bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ionic and electronic defects in a‐BaTiO3 thin films studied by transient and steady state conductivity measurements
Authors: El Kamel F. , Gonon P. , Yangui B. , Jomni F. 
Published: March 2007

AbstractConduction mechanisms in BaTiO3 films deposited at low temperatures on Cu‐electrodes have been investigated in transient and steady regimes as a function of temperatures and electric field. This work aims to identify possible defects which govern the leakage current. Electrical measurements reveal that Space Charge Limited Current (SCLC) constitutes the main leakage mechanism in both the transient and the steady regimes. Based on the theory of SCLC, two types of defects can be detected. At higher temperatures, oxygen vacancies constitute the main defects which migrate across the film to generate an ionic leakage current. Diffusion of these defects is thermally activated with an activation energy around 1 eV. Moreover, at lower temperatures the J ‐E measurements reveals the presence of a discrete set of shallow traps at 0.45 eV below the conduction band with an effective density of 4 × 1022 m–3. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron‐phonon interaction in Er and Dy doped YAl3(BO3)4 single crystals
Authors: Mazzera M. , Baraldi A. , Capelletti R. , Beregi E. , Földvári I. 
Published: March 2007

AbstractIn the present work high resolution Fourier Transform spectroscopy is applied to monitor the electron‐phonon (e–‐ph) interaction in YAB single crystals doped with trivalent Er and Dy ions. The electron‐phonon coupling is analysed by monitoring the shape, width, and position of the zero‐phonon lines induced by Er3+. The shift and broadening with temperature increasing are discussed in the framework of the two‐phonon Raman scattering. The e–‐ph interaction is revealed even by the presence, in the absorption spectra of Er and Dy doped YAB crystals, of new weak lines attributed to vibronic transitions. The energy separations between the vibronic and the ZP lines are compared with IR‐active modes measured on YAB crystals. Boron isotopic effects are also put in evidence. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High resolution absorption spectroscopy on rare earth doped insulating materials: BaY2F8 and YAl3(BO3)4 single crystals and sol‐gel silica glasses
Authors: Baraldi A. , Capelletti R. , Magnani N. , Mazzera M. 
Published: March 2007

AbstractThe electronic energy transitions occurring in rare earth (RE) ions within the intraconfigurational 4f shell give rise at low temperature to very narrow absorption lines. Even if the shielded 4f shells are weakly coupled with the surrounding, the RE electronic configuration represents a very sensitive probe for the crystal field at the impurity site. Temperature dependent high‐resolution absorption measurements can then provide a deep insight into the local crystal field and into the ion interaction with the host lattice.Examples of high resolution Fourier transform spectroscopy measurements performed both on crystalline materials (namely fluoride and borate single crystals) and on sol‐gel silica glasses containing nanocrystals are provided and discussed. Correlated analysis based on experimental data and crystal‐field calculations is presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Defect structure behaviour in metal halides
Authors: Levy Mark R. , Patel Ankoor , Stanek Christopher R. , McClellan Ken , Grimes Robin W. 
Published: March 2007

AbstractDefects in halide materials have been investigated using atomistic scale computer simulation. These defects are important in controlling a number of key materials properties. Rare‐earth halides (REX3 with X= F, Cl, Br, I) are currently being considered as scintillator hosts. Here we begin by investigating the fluorides (REF3). These materials undergo an experimentally observed structural change as a function of RE cation radius. We have reproduced this structural variation with an atomistic model. In order to optimise scintillator properties, the intrinsic defect mechanisms need to be assessed as such defects act as performance limiting trap sites. The predictions made are interpreted as a function of the host cation radius in order to reveal structural trends. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High resolution FT absorption study of holmium doped yttrium aluminum borate single crystals
Authors: Baraldi A. , Földvári I. , Capelletti R. , Magnani N. , Mazzera M. , Beregi E. 
Published: March 2007

