0000000000036967
AUTHOR
Nina Mironova-ulmane
showing 59 related works from this author
A comprehensive study of structure and properties of nanocrystalline zinc peroxide
2022
Abstract Nanocrystalline zinc peroxide (nano-ZnO2) was synthesized through a hydrothermal process and comprehensively studied using several experimental techniques. Its crystal structure was characterized by X-ray diffraction, and the average crystallite size of 22 nm was estimated by Rietveld refinement. The temperature-dependent local environment around zinc atoms was reconstructed using reverse Monte Carlo (RMC) analysis from the Zn K-edge X-ray absorption spectra. The indirect band gap of about 4.6 eV was found using optical absorption spectroscopy. Lattice dynamics of nano-ZnO2 was studied by infrared and Raman spectroscopy. In situ Raman measurements indicate the stability of nano-ZnO…
<title>Micro-Raman scattering and infrared spectra of hemoglobin</title>
2008
Confocal micro-Raman and FT-IR spectroscopies have been used for detection of radiation influence of hemoglobin of patients examined by radio-isotopes diagnosis (Tc99m). After irradiation we observed some little changes of the Raman scattering bands which connected with out of plane porphyrine bending vibrations, also we observed additional band due to methemoglobin. Radiation of blood lead to the transition from hemoglobin (Fe2+) to methemoglobin (Fe3+) with a delocalization of iron from porphyrine plane. It was shown that FT-IR spectra indicate the radiation effects on hemoglobin.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is per…
Formation of complex defects in Mn c Mg 1–c O and Ni c Mg 1–c O single solid solution
2005
The results of investigation of the fast neutron irradiation and thermal treatment on absorption spectra of single solid solution of MncMg1–cO, NicMg1–cO and MgO crystals are presented. It is shown that at impurity ion concentration larger than 0.1 mass.% a probability of formation of aggregate centers consisting of more than three F+- or F-centers is small. After thermal treatment of MncMg1–cO and NicMg1–cO single solid solution irradiated by fast neutrons additional wide bands are observed. We assume that these additional bands belong to complex centers of Mn3+-VMg and Ni3+-VMg. The mechanisms of bands formation are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Excitation and photoluminescence spectra of single- and non-single-phased phosphors based on LaInO3 doped with Dy3+, Ho3+ activators and Sb3+ probabl…
2017
Abstract Single-phased La 0.95 Ln 0.05 InO 3 ( Ln – Dy, Ho), La 0.90 Dy 0.05 Ho 0.05 InO 3 , LaInO 3 ceramic samples as well as the La 0.95 Ln 0.05 In 0.98 Sb 0.02 O 3 ( Ln – Dy, Ho), La 0.90 Dy 0.05 Ho 0.05 In 0.98 Sb 0.02 O 3 , LaIn 0.98 Sb 0.02 O 3 samples with additional impurity LaSbO 3 phase were prepared by solid-state reactions method. Their excitation and photoluminescence (PL) spectra were measured at room temperature. It was established that PL bands intensity of spectra obtained for samples of nominal composition La 0.95 Dy 0.05 In 0.98 Sb 0.02 O 3 , La 0.95 Ho 0.05 In 0.98 Sb 0.02 O 3 , La 0.90 Dy 0.05 Ho 0.05 In 0.98 Sb 0.02 O 3 is much higher than that of single-phase La 0.95…
Optical Properties of Natural and Synthetic Beryl Crystals
2015
The results of investigation of photoluminescence and UV-Visible absorption spectra of natural beryl crystals from Ural Mountains before and after fast neutron irradiation and synthetic crystal grown in Belarus and Russia are presented. Photoluminescence (PL) spectra of synthetic beryl crystals contain a broad band with maxima 740 nm excited both by UV light (λex = 260 nm, 271 nm) and laser excitation (λex =263 nm). This band is connected with Fe 2+ ions. The temperature lowering down to 8 K leads to appearance of narrow lines in the 680 - 720 nm regions. Emission lines observed in the luminescence spectra are connected with electron transition 2 Eg→ 4 A2g of the Cr 3+ ions: R-lines (682.5 …
The study of correlation between microstructure of ferrites and their complex permeability spectra
2013
Theoretical model for complex permeability of polycrystalline ferrite (based on effects arising from realities of typical microstructure of sample) is correlated with experimental data. In the case of NiZn-ferrites there is observed a close agreement with the model and the data; for samples of MnZn-ferrites this agreement is only for small-sized cores; for bigger ones the dimensional effects (dimensional resonance) appear and the model cease to be valid.
Studies of TiO<sub>2</sub> Ceramics Structure after Thermal Treatment at Different Conditions
2014
The present work describes results of investigation of structural characteristics of TiO2 ceramics, depending on temperature and thermal treatment conditions by using a variety of characterization techniques. TiO2 ceramics was prepared by extrusion method and developed as a material for electrodes for innovative water treatment technologies. It was shown that non-stoichiometric phase TiO1.95 was observed after thermal treatment of TiO2 ceramics under high vacuum conditions.
