Search

Transients in a high- and medium-voltage power-supply network due to switching operations and short circuits are accompanied by high-frequency overvoltage pulses. Their amplitude and frequency characteristics are needed to select proper protection devices. Only experimental study can give us reliable data on such characteristics. The paper presents overvoltage spikes experimental study data in switchgears of 6–500 kV. The spikes were measured by means of recorder with noncontact capacitive sensors. Experimental studies at power-engineering facilities showed that most hazardous phenomena are high-frequency resonances. In this case, the overvoltage values are over ten times higher than nominal voltage amplitude. The usual method of connecting protection device to mains via a conductor a few meters long was shown to be inadequate to provide equipment protection. RC circuits are needed for this situation.

A technique for forming Au/SiO2 core/shell nanoparticles is developed. A long-wavelength shift of the extinction spectrum peak from 520 nm to 538 nm with increasing SiO2 shell thickness from a monolayer to 10 nm is established. It is experimentally shown that the anomalous spectral shift of the extinction spectrum peak of Au/SiO2 nanoparticle arrays from 538 nm to 720 nm, observed with increasing the SiO2 shell thickness, is caused by the formation of Au nanoparticle di- and trimers within one SiO2 shell. This effect is theoretically explained for the case of Au nanoparticle dimers.

The effect of laser radiation with a wavelength near 1.55 µm on the photoluminescence properties of “nitrogen-vacancy” (NV) color centers in diamond has been studied experimentally. The effect of radiation of an infrared laser on the charge state of color centers redistributes the spectral intensity of photoluminescence in the ensemble of NV centers. In the case of neutral NV centers, the quenching of photoluminescence reaching about 60% has been observed. A feature of the laser excitation of NV centers by this method is the absence of competition with stimulated emission and two-photon excitation, which is observed with an increase in the power of infrared radiation at other wavelengths.

The contact surfaces of the banding shelves of adjacent steam turbine blades made of titanium VT6 alloy after operation are studied by fractography, micro-X-ray and microstructural analysis and determination of mechanical properties. The different types of destruction of the contact surfaces are analyzed and explained. It is shown that the reason for intensive abrasion of the turbine blades' binding meshes is violation of the welding mode in the station conditions.

We report the results of systematic experimental and theoretical studies of structural and dynamical properties of short-period GaN/AlN superlattices. The multilayer structures with the thicknesses of the constituent layers varying from two to several monolayers are grown using the submonolayer digital molecular beam epitaxy technique. In the framework of density functional theory, the lattice dynamics properties of the superlattices are studied. Good agreement between the experiment and theory is found, which made it possible to establish unambiguously a relationship between the features observed in the Raman spectra and the microscopic nature of the acoustic and optical phonon modes. The results obtained enhance the capabilities of Raman spectroscopy as a fast and non-destructive characterization method of short-period GaN/AlN superlattices and can be used to optimize growth process parameters for the fabrication of structurally perfect low-dimensional heterostructures.

The luminescence properties of colloidal Ag2S quantum dots (QDs) with ZnS or SiO2 shells coated with thioglycolic or 2-mercaptopropionic acids are comparatively analyzed. It is demonstrated that the quantum yield of the IR recombination luminescence of colloidal Ag2S QDs increases by a factor of up to 35 as a result of formation of ZnS or SiO2 shells with a simultaneous increase in the average luminescence lifetime. It is shown that the radiative and nonradiative recombination constants for core/shell Ag2S/ZnS QDs coated with thioglycolic acid decrease, which is explained by localization of electrons in the shell and localization of holes in the core. In core/shell Ag2S/SiO2 QDs coated with 2-mercaptopropionic acid, the radiative recombination constant increases and the nonradiative recombination constant decreases. In this case, the increase in the radiative recombination constant is caused by localization of electrons and holes in the core. The decrease in the nonradiative recombination constant is explained by passivation of interface defects of QDs upon the shell formation.

The main contribution to the luminescence of LiNbO3 : Zn (0,04 ÷ 2,01 mol. %) at 420 and 440 nm was established to be due to two electro-hole pairs of Nb4+–O-in niobium octahedron. Moreover, the luminescence weakly depends on Li / Nb ratio and Zn concentration. The increase of Zn concentration to 2,01 mol. % ZnO leads to monotonically increasing intensity in long-wave region of the photoluminescent spectra. This fact indicates that there are shallow energy levels near bottom of the conductivity band. Also the features of hydrogen bonds in LiNbO3structure effects on the location of the shallow energy levels as the complex defects caused by OH-group in the structure can contribute to the photoluminescence.