AbstractHigh resolution FT spectroscopy has been applied to investigate a YAB: Ho3+ (1 mol%) single crystal, grown by the top‐seeded flux method, in the wave number 4000–25000 cm–1 and temperature 9–300 K ranges, respectively. The complex Ho3+ (4f10) non‐Kramers ion transitions from the ground 5I8 to the excited 5I7, 5I6, 5I5, 5I4, 5F5, 5S2, 5F4, 5F3, 5F2, 3K8, 5F1 + 5G6, and 5G5 manifolds were analyzed. The low‐temperature high resolution spectra of the investigated manifolds show for many electronic transitions hyperfine structures related to the Ho3+ nuclear magnetic moment. The experimental data are fitted by a single ion Hamiltonian and the crystal field parameters are obtained. The results are compared with those previously published for other rare earths in the same matrix. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of structural evolution in Ce‐ and Nd‐doped aluminoborosilicate glasses under β‐irradiation
Authors: Malchukova E. , Boizot B. , Petite G. , Ghaleb D. 
Published: March 2007

AbstractThe structural changes in aluminoborosilicate glasses under β‐irradiation as a function of rare earth oxide content and the dose have been studied using Electron Paramagnetic Resonance (EPR) and luminescence spectroscopies. The EPR measurements at helium temperature (4 K) showed that β‐irradiation affects valence state of cerium ions. According to concentration and dose dependences, the line with g ∼ 2.89 can be attributed to paramagnetic Ce3+ ions resulting from Ce4+ reduction under irradiation. The effect of CeO2 content leads to the modifications of the EPR signal of defects at helium and the change in the relative proportion of electron and hole defects with the increase of the cerium doping level at room temperature. We observed also a decrease of the defect concentration as a function of the Nd doping into these glass compositions but by two orders less than for Ce‐doped samples. Exposure to irradiation induced the appearance of a non‐resolved EPR band in the region of defects. We can assume that possible dipolar interaction between Nd3+ ion and hole can result in not typical EPR resonance shape of paramagnetic defects at g ∼ 2. Moreover, estimation of the ratio between splitted components of the 4F3/2 – 4I9/2 transition depending on the irradiation dose showed that dose increase leads to increase of this ratio suggesting that the nearest environment of Nd ions is expected to be changed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New aspects of light‐induced charge transport in potassium tantalate crystals doped by copper and iron
Authors: Badalyan A. G. , Azzoni C. B. , Galinetto P. , Mozzati M. C. , Jastrabik L. , Rosa J. , Hrabovsky M. , Syrnikov P. P. , Trepakov V. A. 
Published: March 2007

AbstractThe light‐induced charge transport process in as grown and thermally treated in oxygen atmosphere nominally pure KTaO3 (KTO) single crystals and KTO doped by Cu (KTO:Cu) and Fe (KTO:Fe) were studied by electron paramagnetic resonance (EPR). A sizeable increasing of the EPR signal of Cu2+ centers and reducing for Fe3+ centers was observed under UV illumination (365nm) in the oxidized KTO:Cu and KTO:Fe crystals respectively. This effect is considered as a sequence of the light induced charge exchange between Cu+ and Cu2+, and between Fe3+ and Fe2+ centers. Correlation between temperature dependencies of the EPR signals and photoconductivity was found and discussed too. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase composition and crystallinity of thin lead titanate films
Authors: Sidorkin A. A. , Nesterenko L. P. , Smirnov G. L. , Smirnov A. L. , Ryabtsev S. V. 
Published: March 2007

AbstractLead titanate thin films with high and stable ferroelectric properties were obtained by plasma‐enhanced magnetron sputtering of pure metals. Effects of crystallites orientation, a substrate and grain boundaries on macroscopic ferroelectric properties of thin films were discussed. It was shown, that strong mechanical stresses, related to different thermal expansion of the film and the substrate materials, render determining influence on crystallites orientation in the film and lead to formation of mechanically clamped non‐ferroelectric layers in the vicinity of interfaces. The use of Al2O3 as substrate material enables the formation of higher quality PbTiO3 films, as compared to the films on the traditional silicon substrates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relaxation emission of electrons and photons from rare‐gas solids: correlation and competition between TSL and TSEE
Authors: Savchenko E. V. , Khyzhniy I. V. , Gumenchuk G. B. , Ponomaryov A. N. , Bondybey V. E. 
Published: March 2007