<title>Influence of radiation defects on exciton-magnon interactions in nickel oxide</title>
2005
Influence of radiation defects on the optical absorption spectrum of nickel oxide (NiO) was studied at 6 K in the near-IR energy range of 7750-8300 cm-1 corresponding to the magnetic-dipole transition 3A 2g(F )->3T 2g(F ) at nickel sites. NiO single crystals grown by the method of chemical transport reactions on the MgO(100) substrates were irradiated by the neutron fluences up to 5x1018 cm-2. Two sharp lines were observed at the low-energy side of the band: the peak at 7805 cm-1 is assigned to the pure exciton transition, whereas the peak at 7845 cm-1, to the exciton-magnon excitation that occurs at the Brillouin zone-center (BZC). An increase of the defect concentration at higher fluences…
Optical absorption and Raman studies of neutron-irradiated Gd3Ga5O12 single crystals
2018
Abstract In this work we have performed a comparative analysis of optical absorption and micro-Raman spectra for series of Gd3Ga5O12 (GGG) single crystals irradiated by fast neutrons with fluences from 1016 n/cm2 to 1018 n/cm2. It was found that the optical absorption spectra of non-irradiated Czochralski grown GGG consist of the relatively narrow lines in the UV spectral range related to the 4f–4f transitions in Gd3+. Transitions from the 6S7/2 ground state to the 6P, 6J and 6D states in a Gd3+ cation are clearly detected. For a GGG crystal containing Ca impurity ions, additional absorption band at 350 nm is observed, and it is tentatively ascribed to oxygen vacancies associated with Ca im…
Structural disorder and electronic hybridization in NicMg1−cO solid solutions probed by XANES at the oxygen K edge
2007
A series of NicMg1−cO solid solutions has been studied for the first time looking at the structural disorder by means of x-ray absorption near-edge-structure (XANES) spectroscopy at the oxygen K edge. The experimental XANES signals were analysed within the full multiple scattering formalism and were interpreted taking into account clusters of up to 15 coordination shells around an absorbing oxygen atom. The substitution of nickel atoms by magnesium atoms results in a dramatic decrease of the empty density of states in the conduction band close to the Fermi level due to an exchange of the 3d(Ni)–2p(O) interaction with 3p(Mg)–2p(O). Besides, a simultaneous small decrease of the 3d(Ni)–2p(O) h…
Structural and Magnetic Properties of Nickel Oxide Nanopowders
2010
Structure and magnetic properties of nickel oxide (NiO) nanopowders have been studied by X-ray/neutron diffraction, SQUID magnetometer, and micro-Raman spectroscopy. Our diffraction data indicate that at room temperature all NiO powders are antiferromagnetically ordered and have a rhombohedral (R-3m) phase. The SQUID magnetometry and Raman spectroscopy measurements support the presence of the antiferromagnetic ordering.
Chernobyl Clean-Up Workers: 17 Years of Follow-Up in Latvia
2005
About 5000 Latvian inhabitants took part at clean up works after accident on Chernobyl Nuclear Power Plant during 1986–1991. Clinical follow-up programme showed that clean-up workers having higher morbidity rate compare to the general population with prevalence of poly–symptomatic sicknesses caused by depression of immune system. Dose reconstruction made by Electron Paramagnetic Resonance (EPR) indicated underestimation of officially documented doses by factor 2-10. Blood measurement performed by Inductively Coupled Plasma Mass Spectrometry (ICP MS) indicated elevated concentration of lead, cadmium and thorium. It was assumed that toxic compounds, physical stress, incorporated long-lived ra…
Transient and stable color centers in neutron irradiated MgO
2008
Abstract The transient absorption and luminescence induced by the pulsed electron beam have been investigated in the MgO single crystal containing transition metal ion (Cr, Mn, Fe) impurities and preliminary irradiated by the fast neutrons. It is supposed that the different behavior of the absorption spectra of the MgO samples preliminary irradiated by the different fast neutron fluence is connected with the destruction of the hole centers and with the creation of interstitial protons and the formation of the microphase Mg(OH)2. We assume that the luminescence band at ∼3.2 eV is connected with F+ color centers.