The photoluminescence intensity in lithium niobate crystals close to the stoichiometric composition being lower than in a congruent crystal was established. The increase of Li / Nb ratio leads to shifting the photoluminescence bands to the short-wavelength region of the spectrum and changing the fundamental absorption edge of the crystals under study. It was shown that, in addition to point defects in the cationic sublattice, complex defects due to the presence of OH groups and compensation defects (VLi / VNb) in the structure can also contribute to photoluminescence.

We consider the manufacturing process of forgings for turbine blades of extra-large dimensions (length >2 m) from electroslag remelting steel 15H11MF-Sh. With an increase of the workpiece dimensions (weight >450 kg), we face the problem of choosing the technology for obtaining the original billet. The production technology is known to affect the structure of the material and, as a consequence, the final properties of the product. We present the results of studying the influence of the method of obtaining the original metal blanks (hot-rolled steel bars and forged billets) on the properties of large-sized forgings of turbine blades. The mechanical characteristics, microstructure properties, chemical composition and content of δ -ferrite were determined by examining the initial samples of long products and forged rods. It is shown that billet in the forged state exhibit higher strength characteristics. However, after the stamping process, the properties of the blades equalize, i.e., after stamping and heat treatment, the same structure is formed, regardless of the method of obtaining the original workpiece. The results obtained can be used in the serial production of large-sized turbine blades of a new profile.

We analyze the features of nonlinear refraction in colloidal solutions containing Ag2S quantum dots capped with thioglycolic acid (Ag2S/TGA) or L-cysteine (Ag2S/L-Cys), with the quantum-dot (QD) sizes ranging from 1.7 to 5.5 nm and their concentration in the solution being 0.1%. The Z-scans of the samples were obtained using 10 ns pulses of 532 nm radiation. For samples with various average sizes and positions of the characteristic feature in the optical density spectrum, both self-focusing and self-defocusing of radiation were observed. The contribution of thermal refraction to the recorded Z-scans was estimated, and the impact of thermal effects on the observed nonlinear refraction was shown to be negligible. The solutions of the Ag2S/TGA QDs with the ground state exciton absorption peaked at 590 nm exhibit self-focusing. The samples with recombination luminescence and the ground state exciton absorption peaked at 750 nm reveal self-defocusing. We show that nonlinear refraction in the case of nanosecond pulses is predominantly nonthermal in nature and is due to absorption by free charge carriers, as well as due to the band filling effect in the Ag2S QDs, which involves localized states of impurities.

In this work, manifestations of IR luminescence sensitization of Indocyanine Green during conjugation with colloidal Ag2S quantum dots with an average size of 2.2 and 3.7 nm, passivated with thioglycolic acid molecules (Ag2S/TGA QDs) are studied using absorption and luminescence techniques. The possibility of enhancing luminescence in the dye monomer band (820 nm) under excitation at 660 nm by a factor of 6 in the presence of Ag2S/TGA QDs (2.2 nm) due to a decrease in the polymethine dye chain movement via coordination interaction with QDs was demonstrated. The way to switch-over from the first therapeutic window of biological tissue transparency (NIR-I, 700–950 nm) to the second (NIR-II, 1000–1700 nm), based on sensitization of IR luminescence of Ag2S/TGA QDs with an average size of 3.7 nm in the region of 1040 nm due to of resonance non-radiative transfer of excitation energy from Ag2S/TGA (2.2 nm) QDs at 900 nm to Ag2S/TGA QDs (3.7 nm) via the J-aggregate of ICG dye, which acts as an exciton bridge.

A LiNbO3:Zn (4.69 mol % ZnO) crystal grown from a charge synthesized using homogeneously doped Nb2O5 as a precursor has been shown to contain less luminescence centers in comparison with a LiNbO3:Zn (4.60 mol % ZnO) crystal prepared via direct doping. In the case of LiNbO3:Zn crystals prepared via direct doping, the intensity of all luminescence bands varies monotonically as the ZnO concentration is raised to 4.60 mol %. At a ZnO concentration of ~4.60 mol %, the intensity of all the bands changes sharply, suggesting that the system of luminescence centers in the material undergoes structural changes.

Bulk photoluminescence of congruent and near-stoichiometric lithium niobate crystals that were obtained by different technologies is studied. It is found that the luminescence intensity in crystals whose composition is close to stoichiometric is lower than that in congruent crystals. It is shown that not only luminescence centers of the main types, which are caused by the occurrence of NbLi, VLi, etc., point defects, but also complex defects that are caused by the occurrence of OH groups in the structure can contribute to luminescence.