AbstractCorrelation studies of thermally stimulated luminescence (TSL) and thermally stimulated exoelectron emission (TSEE) from solid Ar pre‐irradiated with an electron beam are presented. Measurements were performed using different heating modes – step‐wise heating and heating with a constant rate. Influence of pre‐existing defects and dose effect on TSL and TSEE are considered. TSEE active layer is estimated. Correlation between TSL and TSEE phenomena pointing to the common primary process – release of electrons from the same kind of traps, is clearly demonstrated. Competition between TSL and TSEE is discussed. It was found that TSEE predominates at low temperatures and in the range of sublimation. Long time irradiation suppressed the total yield of exoelectrons. The part of chemiluminescent reactions in relaxation cascades is elucidated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photon‐stimulated charge recombination and exoelectron emission from pre‐irradiated solid Ar
Authors: Gumenchuk G. B. , Bludov A. M. , Belov A. G. , Ponomaryov A. N. , Bondybey V. E. , Savchenko E. V. 
Published: March 2007

AbstractSpatially separated stable charge centers – self‐trapped holes, trapped electrons, dopant ionic centers and radicals were generated in an Ar matrix doped with Xe and N2 by a low energy electron beam. A combination of the cathodoluminescence (CL) with the photon‐stimulated luminescence (PSL) and photon‐stimulated exoelectron emission (PSEE) methods was used to monitor center formation and selected relaxation channels – charge recombination reactions and exoelectron emission. PSEE from pre‐irradiated Ar samples was registered simultaneously with N line emission. Vacuum ultraviolet (VUV) intrinsic and extrinsic recombination luminescence from pre‐irradiated samples has been detected to confirm the suggested relaxation path of the stored energy. An afterglow of the N line can be considered as an internal source of photons which releases electrons from the traps and being a triggering mechanism of relaxation processes: (i) – exoelectron emission, (ii) – radiative recombination of charge species. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Soft X‐ray excitation of luminescence in wide bandgap crystals doped with rare‐earth ions
Authors: Meltchakov E. , Vidal B. , Kamenskikh I. , Vasil'ev A. N. , Belsky A. , Dujardin C. , Nannarone S. , Pedio M. , Giglia A. , Mahne N. , Coreno M. , de Simone M. , Danailov M. 
Published: March 2007

AbstractLuminescence excitation spectra of wide bandgap oxide crystals were measured in the soft X‐ray range of excitation (300–750 eV) at the BEAR beamline of the electron storage ring Elettra (Trieste). We give a special attention to changes of the light yield in the vicinity of the absorption K‐edge of oxygen. The excitation spectra of two well‐known scintillators YAG‐Yb and LuAP‐Ce (chemical formulae are Y3Al5O12:Yb (15%) and LuAlO5:Ce (0.4%)) reveal a non‐proportional change of the quantum yield and a different response to the jump of absorption coefficient at the 1sO edge for certain emission bands. The analysis of experimental data shows that both the surface loss and interaction effects between secondary electronic excitations (EEs) can influence the energy conversion process in crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oxygen transport mechanisms in REAlO3 scintillators
Authors: Stanek C. R. , Uberuaga B. P. , McClellan K. J. , Levy M. R. , Grimes R. W. 
Published: March 2007

AbstractThe performance of oxide scintillators often suffers from phenomena related to the existence of point defects. Thus, if deleterious defects are removed, it follows that scintillator performance will improve. In the case of REAlO3 perovskites, the oxygen vacancy has been identified as the predominant electron trap site. Previous empirical efforts to minimize the concentration of this particular defect through aliovalent doping have been successful. Here we discuss the results of atomic scale simulations that provide important detail regarding the mechanism by which the oxygen vacancy concentration is reduced. Specifically, we describe the complex mobility of oxygen vacancies and interstitials, which governs the recombination of these defects. The results of these simulations will aid in the synthesis of optimized scintillation materials. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multifrequency spectroscopy of laser active centers Nd3+ and Yb3+ in nearly stoichiometric LiNbO3
Authors: Malovichko G. , Bratus V. , Munro M. , Kokanyan E. , Okulov S. , Grachev V. 
Published: March 2007

AbstractLithium niobate crystals doped with neodymium and ytterbium were studied with the help of the electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and optical absorption. Tremendous narrowing of magnetic resonance lines in nearly stoichiometric samples in comparison with congruent ones allowed us to distinguish four non‐equivalent centers (NEC) of Nd3+ and five NEC of Yb3+, as well as line splitting caused by hyperfine interaction of neodymium electrons with nuclear spins of magnetic isotopes 143Nd, 145Nd, 171Yb and 173Yb. It was shown that some of the centers has axial C3 symmetry, whereas all others have lowest C1 symmetry due to presence of intrinsic defects or/and charge compensation defects in the near neighborhood of Nd3+ and Yb3+. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of defect‐trap‐related europium sites in gallium nitride
Authors: Fleischman Z. , Tafon P. S. , Dierolf V. , Munasinghe C. , Steckl A. J. 
Published: March 2007