<title>Optical properties of hydrogen-containing MgO crystal</title>
2008
The photoluminescence (PL), its excitation (PLE) and absorption spectra in ultraviolet, visible and infrared (UV-VIS-IR) regions were used to investigate the MgO single crystals irradiated by fast neutrons. It is shown that the photoluminescence band of the MgO crystals at 730 nm belongs to the hydrogen-containing complex centers V-OH-Fe3+, which are transformed during the irradiation with fast neutrons. The behavior of the PL band 730 nm after fast neutron irradiation depends on the iron-chromium concentration. It is found that the fast neutron irradiation produces the interstitial proton H+i and the Mg(OH)2 microphase.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineer…
Optical Properties of Natural and Synthetic Minerals
2015
The results of investigation of optical absorption and photoluminescence (PL) of topaz, beryl and yttrium aluminium garnet crystals doped with different concentrations of transition ions exposed to fast neutron irradiation and electron irradiation are presented. We suppose that irradiation leads to the formation of two types of complex centers: "Me2+-F+ (or F) centre" and complex centers, which consist of a cation vacancy and an impurity (iron, manganese and chromium) ion. Exchange interaction between radiation defects and impurity ions during neutron or electron irradiation gives rise to appearance of additional absorption and luminescence band broadening in investigated crystals.
Oxygen K-edge XANES investigation of NicMg1−cO solid solutions
2005
A series of Ni(c)Mg(1-c)O solid solutions are characterized by means of synchrotron radiation X-ray diffraction and X-ray absorption near-edge-structure spectroscopy at oxygen K-edge (532 eV). A dramatic drop of the pre-edge peak intensity is observed in the Ni(c)Mg(1-c)O system upon dilution. It can be attributed to a decrease of 3d(8)(Ni(2+))-2p(O(2-)) mixing upon dilution with magnesium ions due to a decrease of the number of 3d vacancies as nickel ion is replaced by magnesium ion. Similarly, the decrease of the number of 4s and 4p vacancies also leads to a decrease of 4s4p(Ni(2+))-2p(O(2-)) hybridization, and hence a drop of intensities of features B and C. The features E and F are more…
Crystal field calculations of energy levels of the Ni2+ ions in MgO
2013
Abstract The electronic energy levels of six-fold coordinated Ni 2+ ion in magnesium oxide MgO were calculated using the exchange charge model of crystal field theory. The calculated energetic positions of the Ni 2+ levels match well the experimental spectrum. Inclusion of the spin-orbit (SO) interaction is compulsory to account for the first excited 3 T 2g state fine structure; however, it does not explain why out of four levels arising from the 3 T 2g state, only two are seen in the experimental spectra. One possible explanation to this fact can be advanced by invoking the Jahn–Teller effect.
<title>Raman scattering by phonons and magnons in Ni<formula><inf><roman>c</roman></inf></formula>Mg<for…
2003
ABSTRACT The Raman scattering by phonons and magnons was studied at room temperature in polycrystalline solid solutions NiMg1O and pure NiO. The experimental Raman spectrum of NiO consists of six well resolved bands, whose originis due to the disorder-induced one-phonon scattering (bands at 400 and 500 cm'), two-phonon scattering (bands at 750,900 and 1 100 cm) and two-magnon scattering (band at 1500 cm). In NiMg1O solid solutions, a relative increase ofone-phonon scattering is observed upon a dilution of nickel oxide by magnesium ions: at room temperature, the two-magnon band becomes invisible for c<O.7, whereas the two-phonon contribution disappears at c<O.5. Such behaviour isexplained by…
Template-based synthesis of nickel oxide
2015
Nanocrystalline NiO has been produced using a facile template-based synthesis from nickel nitrate solutions using cellulose as a template. Thus obtained oxides were studied by scanning electron microscopy, x-ray diffraction, Raman scattering spectroscopy, photoluminescence spectroscopy and confocal spectromicroscopy. The filamentary/coral morphology of the samples has been evidenced and is built up of agglomerated nanocrystallites with a size in the range of about 26-36 nm. The presence of two-magnon contribution in Raman scattering spectra suggests the existence of antiferromagnetic ordering at room temperature. Finally, the observed near-infrared photoluminescence band at 850 nm has been …
Radiation displacement defect formation in some complex oxide crystals
2000
The work is devoted to an analysis of the formation processes of radiation displacement defects (RDDs) and color centers (CCs) under irradiation of complex oxide crystals. The results of the displacement process simulation as well as the analysis of the RDDs and CCs accumulation kinetics in some complex oxide crystals are presented. New experimental results on additional absorption spectra induced by neutron irradiation of LiNbO3 (LNO) crystals doped with Fe and Cr and YAlO3 (YAP) crystals doped with Nd and Er as well are presented. Dose dependencies are compared and their peculiarities are discussed. ” 2000 Elsevier Science B.V. All rights reserved.