Volume and surface photoluminescence of congruent and stoichiometric lithium niobate crystals obtained using various technologies was studied. The luminescence intensity of the stoichiometric crystal was less than that of the congruent one. Volume luminescence of the crystals was mainly caused by NbLi defects while luminescence quenching of the near-surface layer was observed in the long-wavelength spectral region (>500 nm) because of energy scattering in crystal-lattice vibrations and increased luminescence intensity of the $$ {\mathrm{Nb}}_{\mathrm{Nb}}^{4+}-{\mathrm{O}}^{-} $$ pair. Luminescence bands with maxima at 426 and 446 nm were caused by complex defects in the form of electron–hole pairs $$ {\mathrm{Nb}}_{\mathrm{Nb}}^{4+}-{\mathrm{O}}^{-} $$ in which the Nb atom was bound to oxygen atoms by covalent and ionic bonds. An increase of the Li/Nb ratio led to a shift of the luminescence bands to shorter wavelengths and a change of the fundamental absorption edge of the studied crystals.

The possibility to obtain novel data by standard electron spectroscopy and quantum chemical techniques is exemplified by C2FBr0.15 intercalate and silver foil. The features of extended X-ray photoelectron spectra are interpreted by electronic transitions in the valence band of similar unit cells. The analysis of experimental and calculated spectra reveals two states of intercalated Br2: molecular and chain-like. The interaction of Ag with NO2 at 300–520 K is limited by the formation of an oxidized state in the near-surface layer with a thickness of ∼6 A, with the metallic state of silver dominating in the Ag3d И Ag MNN spectra. Geometric parameters, states of atoms, and the character of bonds between them are consistent with the previously obtained results.

GdNbхTa1 –хO4 and YNbхTa1 –хO4 (x = 0–1) ceramic samples have been prepared by a sol–gel process, and the luminescence properties of the solid solutions have been studied under UV excitation. The results demonstrate that even a relatively small amount of tantalum (x = 0.9) in GdNbхTa1 –хO4 leads to a sharp increase in the luminescence intensity related to Nb4+–O– centers, which exceeds the luminescence intensity in the GdNbO4 and GdTaO4 individual compounds by a factor of 3–6.5. The luminescence signal in the YNbхTa1 –хO4 solid solutions exceeds that in the YNbO4 and YTaO4 end-members at any Nb : Ta ratio, owing to energy transfer between Nb4+–O– and Ta4+–O– emission centers.

The paper presents an improved methodology for determining the reduction in sections of cold-formed thin-walled profiles, which allows simplifying and automating the calculation process for specific sections. This approach implies the necessity to specify only the initial data, and the entire calculation process takes place in the automated mode, which can significantly reduce its complexity.

There has been carried out an improvement of the methodology for determination of reduced sections with the simultaneous action of the entire complex of efforts (including bimoment ones).The solution presented in dimensionless parameters uses the «Section» algorithm and the EUROCODE provisions regarding section reduction. At the beginning, a general dimensionless parameter of efforts is determined, which corresponds to the limiting conditions for ensuring the local stability and section shape. Then, as the specified parameter grows further, the development of the section reduction to the limiting state is considered. As this takes place, the reduced sections are replaced with unreduced ones with loading with fictitious forces that compensate for the reduction. The authors propose a high-speed method for determining the local stability loss coefficients and the cross-sectional shape in dimensionless parameters, which allows obtaining more reliable results of strength control in comparison with those included in the current regulatory literature. The method is illustrated using calculation examples with comparison of the EUROCODE results, which have shown quite significant discrepancies.

Expressions are obtained for the IMVV/I3d ratio of the AgMVV Auger line intensity to the Ag3d photoemission line intensity in XPS spectra (AlKα radiation, hν = 1486.6 eV) of Au-Ag bimetallic particles located on the flat surface of the support. Bimetallic hemispherical particles with non-uniform distribution of metals (silver core covered with a gold shell) are considered. The particles are characterized by normal size distribution (with respect to the core radius R) with a maximum at Rmax = 3.5 nm and the standard deviation σ = 0.5 nm, 1.0 nm, and 2.0 nm. The bimetallic system is analyzed in the conditions of R-independence: in one case, the shell thickness δ = const(R); in the other case, the atomic ratio of gold to silver γ = const(R). As the Au-shell is formed around the Ag-core and y increases, the IMVV/I3d ratio is shown to decrease significantly due to more effective screening by the shell of AgMVV Auger electrons as compared to that of Ag3d photoelectrons. The IMVV/I3d ratio as a function of γ weakly depends on σ and on the choice of conditions δ = const(R) or γ = const(R). When an alloy with a uniform spatial distribution of gold and silver atoms over the particle volume is formed, the IMVV/I3d ratio also decreases with increasing γ, though to a much smaller extent. The derived expressions can be used in XPS studies to consider the formation of supported bimetallic particles in model planar systems and the changes occurring with the particles as a result of heat-treatment in the reaction medium.

