showing 24 related works from this author
Requirements Model of Sociotechnical Systems Simulator Architecture
2017
To avoid any voluntary decisions it is desirable to examine the possible consequences that can be done by simulation. Unfortunately there is no unified methodology and technology for simulators designing. Above mentioned problem when development of each simulator has to be started from the scratches makes elaboration expensive and cumbersome. The article dealt with the way to joint understanding of simulators designing concept.
UV-light induced luminescence processes in Al2O3 bulk and nanosize powders
2010
Abstract UV-light induced photoluminescence (PL) and thermoluminescence (TL) have been studied in the alumina (Al2O3) bulk and nanosize powders. It has been found that luminescence properties of the studied alumina powders are determined mainly by presence of the uncontrolled impurities of titanium, iron and chromium. Despite the general similarity of PL characterized by two main emission band around 400 and 750 nm a number of differences has been observed in relative yield and position of the emission bands as well as in the excitation spectrum of the short wavelength band. Essential differences have been observed also in the intensity of the TL signal, TL curves and TL emission spectra re…
Intrinsic defect related luminescence in ZrO2
2011
The studies of ZrO 2 and yttrium stabilized ZrO 2 nanocrystals luminescence as well as yttrium stabilized single crystal luminescence and induced absorption showed that the intrinsic defects are responsible for luminescence at room temperature. These defects form a quasi-continuum of states in ZrO 2 band gap and are the origin of the luminescence spectrum dependence on the excitation energy. Luminescence centers are oxygen vacancies related but not the vacancies themselves. At room temperature, in ZrO 2 , deep traps for electrons and holes exist. The oxygen vacancies are proposed to be the traps for electrons.
Photoluminescence of Al2O3 nanopowders of different phases
2012
Abstract Photoluminescence was studied in six samples of Al2O3 nanopowders produced from the same initial material by calcination in the 800–1400 °C temperature range. At temperature around 1200 °C phase transition in aluminum oxide lattice occurs; the samples produced at temperatures up to 1200 °C contain mainly δ phase, while those obtained at 1400 °C contain pure α phase. In all studied samples of nominally pure aluminum oxide nanopowders photoluminescence is determined by trace level concentrations of uncontrolled impurities. It was found that phase transition is accompanied with modification of the emission spectrum: a broad band centered around 750 nm presumably ascribed to emission o…
Swift heavy ion induced modifications of luminescence and mechanical properties of polypropylene/ZnO nanocomposites
2014
Abstract The effect of irradiation with 150 MeV Kr ions at fluencies 10 11 and 10 12 ions/cm 2 on luminescence of PP/ZnO nanocomposites and PP matrix has been studied. In unirradiated composite the luminescence is comparatively weak and is contributed mainly by the excitonic luminescence of ZnO. Irradiation of nanocomposite and PP matrix leads to a strong increase of luminescence intensity in a wide spectral range of 360–600 nm. It follows from the obtained results that the enhancement of luminescence originates mainly from the broken bonds in PP matrix. Ion-induced scission of polymer bonds and fragmentation of polymer chains is deduced also from the nanoindentation tests which show a rem…
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.
Photoluminescence and photocatalytic activity of zinc tungstate powders
2011
Abstract ZnWO4 powders with grain size in range 20 nm–10 µm have been synthesized by a simple combustion method and subsequent calcinations. The photocatalytic activities of powders were tested by degradation of methylene blue solution under UV light. The luminescence spectra and luminescence decay kinetics were studied and luminescence decay time dependence on average powder-grain size was obtained. The correlation between self-trapped exciton luminescence decay time and photocatalytic activity of ZnWO4 powders was shown. A model explaining the excitonic luminescence decay time correlation with photocatalytic activity was proposed.