Magnon and Phonon Excitations in Nanosized NiO
2019
Single-crystal, microcrystalline and nanocrystalline nickel oxides (NiO) have been studied by Raman spectroscopy. A new band at ~200 cm-1 and TO-LO splitting of the band at 350–650 cm-1 have been found in the spectra of single-crystals NiO(100), NiO(110) and NiO(111). The Raman spectra of microcrystalline (1500 nm) and nanocrystalline (13–100 nm) NiO resemble those of the single crystals. They all contain the two-magnon band at 1500 cm-1, indicating that the oxides remain at room temperature in the antiferromagnetic phase. Besides, a new sharp Raman band has been observed at 500 cm-1 in nanocrystalline NiO. Its temperature dependence suggests the magnetic origin of the band, possibly associ…
Radiation Induced Defects in Yttrium Aluminium Perovskite
2000
The yttrium aluminium perovskite single crystals YAlO3 (YAP) doped with rare -earth ions belong to the most prospective materials of solid-state laser engineering. Laser based of YAlO3 crystals have the advantage in comparison with yttrium aluminium garnet (YAG). The main of them consists in anisotropy of optical properties [1], which are stipulated by the low symmetry of orthoaluminate crystals. Continuos wave (CW) laser action at 549.6 nm was achieved in 1% Er:YAP crystal at below 77 K [2]. The YAP:Nd allows to obtain a CW generation at 1079 nm, 1340 nm and 1440 nm [3, 4]. It is known, that the color center can completely suppress laser generation in the crystal.
Influence of diamagnetic impurity on mid‐IR absorption in antiferromagnetic insulator NiO
2005
-1 was studied in polycrystalline Ni c Mg 1-c O solid solutions with c=0.99, 0.98, 0.97, 0.95, 0.90, 0.80, 0.70 and 0.60. The composition and temperature dependences of the absorption suggest that the band has magnetic origin re- lated to simultaneous excitation of two-magnons at the Brillouin-zone boundary and one phonon. -1 in polycrystalline NicMg1-cO solid solutions. Polycrystalline solid solutions NicMg1-cO (c=0.99, 0.98, 0.97, 0.95, 0.90, 0.80, 0.70 and 0.60) were prepared using ceramic technology from the appropriate amounts of aqueous solutions of Mg(NO3)2·6H2O and Ni(NO3)2·6H2O salts, which were mixed and slowly evaporated. The remaining dry 'flakes' were heated up to 500-600 oC to…
Temperature and impurity concentration effects on upconversion luminescence in LaInO3 doped with Er3+
2016
In this paper a novel method for synthesis of LaInO3:Er3+ is reported and upconversion luminescence properties of the synthesized material at different temperatures (9–300 K) are studied. The samples were prepared by co-precipitation and subsequent heat treatment of lanthanum, indium and erbium hydroxides. It is shown that the excitation at 980 nm leads to a strong green upconversion luminescence in the material. At the concentrations above 0.1 mol. % of Er3+ the energy transfer upconversion mechanism of the luminescence becomes evident. Further increase of Er3+ content in the material leads to higher red-to-green upconversion luminescence intensity ratio. The mechanisms responsible for the…
Magnetic Ion Exchange Interactions in NiO—MgO Solid Solutions
2006
In this work, a review of recent experimental data and their interpretation for NicMg1−c O solid solutions is given. In particular, the influence of exchange interactions between Ni2+ ions on the structural, optical, magnetic, and vibrational properties is discussed.
Neutron diffraction study of microstructural and magnetic effects in fine particle NiO powders
2016
Nickel oxide powders with grain sizes ranging from 100 to 1500 nm have been studied by high-resolution neutron diffraction. We have found that the atomic structure, the antiferromagnetic ordering, and the value of the nickel magnetic moments inherent in the bulk material of NiO are still preserved and are nearly independent of the average size of the grains. The sizes of the coherently scattering atomic and magnetic domains were estimated independently owing to a complete separation of the nuclear and magnetic peaks in the neutron diffraction patterns. It is shown that the finite-size and surface disorder effects in particles at the submicron scale have a more pronounced influence on the ma…
Design of siliceous lignins – Novel organic/inorganic hybrid sorbent materials
2009
Novel nanoporous lignin(lignocellulose)/SiO2 hybrid materials were designed using the sol–gel process. X-ray photoelectronic spectroscopy, Fourier transform infrared spectroscopy and 29Si and 13C nuclear magnetic resonance spectroscopy were applied to characterize the hybrids’ surface and bulk structure. Nitrogen and water vapor sorption were used for assessment of porous structure parameters and hydrophobization of matrices, respectively. The efficiency of the hybrid materials obtained was proved by adsorption tests with potential inorganic (Cu2+) and organic (2,4-dichlorophenoxyacetic acid) pollutants.