AbstractWe performed site‐selective combined excitation‐emission spectroscopy (CEES) studies on Eu‐doped GaN layers grown using Interrupted Growth Epitaxy (IGE). We identified numerous Eu3+ incorporation sites, which exhibit different relative emission intensities as the growth conditions are varied. We found defecttrap related Eu sites that can be excited over a wide spectral range and that dominate the photoluminescence spectra for above‐bandgap excitation. Spectra obtained through above‐bandgap excitation, which simulates EL operation, are identical to the emission spectra of these defect‐trap related sites, indicating that these particular Eu ions would be the major contributors to electroluminescent (EL) emission in these samples. In resonant excitation, however, the emission from these sites is rather weak suggesting that these are minority sites. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Site‐selective studies of erbium ion defects in thermally grown silicon oxides
Authors: Fleischman Z. , Dierolf V. , Dong Z. , Zhang Y. , White M. , Pafchek R. , Webster M. , Koch T. 
Published: March 2007

AbstractUsing the site‐selective technique of combined excitation emission spectroscopy (CEES), we have studied a variety of Er‐doped silicon oxide layers and silicon‐rich oxide (SRO) layers which contain silicon nanocrystals. With this technique we identi.ed Er cluster defect sites which are created during thermal annealing and which dominate at high Er concentrations. We investigate the role that Si nanocrystals play in the relative abundance of these cluster sites. In attempts to reduce this clustering effect, we observed mixed results by modifying the growth procedure such that Er is already present in the silicon during oxide growth. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of Cu ions on the photo‐transport properties in KTaO3:(Cu,V) single crystals
Authors: Rossella F. , Perucchini L. , Galinetto P. , Samoggia G. , Mozzati M. C. , Azzoni C. B. , Badalyan A. G. , Trepakov V. A. , Syrnikov P. P. 
Published: March 2007

AbstractPhotoconductivity kinetics, temperature dependence and excitation spectra were measured in the intervals 15‐300 K and 2‐4.2 eV in KTaO3:(Cu,V) single crystals processed by oxidation/reduction treatments. The kinetics, excited by band‐gap excitation, present very slow saturation times, while faster time responses were observed using excitation below the band‐gap. The oxidized crystal exhibited higher photoconductivity when Elight > 3 eV. Linear dependence on light intensity was measured, suggesting one center recombination processes. Optical absorption at room temperature was checked as complementary information. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermoluminescence, photoluminescence and optically stimulated luminescence properties of X‐ray irradiated RbMgF3:Mn2+
Authors: Dotzler C. J. , Williams G. V. M. , Edgar A. 
Published: March 2007

AbstractOptically stimulated luminescence (OSL) is observed after x‐ray irradiation in Mn2+ doped RbMgF3 polycrystalline samples over a wide wavelength range in the near UV and with a stimulation maximum near 350 nm. The OSL emission occurs by relaxation from the first excited state to the ground state of Mn2+. It is possible that one of the electron traps can be attributed to an F ‐center. However, thermoluminescence (TL) measurements show that there are at least 5 defect centers in this compound. Sintered polycrystalline samples have a higher OSL intensity when compared with the as‐made samples. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient and near‐edge absorption in YVO4 crystals
Authors: Millers D. , Yochum H. M. , Pankratov V. , Potera P. , Grigorjeva L. 
Published: March 2007

AbstractThe process of near‐edge absorption annealing in air was studied up to 1500C in YVO4. In this annealing process, two stages with activation energies of 0.16 eV and 0.38 eV were obtained. (Should combine to make this one paragraph)In addition to the annealing study, the transient absorption induced by pulsed electron beam excitation (270 keV, 8 ns) was completed on a set of YVO4 samples with different near‐edge absorption levels in the spectral region 3.2‐3.5 eV. The spectral range from ∼1.25 eV up to 3.0 eV is covered by strong transient absorption. Transient absorption spectra show at least three broad overlapping bands (∼1.3 eV, ∼2.0 eV and ∼3.0 eV). The 3 eV peak position is close to the near‐edge absorption band and correlation between transient absorption bands and absorption due to stable colour centers was studied. It is suggested that absorption bands at ∼1.3 eV and ∼2.0 eV are due to electron and hole polarons, correspondingly. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical investigation of tungstate crystals with point defects
Authors: Hizhnyi Yu. A. , Nikolaenko T. N. , Nedilko S. G. 
Published: March 2007

