luminescence of intrinsic excitations or as recombination of electrons, captured in sub‐nanometer sized cages of C12A7 crystal structure, with holes of valence band. The main peak of thermostimulated luminescence (134–137 K) is composed of two emission bands peaked at 2.8 and 4.5 eV. The calculated activation energy 0.44 eV of spectrally resolved (at 4.5 eV) thermally stimulated luminescence peak at 137 K is close to the value (0.4 eV) needed to initiate the inter‐cage charge transfer of electrons (polaron hopping) between cages. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal transformation of colour centres in LiF crystals with given content of oxygen, hydroxyl and metal ions
Authors: Baldacchini G. , Goncharova O. , Kalinov V. S. , Montereali R. M. , Vincenti A. , Voitovich A. P. 
Published: March 2007

AbstractProcesses of radiation creation and annealing of Frenkel defects, as well as their transformation processes, have been studied in γ ‐irradiated LiF single crystals containing various impurities, by means of measurements of thermally stimulated changes in absorption and emission spectra. Important information about the density of colour centres in LiF, which depends on γ ‐irradiation doses, impurities and temperatures, has been obtained for small crystal contents of oxygen, hydroxyl and metal ions. A comparison of annealing parameters of the LiF crystals subjected to different doses of irradiation, but to the same thermal bleaching procedures, has been performed and the results are critically discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic transitions in Li2B4O7:Cu single crystals
Authors: Nagirnyi V. , Kotlov A. , Corradi G. , Watterich A. , Kirm M. 
Published: March 2007

AbstractA low‐temperature study of Li2B4O7:Cu crystals by methods of time‐resolved polarization spectroscopy using synchrotron radiation in the 4–20 eV region and microsecond Xe flash lamp pulses in the 3–6 eV region is reported. The results strongly support the conclusion about a low‐symmetry position of the Cu+ ion in its ground state. The temperature dependence of the decay kinetics of the Cu+‐related 3.35 eV emission indicates a triplet nature for the relaxed excited state of the Cu+ centres. A pseudo off‐centre position of the Cu+ ion in the relaxed excited state is suggested. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydroxil ions in scheelite type molybdates and tungstates
Authors: Kovács L. , Péter Á. , Ivleva L. I. , Baraldi A. , Capelletti R. 
Published: March 2007

AbstractThe presence of hydroxil ions has been detected for the first time in as‐grown scheelite type crystals. A number of stretching vibrational bands were observed in PbMoO4 and BaWO4 crystals at 8 K, while only very weak OH– absorption was found in CaMoO4, SrMoO4 and SrWO4 in the 3200–3600 cm–1 wavenumber range. The anharmonicity of the stretching modes for all bands in PbMoO4 and BaWO4 was found to be in agreement with that observed in other oxides. The model of weak coupling to a single phonon band was used to interpret the temperature dependence of the OH– band positions and halfwidths. Strong polarization dependence was observed for the OH– vibrations in both crystals indicating that the O–H dipoles incorporate the lattice along different O–O bonds. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nanocrystalline SrTiO3:Eu3+ and BaTiO3:Eu3+: fluorescence spectroscopy and optical studies of structural phase transitions
Authors: Feofilov S. P. , Kaplyanskii A. A. , Kulinkin A. B. , Zakharchenya R. I. 
Published: March 2007

AbstractThe results of optical studies of Eu3+ ions doped nanocrystalline materials which undergo structural phase transitions: SrTiO3:Eu3+ and BaTiO3:Eu3+ are presented. Nanocrystalline SrTiO3 and BaTiO3 samples with crystallite sizes about 25–50 nm were produced by the sol‐gel process. The Eu3+ 5D0,1 → 7Fn fluorescence spectra were studied. Time‐resolved fluorescence spectra enabled to separate different kinds of Eu3+ centers in BaTiO3 samples. Fluorescence spectroscopy of probe Eu3+ ions was used to detect the structural Oh – D4h phase transition in nanocrystalline SrTiO3. The Eu3+ excited states lifetimes were studied in a wide temperature range and the effects of modified refractive index of the media on radiative transitions were observed. The study of ferroelectric C4v – Oh phase transition in nanocrystalline BaTiO3 with optical second harmonic generation technique revealed remarkable hysteresis in the temperature dependence of the second harmonic intensity. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
O– bound polarons in oxide materials
Authors: Schirmer O. F. 
Published: March 2007

AbstractThe optical absorption of holes, self‐trapped at one of the equivalent O2– sites next to acceptor defects in crystalline oxide materials, is treated. The holes are localized by lattice distortion, forming small polarons with typical stabilization energies EP of 1 eV. The light‐induced hole transfer from an initial O– site to an equivalent O2– neighbour occurs under Franck‐Condon conditions, leading to the widest possible homogeneous absorption bands, having high oscillator strength, typically 0.1, and peak energies between 8/3 EP and 1 EP, for 4 up to 12 equivalent neighbours. The basic absorption features, including characteristic excited state tunnelling splittings, are exemplified with representative defects of high point symmetry. Such polarons arise in numerous materials after excitation by light or ionizing radiation. They play important roles as sources of coloration in non‐linear optic and photorefractive compounds, gemstones, as acceptor defects in oxide semiconductors and as catalytic agents, if at a surface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Radiation‐induced defects in chalcogenide glasses characterized by combined optical spectroscopy, XPS and PALS methods
Authors: Shpotyuk O. , Kovalskiy A. , Golovchak R. , Zurawska A. , Jain H. 
Published: March 2007

AbstractTemperature‐dependent optical absorption spectroscopy, high‐resolution X‐ray photoelectron spectroscopy and positron annihilation lifetimes spectroscopy are utilized to understand radiation‐induced changes in Ge–Sb–S chalcogenide glasses. Theoretically predicted topological scheme of γ‐induced coordination defect formation in stoichiometric Ge23.5Sb11.8S64.7 glass composition is supported by these measurements. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetism due to defects/oxygen vacancies in HfO2 thin films
Authors: Hong Nguyen Hoa 
Published: March 2007

AbstractRoom temperature ferromagnetism with a large magnetic moment was observed in un‐doped HfO2 films grown on Yttrium Stabilized Zirconia substrates. It is known that neither Hf4+ nor O2– is magnetic. On the other hand, HfO2 bulk is clearly diamagnetic. Since it is certain that there is no contamination in any substrate, it is not possible to attribute such a large magnetic moment to impurities. Certainly thin film form, which might create necessary defects and/or oxygen vacancies, must be the main reason for this un‐doped insulating oxide to become ferromagnetic. Filling up oxygen vacancies can reduce the magnetic moment enormously, and at some critical point, can destroy the ferromagnetic ordering completely. This confirms the assumption that magnetism in HfO2 thin films originates from defects and/or oxygen vacancies. Defects seem to be mostly located at the interface between the film and the substrate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)