Excitation and emission spectra of LaInO3-based solid solutions doped with Sm3+, Sb3+
2017
Abstract X-ray analysis showed that all the ceramic samples of La 1- x Sm x InO 3 (0.010≤ x ≤0.025) solid solutions were single-phased but the samples of nominal composition of LaIn 0.98 Sb 0.02 O 3 , La 0.98 Sm 0.02 In 0.98 Sb 0.02 O 3 contained a small amount of impurity phase of LaSbO 3 -based solid solutions. It was established that La 0.98 Sm 0.02 InO 3 solid solution under the excitation of 275 nm and 320 nm exhibits the strongest photoluminescence among La 1- x Sm x InO 3 solid solutions with 0.010≤ x ≤0.025. Photoluminescence bands located in wavelength ranges of 550–580 nm, 585–625 nm and 630–680 nm exhibit 2–3 clear maxima each. According to the locations of these maxima we calcul…
Raman and infrared spectromicroscopy of manganese oxides
2009
Abstract Confocal micro-Raman and micro-FT-IR spectroscopies have been used to probe the phase composition of nominally pure single-crystal MnO and mixed MnO–Mn 3 O 4 samples, grown by the method of chemical transport reactions on MgO(1 0 0) substrate. The presence of spinel Mn 3 O 4 phase has been clearly detected in both samples by Raman and FT-IR spectroscopies. The size of the spinel Mn 3 O 4 phase regions has been estimated to be below 20 μm.
EPR and optical spectroscopy of neutron-irradiated Gd3Ga5O12 single crystals
2020
Abstract In this paper, we have performed comparative analysis of EPR, optical absorption (OA) and luminescence spectra for a series of Gd3Ga5O12 (GGG) single crystals irradiated with fast neutrons with fluencies varied from 1016 to 1020n/cm2. In a crystal irradiated with the maximum neutron fluence, the EPR spectra demonstrated the formation of several paramagnetic defects. In particular, EPR spectrum shows a strong resonance at (effective) g ≈ 1.4 with practically isotropic behavior in the crystal rotation around the [1 1 1] direction (magnetic field being perpendicular to [1 1 1]) and several weaker lines in the g ≈ 1.1–2.6 region, which show more pronounced angular dependences. While th…
Displacement Defect Formation in Complex Oxide Crystals under Irradiation
2000
The work is devoted to an analysis of formation processes of the radiation displacement defects (RDDs) and colour centres (CCs) in complex oxide crystals under irradiation. The calculation results on: the displacement process simulation as well as an analysis of the RDD and CC accumulation kinetics are presented. New experimental results on additional absorption spectra induced by neutron irradiation of LiNbO(3) (LNO) crystals doped with Fe and Cr and YAlO(3) (YAP) crystals doped with Nd and Er as well are presented. Dose dependencies of the additional absorption are compared and their peculiarities are discussed. The obtained results confirm that CCs causing the irradiation induced absorpt…
Radiation effects in Li2B4O7 oxide crystals
2000
Abstract The lithium tetraborate single crystal has been irradiated by neutrons and the optical properties of these crystals are studied. Irradiation induces optical absorption bands at 42 000, 33 000, and 20 000 cm −1 . The intensities of these bands depend on the energy of the neutrons, on the irradiation temperature, and on the presence of an external electric field. An applied electric field induces the displacement of charged particles, creating the micrononhomogeneous regions in the crystal leading to a decrease of the intensities of the absorption bands. It has been established that the irradiation damages not only the surface of the crystal but also the deeper layers.
Luminescence and EPR spectroscopy of neutron-irradiated single crystals of magnesium aluminium spinel
2016
Abstract Neutron irradiated single crystals of stoichiometric MgAl 2 O 4 and MgAl 2 O 4 :Mn 2+ (0.15 wt. %) were studied using the methods of luminescence spectroscopy and versions of electron paramagnetic resonance. In stoichiometric MgAl 2 O 4 :Mn 2+ single crystals, the transition of a part of manganese impurity ions from tetrahedral to octahedral coordination, caused by irradiation with fast fission neutrons, is detected using photoluminescence spectra. This fact confirms the partial inversion of a normal spinel due to neutron-irradiation. Using pulse EPR technique it is shown that an electron in the field of oxygen vacancy (i.e. from neutron-irradiation induced F + centres, which are s…
One‐magnon Raman scattering in Ni c Mg 1–c O solid solutions
2005
The one-magnon Raman scattering was studied for the first time in antiferromagnetic NicMg1–cO solid solutions as a function of temperature and composition. We found that (i) the one-magnon frequency extrapolated to T = 0 K experiences an abrupt change between c = 0.99 and c = 0.9 and (ii) the one-magnon energy for highly diluted nickel oxide vanishes significantly below the Neel temperature. The obtained dependences are compared to the theoretical predictions within the mean field approximation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectroscopic studies of Cr3+ ions in natural single crystal of magnesium aluminate spinel MgAl2O4
2021
Abstract The natural spinel crystal MgAl2O4 containing the Cr3+ ions was studied experimentally and theoretically in this paper. The absorption and emission spectra at room and low temperatures were recorded. The experimental spectroscopic results were aided with the crystal field calculations, which returned the energy level schemes of the Cr3+ ions at the Al sites with the local D3d symmetry. Effects of the trigonal crystal field were clearly seen in the calculated results, which were compared with the experimental spectra to yield a good agreement between both data sets.