Characteristics of Sintered Materials Obtained from Ferrite Nanopowders Synthesised with Different Methods
2018
Ferrite materials, especially those containing nickel and cobalt, are popular due to their unique mechanical and magnetic properties. Single phase NiFe2O4 and CoFe2O4 nanopowders obtained by different methods were used for sintering studies. Chemical sol-gel self-propagating combustion method, co-precipitation technology combined with hydrothermal synthesis or spray-drying method, and high frequency plasma chemical synthesis have been used to synthesize ferrite nanopowders. Relatively dense (95-99%) materials with high saturation magnetization (MS = 80-84 emu/g for CoFe2O4 and MS = 46-48 emu/g for NiFe2O4) were obtained at 1100-1200 °C temperatures.
Blue luminescence in ZnO single crystals, nanopowders, ceramic
2007
The luminescence spectra and luminescence decay processes were studied in a ZnO single crystal, nanopowders and ceramic at liquid helium and room temperature under VUV synchrotron radiation as well as under pulsed laser excitation. The exciton-exciton and exciton-multiphonon processes were compared in different ZnO nanopowders (commercial powder, powders obtained by vaporization-condensation technique) and ceramic. The possibility of luminescence decay time modification by Al3+ doping was shown.
Photoluminescence in AlN: macro‐size and nano‐powder
2007
Photoluminescence (PL) properties in AlN are studied when size of polycrystalline grains is reduced from macro-size (AlN ceramics and macro-size powder) to nano-size (nano-powder). It was found that in all these materials within the UV- blue spectral region two PL bands are observed at ∼400 nm (caused by the oxygen-related defects) and at 480 nm (with unknown defect structure) but the ratio of their intensities depends on the grain size. Reduction of AlN grain size results in decrease of the 400 nm band and increase of the 480 nm band. It allows the following conclusions: i) reduction of AlN grain size results in decrease of oxygen (the native impurity of AlN) content in the crystalline lat…
Peculiarities of photoluminescence of Al2O3 bulk and nanosize powders at low temperatures
2011
Abstract Photoluminescence has been studied in the aluminum oxide (Al2O3) bulk and nanosize powders in the 300–8 K temperature range. In both samples luminescence spectrum is characterized by presence of broad blue and red bands caused mainly by emission from the uncontrolled titanium impurity. At low temperatures luminescence intensity increases by several times and the red band obtains fine structure. The nature of the fine structure is discussed suggesting manifestation of splitting of the Ti3+ emitting level due to Jahn–Teller effect or overlapping of Ti3+ emission band with narrow lines from other emitting ions. The observed differences in low-temperature spectral features of nanopowde…
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…
Luminescence properties of zirconia nanocrystals prepared by solar physical vapor deposition
2014
Abstract Zirconia nanocrystals have attracted considerable interest as biolabels, which can be used as probes for medical imaging and biosensor applications. However, zirconia particle agglomeration forms a major limitation to its use for biolabeling. In this backdrop, for the first time, well-separated zirconia nanocrystals were obtained in a Heliotron reactor (PROMES CNRS, France) via the solar physical vapor deposition (SPVD) method. As the raw material target for solar evaporation, zirconia nanopowders obtained via the sol–gel process were used. The luminescence and upconversion luminescence properties of the Sol Gel nanopowders were compared with those of the SPVD nanocrystals. Erbium …
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…
Luminescence Properties of ZnO Nanocrystals and Ceramics
2008
The luminescence excitation spectra, luminescence spectra and the nanosecond-scale decay kinetics were studied. The ZnO and ZnO:Al nanopowders were prepared by vaporization-condensation in a solar furnace using different raw powders: commercial, hydrothermal and those obtained by plasma synthesis. Exciton-phonon as well as exciton-exciton interaction processes in nanopowders, a bulk crystal and ZnO ceramics were studied and compared. The fast decay and low afterglow intensity of ZnO nanopowders and ceramics support these materials for scintillators.