AbstractThe electronic structure of WO66––Zn2+ complex in ZnWO4 crystal is calculated by the configuration interaction method in embedded cluster approach. The dependencies of energies of the electronic states of WO66––Zn2+ centre on displacements of atomic coordinates that model vibrations of WO66– group are calculated. Spectrum of ZnWO4 crystal intrinsic emission is explained on the basis of obtained results. The influence of nearby VO and VZn vacancies on electronic structure of WO66––Zn2+ complex is studied. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal and photo stimulated luminescence of F‐centre aggregates in electron and X‐ray irradiated KCl:Eu2+ polycrystalline films
Authors: Aceves R. , Gracia‐Jiménez J. M. , Silva‐González R. , Tabares‐Muñoz C. 
Published: March 2007

AbstractThe thermoluminescence (TL) and photostimulated luminescence (PSL) of KCl:Eu2+ films irradiated with low energy electrons, β‐ and X‐rays have been investigated. The TL glow curves have been related to irradiation induced defects in both the film and substrate accordingly to the penetration depth of radiation. Measurements of photransferred TL (PTTL) suggested the F, FZ and F‐aggregates formation by X‐ray and low energy electrons. The photostimulation of a previously irradiated sample with 560, 640 and 655 nm have revealed the F2 and F3 defects related infrared (IR) luminescence. An additional PSL band peaked around 1380 nm was observed by photostimulation with 640 nm which could be related to F type defects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Co‐emission of Tb3+ and Eu3+ ions in LiNbO3:Tb 3+, Eu 3+ single crystals
Authors: Alvarez E. R. , Sosa R. F. , Földvári I. , Polgár K. , Péter Á. , Muñoz A. F. 
Published: March 2007

AbstractIn this paper the optical properties (emission and excitation spectra) of Tb3+ and Eu3+ ions in LiNbO3:Tb3+(LNTb), and LiNbO3:Eu3+(LNEu) single crystals, and of Tb3+ and Eu3+ ions in doubly doped LiNbO3:Tb3+,Eu3+ (LNTbEu) are presented, in the 200‐700 nm range at 12 K. The results are discussed and combined with previous observations on the optical properties of LiNbO3:Tb3+(LNTb), LiNbO3:Eu3+ (LNEu) in order to get a better understanding on the nature of the Tb3+→ Eu3+ energy transfer mechanism, observed in our LNTbEu samples. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Common features of thermoluminescence in NaCl and LiF crystals
Authors: Davidson A. T. , Kozakiewicz A. G. , Derry T. E. , Comins J. D. , Suszynska M. , Valberg L. , Townsend P. D. 
Published: March 2007

AbstractWe review our work on the thermoluminescent properties of LiF and NaCl crystals. The role of impurities and their effect on glow curves is considered. A spectral analysis of light emitted at glow peaks suggests some common processes active in the two materials, including intrinsic emission from self trapped excitons near 360 nm wavelengths and impurity enhanced emission near 417 nm wavelengths. The latter may be related to the presence of impurity‐vacancy dipoles in a form which favors TL emission. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Toward control of point defects in lithium fluoride thin layers
Authors: Montereali R. M. , Bonfigli F. , Marolo T. , Mussi V. , Nichelatti E. 
Published: March 2007

AbstractPoint defect formation and stabilization properties, as well as their peculiar spectroscopic characteristics, locally modify the optical properties of insulating materials. Thin layers containing high concentrations of colour centres, hosted in a LiF single crystal and/or a polycrystalline matrix, offer the opportunity to develop innovative light‐emitting photonic devices. Control of all the critical parameters should be required on spatial dimension comparable with the optical wavelengths. Recent developments in laser technologies, electron and particles beam methods, and novel photon sources, have opened a wide range of opportunities. An overview of the most significant advances in this field is provided, with particular emphasis on colour‐centre LiF‐based innovative miniaturised light sources, optical amplifiers and lasers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)