Growth and optical properties of transition metal oxides single crystal solid solutions
2007
Abstract NiO, CoO, MnO single crystals and single crystal solid solutions of Ni c Mg 1− c O, Co c Mg 1− c O and Mn c Mg 1− c O were grown by the method of chemical transport reaction (the “sandwich” technique). The nature of the observed absorption and luminescence bands is explained in terms of the electronic transition of bivalent nickel, cobalt and manganese. The fine structure of the observed bands in NiO and MnO are connected to the pure exciton transition and to the exciton-magnon excitation.
Photo-electrical and transport properties of hydrothermal ZnO
2016
We performed the studies of optical, photoelectric, and transport properties of a hydrothermal bulk n-type ZnO crystal by using the contactless optical techniques: photoluminescence, light-induced transient grating, and differential reflectivity. Optical studies revealed bound exciton and defect-related transitions between the donor states (at ∼60 meV and ∼240 meV below the conduction band) and the deep acceptor states (at 0.52 eV above the valence band). The acceptor state was ascribed to VZn, and its thermal activation energy of 0.43 eV was determined. A low value of carrier diffusion coefficient (∼0.1 cm2/s) at low excitations and temperatures up to 800 K was attributed to impact the rec…
Phase Transition in Niobophosphate Glass-Ceramic
2011
Phase transition during crystallization of glass to glass-ceramic in system P2O5-CaO-Nb2O5-Na2O was studied. Several heating rates were compared – 1, 2, 5, 11 and 20°Cmin-1. DTA, XRD, FTIR and Raman analyses were performed. Niobophosphate glass-ceramic is found to form utterly different crystalline phases depending on maximal heating temperature, heating rate and time of maximal temperature maintenance. Crystallization temperatures of the same phases are strongly dependent on heating rate, while crystallinity of obtained phases is not. At lower temperatures poorly crystalline phosphates (Ca3(PO4)2, Ca10Na(PO4)7, Ca2P2O7) and niobates (NaNbO3 and Nb2O5) are identified. At higher temperatures…
Up-conversion and Photoluminescence in Er3+ Single Crystal MgAl-spinel
2015
Abstract Traditional and up-conversion luminescence of MgAl 2 O 4 single crystal doped with erbium ions obtained by the Verneuil method has been investigated. The time resolved spectral measurements of the green and red up-conversion luminescence bands show that a build-up part is present in the up-conversion luminescence kinetics. This means that energy transfer process is involved in the creation of the luminescence. Considering rather small concentration of Er 3+ in the material (0.12 mass %), the expected up-conversion mechanism should be excited state absorption since the average distance between erbium ions is high. The above-mentioned considerations suggest that clustering of the act…
Elaboration and characterization of organic/inorganic hybrid nanoporous material incorporating Keggin-type Mo-Si polyanions
2007
A novel nanoporous (pore size of 11 nm in average, BET surface area of 30 m2/g, pore volume of 300 mm3/g) hybrid inorganic-organic material was synthesized using the solid-phase interaction at room temperature of plant-originated phenylpropanoid polymer lignin and a Keggin-type heteropolyanion [SiMo12O40]4-. The partly reduction of Mo(VI) to Mo(V) and complexes formation between lignin and polyanion have been established by EPR, FT-IR and Raman spectroscopy. The XRD pattern and FT-IR spectrum of the hybrid material and indicates that [SiMo12O40]4- anion maintains the Keggin structure.
Radiation defects and transition ions interaction in magnesium oxide
2007
Abstract The absorption spectra of nickel and manganese doped and pure MgO single crystals were investigated before and after fast neutron irradiation and after annealing. It is shown that the fast neutron irradiation leads to the formation of two types complex center: “Me 2+ –F + (or F) center” and “Me 3+ –V Mg ”. From the behavior of the ∼570 and ∼357 nm absorption bands during annealing the activation energies of the corresponding defects are determined. The obtained activation energy values ( E a
Neutron irradiation influence on magnesium aluminium spinel inversion
2002
Abstract Grown by the Verneuil method MgO · nAl2O3 single crystals and natural spinel crystal have been studied using X-ray diffraction and photoluminescence spectra. The fast neutron irradiation of magnesium aluminium spinel leads to the lattice parameter decrease. The bond lengths of Mg–O and Al–O vary with the u-parameter and the lattice parameter. On the other hand, the bond lengths are related with the inversion parameter. Using changes of the lattice parameter during irradiation we have calculated the inversion parameter, which is 15–20%. In the luminescence spectra, the fast neutron radiation (fluence 1016 cm−2) produces an increase in the intensity ratio of the N- to R-lines by 5–20…
Determination of methemoglobin in human blood after ionising radiation by EPR
2015
In the present work presents results of investigations of radiation influence on blood of patients examined by radio-isotopes diagnosis (Tc 99m ), blood of Chernobyl clean-up workers and human blood irradiated by LINAC using Electron Paramagnetic Resonance (EPR). The EPR spectroscopy reveals information on electronic states of transition metal ions, particularly Fe 3+ in different spin states. It is shown that EPR spectra of blood of patients before examination has signal from metal-protein transferrin (g=4.3) and after administration of radio- isotope proves signal of Fe 3+ (methemaglobin) in the high spin state (g=6.0). The EPR spectra of Chernobyl liquidator display number of signals inc…
Role of paramagnetic polyconjugated clusters in lignin antioxidant activity(in vitro)
2012
Using physico-chemical methods (EPR, SEC, Py-GC/MS and UV/VIS spectroscopy) and wet chemical analysis, the characteristics of 6 hardwood lignins in terms of functionality, molecular weight and composition of lignin substructures were determined and considered together with the results of DPPH•, ABTS•+ and O2•− antioxidant assays with the aim to understand the relationships governing antioxidant properties of lignin. The strong positive linear correlation between lignin antioxidant capacity in the three assays used and the extent of conjugation of paramagnetic polyconjugated clusters in lignin macromolecules was found. The biological activity of the most active alkaline lignins was assessed …
Retrospective dosimetry for Latvian workers at Chernobyl.