The Synthesis, Characterization and Sintering of Nickel and Cobalt Ferrite Nanopowders
2012
The NiFe2O4 and CoFe2O4 ferrites were synthesized by two methods – chemical sol-gel self-combustion method and the high frequency plasma chemical synthesis and magnetic properties, crystallite size, specific surface area of synthesized products are characterized. Nanopowders synthesized in the high frequency plasma are with specific surface area in the range of (28 – 30) m2/g (the average particle size (38 – 40) nm, crystallite size ~40 nm). The ferrite nanopowders obtained by sol-gel self-combustion method have the specific surface area of (37 – 43) m2/g (average particle size (26 – 31) nm, crystallite size (10 – 20) nm). All synthesized nanopowders were sintered via pressure-less sinterin…
Spectral characterization of bulk and nanostructured aluminum nitride
2009
Spectral characteristics including photoluminescence (PL) spectra and its excitation spectra for different AlN materials (AlN ceramics, macro size powder and nanostructured forms such as nanopowder, nanorods and nanotips) were investigated at room temperature. Besides the well known UV-blue (around 400 nm) and red (600 nm) luminescence, the 480 nm band was also observed as an asymmetric long-wavelength shoulder of the UV-blue PL band. This band can be related to the luminescence of some kind of surface defects, probably also including the oxygen-related defects. The mechanisms of recombination luminescence and excitation of the UV-blue luminescence caused by the oxygen-related defects were …
Aging of Nanosized ZnO Modified Polyoxymethylene Blends with Ethylene–octene Copolymer
2015
The influence of ethylene–octene copolymer and zinc oxide (ZnO) on structure and tensile stress–strain behavior of polyoxymethylene were investigated before and after ultraviolet weathering. Addition of ZnO considerably improved stress–strain characteristics of the ultraviolet-irradiation impaired composites. Crystallinities of ultraviolet-irradiated composites were affected by numerous competitive processes, including suppression of crystallization in the presence of multiple components in the system, nucleation induced by nanofiller, secondary crystallization and amorphization because of the chain scissions of the macromolecules. Addition of ZnO considerably improved stability of the comp…
Doped zirconia phase and luminescence dependence on the nature of charge compensation
2017
Financial support provided by the Scientific Research Project for Students and Young Researchers Nr. SJZ2015/25 carried out at the Institute of Solid State Physics of the University of Latvia is greatly acknowledged.
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.
The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia
2014
It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb co-doping were prepared by sol-gel method and thermally annealed to check for the impact of phase transition on luminescence properties. Phase composition and grain sizes were examined by X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison of samples with different oxygen vacancy concentrations and different Nb concentrations confirmed the known assumption that oxygen vacanc…
The luminescence of ZnO ceramics
2010
Abstract The luminescence properties of ZnO ceramics with grains 100–5000 nm sintered by different techniques from nanopowders were studied. The luminescence decay times were compared with that obtained for ZnO single crystal. The temperature dependence of non-exponential decay of defect luminescence (2.0–2.6 eV) was measured in wide time, intensity and temperature range. The luminescence decay kinetic at T ≤ 20 K shows the decay close to I(t) ∼ t−1 dependence. At temperature region 50–250 K the decay kinetics is more complicate since the TSL was observed in this temperature region. It is shown that the luminescence properties of NP and ceramics strongly depend on defect distribution on gra…
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 .
Synthesis of Eu<sup>2+</sup> and Dy<sup>3+</sup> Doped Strontium Aluminates and their Properties
2016
Strontium aluminate phosphors were synthesized by the solution combustion method using citric acid, urea or glycine as reducing agent and europium and dysprosium as dopants. The content of both dopants was in the range of 1 – 2 mol%. Dependence of phase composition, crystallite size and specific surface area on calcinations temperature, used reducing agents and dopants were determined. Luminescent properties of the calcinated at 1300 °C powders contained SrAl2O4 (90 %) and Sr4Al24O25 (10%) phases with crystallite size of 80 nm were determined.