2001
Between 1986 and 1991 approximately 6500 Latvian inhabitants were recruited for clean-up work at the Chernobyl nuclear power plant. Their absorbed doses are usually unknown, because less than half of them had their external exposure officially documented. Clinical investigations show a high morbidity rate for these clean-up workers when compared with that of the general population. In order to understand the causes of their diseases and the impact of ionising radiation, electron spin resonance (ESR) has been used to measure the absorbed doses in human tooth enamel. The doses estimated by ESR were between two and three times higher than previously documented and are in accord with the result…
Low-temperature studies of Cr 3+ ions in natural and neutron-irradiated g-Al spinel
2020
This study was supported by a grant from Latvian Council of Science (agreement No. LZP-2018/1-0214).
Behavior of one-magnon frequency in antiferromagneticNicMg1−cOsolid solutions
2005
The one-magnon scattering was studied in antiferromagnetic ${\mathrm{Ni}}_{c}{\mathrm{Mg}}_{1\ensuremath{-}c}\mathrm{O}$ solid solutions. We observed unpredicted behavior of both temperature and composition dependences of one-magnon excitation energies. First, the abrupt change of the one-magnon frequency by $7--8\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ occurs between $c=0.98$ and $c=0.9$ in the limit of $T\ensuremath{\rightarrow}0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Second, upon increasing temperature, the one-magnon energy for highly diluted nickel oxide vanishes significantly below the N\'eel temperature.
Neutron scattering study of structural and magnetic size effects in NiO
2013
Nickel oxide powders with the grain size of 13–1500 nm have been studied by neutron scattering, scanning electron microscopy and vibrating sample magnetometry. We have found that the atomic structure and the antiferromagnetic ordering are nearly independent of the average size of grains. The existence of the uncompensated spins in nanoparticles with the grain size below 100 nm has been detected.
Polarisation dependent Raman study of single-crystal nickel oxide
2011
Abstract The magnetic domain structure and Raman scattering have been studied in NiO single-crystals with three different (100), (110) and (111) orientations. Twin-domain structure was observed in NiO(100) and NiO(110) single-crystals using cross-polarized optical microscopy. We found that the ratio of the two-magnon (at 1500 cm−1) to the two-phonon (2LO, at 1100 cm−1) Raman bands intensity is sensitive in a particular way to the type of the twin-domain pattern.
The Optical And Epr Spectra of Fe(2+) and Fe(3+) Ions in the Blood of the Chernobyl Clean-Up Worker
2007
Electron paramagnetic resonance (EPR) and optical absorption studies of blood were provided for the group of Chernobyl’s NPP accident clean-up workers examined in the Center of Occupational and Radiological medicine of P.Stradins Clinical hospital of Medical Academy of Latvia. The EPR spectra for blood have been studied at low temperature. It is shown that in blood the ion Fe3+ of methemaglobin is in low-spin state with g = 2.3 and in the high spin state with g=6. We observed the additional absorption bands 500 nm (shoulder) and 630 nm in absorption spectra of blood of Chernobyl clean-up worker who has erythrocytosis.
Structure and Phase Changes in Natural and Synthetic Magnesium Aluminum Spinel
2015
Natural spinel crystals from Ural and Pamir deposits and synthetic magnesium aluminium spinel single crystals with different stoichiometry (MgO.nAl2O3 ) grown by Verneuil method were used. The photoluminescence (PL), its excitation (PLE) and optical absorption of stoichiometric and nonstoichiometric magnesium aluminium spinel crystals containing the chromium and manganese ions and defects produced by fast neutron irradiation( fluence up to 1020cm-2, E&gt;0.1 MeV) are investigated. The broadening of R- and N-lines takes place in synthetic stoichiometric spinel. Structure of synthetic nonstoichiometric spinels (n&gt;1) has to be more disordered, since in addition to the site exchange …
Structure of nanoporous carbon materials for supercapacitors
2012
Activated carbons with highly developed porous structure and nanosized pores (8 - 11 A) were prepared from alder wood using thermochemical activation method with sodium hydroxide. Properties of the obtained activated carbons were examined by benzene and nitrogen sorption, X-Ray diffraction and Raman spectroscopy. Tests of activated carbons as electrodes in supercapacitors were performed as well. It was found that specific surface area of above mentioned activated carbons was 1800 m 2 /g (Dubinin - Radushkevich). Raman spectroscopy demonstrated the presence of ordered and disordered structures of graphite origin. The performance of activated carbons as electrodes in supercapacitors have show…
Highly Porous Wood Based Carbon Materials for Supercapacitors
2015
Wood based activated carbons synthesized by two-stage thermocatalytical synthesis with NaOH activator were studied and used as supercapacitor electrodes (sulphuric acid electrolyte). Porous structure and electrochemical properties of carbons vs synthesis conditions were assessed. It was found that there are correlations between carbons synthesis variables, their porosity and supercapacitors functional characteristics. At the temperature 600 o C and activator/precursor ratio 1.25 porosity decreased, however energy capacitance of supercapacitor increased calculating on elementary cell mass.
Dielectric properties of PMN+2%Li 2 O at low frequencies
2012
The reported study is focused on effects of the admixture of lithium (2% Li2O) on the low-frequency dielectric response in lead magnesium niobate ceramics over the 100 -300 K range of temperature. The obtained results reveal an essential thermal broadening of the e′(ν) spectra specific to relaxor ferroelectrics. Dispersion Δe′ = e′1Hz-e′1kHz and values of e′′(ν) in lead magnesium niobate ceramics containing Li are well described by the Cole-Cole equation at temperatures below the e′(T) maximum. Based on the analysis of the experimental data admixture of lithium is suggested to promote formation of domains in lead magnesium niobate ceramics (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Fast-neutron-induced and as-grown structural defects in magnesium aluminate spinel crystals with different stoichiometry
2019
Abstract Several hole-type paramagnetic defects (a hole localized at a regular oxygen ion near charged structural defect/defects) have been revealed in fast-neutron-irradiated MgO⋅2.5Al2O3 single crystals using the EPR method. Three of them (a dominant V1 and small amount of V2 and V22) were recently revealed in a neutron-irradiated stoichiometric MgAl2O4, while a novel V4 center, ascribed to a hole in a form of O− ion nearby a complex of a magnesium vacancy and a positively charged antisite defect (V4 ≡ O–‑VMg‑Al|Mg), was created by fast neutrons only in a nonstoichiometric single crystal. The pulse annealing of the EPR signal of these centers was compared to that of radiation induced opti…
Optical Properties of Irradiated Topaz Crystals
2015
The results of an investigation of UV-Visible absorption and photoluminescence spectra of colorless topaz before and after neutron irradiation, natural blue topaz from Ukraine, and yellow topaz are presented. We assume that the absorption band ~ 620 nm and broad emission band 300-700 nm in topaz crystals are associated with exchange interaction between a radiation defect (anion vacancies, which capture one or two electrons) and impurity ions Cr 3+ , Fe 3+ and Mn 2+ .
Raman scattering in nanosized nickel oxide NiO
2007
Magnetic ordering in nanosized (100 and 1500 nm) nickel oxide NiO powders, prepared by the plasma synthesis method, was studied using Raman scattering spectroscopy in a wide range of temperatures from 10 to 300 K. It was observed that the intensity of two- magnon band decreases rapidly for smaller crystallites size. This effect is attributed to a decrease of antiferromagnetic spin correlations and leads to the antiferromagnetic-to- paramagnetic phase transition .
Luminescence and optical spectroscopy of charge transfer processes in solid solutions Ni Mg1−O and Ni Zn1−O
2016
Abstract In this work photoluminescence spectra for Ni c Mg 1− c O and Ni x Zn 1− x O solid solutions with the rock-salt crystal structure were obtained under synchrotron radiation excitation. Periodical peaks in the photoluminescence excitation spectrum of Ni c Mg 1− c O ( c =0.008) have been discovered for a wide-gap oxide doped with 3d impurities for the first time. They can be considered as LO phonon repetitions of the narrow zero phonon line resulted from the optical transitions into the p–d charge transfer exciton [d 9 h] state. A close coincidence in energy of different peculiarities in the optical absorption and photoluminescence excitation spectra for the Ni c Mg 1− c O and Ni x Zn…
Synthesis and Vibration Spectroscopy of Nano-Sized Manganese Oxides
2018
The present study has been supported by the Latvian National Research Program IMIS2. One of us, IS, was supported by MES RF RFMEFI61615X0064.