Behavior of gold films supported on the surface of a silver foil is studied using X-ray photoelectron spectroscopy (XPS) when heated in a vacuum or in nitrogen dioxide (under pressure of 10−5 mbar) at 200 °C. The initial gold film is 2–2.7 nm thick. It is shown that the gold film dissolves in the silver foil volume during the heating to form an Ag–Au alloy. The behavior of the ratio of the AgMVV Auger line intensity to the Ag3d photoemission line intensity testifies that the alloy surface is enriched with silver. The enrichment proceeds more efficiently when the system is heated in the presence of NO2.

We report the results of systematic Raman spectroscopy studies of AlxGa1 –xN (x ~ 0.75) layers grown using plasma-assisted molecular beam epitaxy at various stoichiometric conditions and growth fluxes. The high-intensity asymmetric low-frequency peak obeying Bose statistics is discovered in Raman spectra of the layers grown by temperature-modulated epitaxy at strongly Ga-enriched conditions. Theoretical model is developed to explain the origin and the high intensity of the observed low-frequency peak, which is attributed to the presence of excessive metallic gallium in AlGaN layers and can be explained by vibrations of gallium clusters with a diameter of ~1 nm. The nature of the low-frequency peak is similar to that of the boson peak in glasses, which occupies the same frequency range in Raman spectra. We demonstrate the capabilities of Raman spectroscopy as an express and non-destructive technique for optimization of growth conditions of AlGaN layers to achieve simultaneously the atomically-smooth droplet-free surface morphology and the high structural quality.

Features of nonlinear refraction formation in colloidal solutions containing Ag2S quantum dots passivated with thioglycolic acid (Ag2S/TGA QDs) with a concentration of 0.1% and an average size of 2.0 nm are considered. Nonthermal self-focusing caused by the “band filling” effect under exciton excitation was detected by the Z-scanning method for 10-ns pulses of a YAG:Nd laser at a wavelength of 532 nm for Ag2S/TGA QDs having an exciton absorption maximum at 590 nm.

The effect of alloying on the properties of highly tempered steels used for production of a range of petroleum pipes is studied. It is shown that an increase in molybdenum content from 0.15 to 0.53% improves the mechanical characteristics of chromium-molybdenum steels tempered at 600–690°C significantly. Alloying with vanadium and niobium facilitates an additional increase in strength properties. The best hardening of steel with 0.32% molybdenum in a highly tempered condition is provided by combined microalloying with niobium and vanadium, although stress corrosion cracking resistance is reduced.

The relationship of the spectral luminescent and nonlinear optical properties of Ag2S quantum dots (QDs), passivated with thioglycolic acid (Ag2S QDs/TGA) and Ag2S QDs, stabilized by gelatin (Ag2S QDs/Gel) with average sizes from 1.5 nm to 2.1 nm is found. Colloidal Ag2S QDs/TGA with different sizes, having the exciton (620 nm) and recombination (660 nm, 880 nm and 1205 nm) luminescence were studied using the methods of luminescent spectroscopy, luminescence decay, and Z-scans technique at the wavelengths of 532 nm using 10 ns pulses. Resonant two-photon transitions of reverse saturated absorption (RSA) were found for samples with recombination luminescence. In addition, the nonlinear refraction of thermal nature was observed using Z-scan method. Predominantly weak two-photon absorption (TPA) and nonlinear refraction (NR) of non-thermal nature occur for Ag2S/TGA quantum dots with exciton luminescence. The luminescence lifetimes support this conclusion. The differences in luminescence lifetimes of samples are associated with different state of interfaces for colloidal Ag2S QDs/TGA with recombination and exciton luminescence. This conclusion was confirmed by FTIR spectroscopy of colloidal Ag2S QDs/TGA solutions, synthesized under different conditions. RSA is characteristic of samples with a noticeable concentration of trap states acting as recombination luminescence centers (660 nm). The maximum effect was noted for Ag2S QDs with recombination luminescence in the region of 660 nm, 880 nm, 1205 nm. The fast component of this luminescence decay has a time constant of about 0.8 ns. It decay 5 times for the first 10 ns. In the case of Ag2S QDs/TGA with exciton luminescence (620 nm) there are no appropriate conditions for RSA. The fast component of luminescence decay has a time constant of 0.8 ns. The luminescence intensity decreases 50 times for the first 10 ns. In this case, TPA and nonlinear refraction of non-thermal nature take place, and RSA is absent.

Regularities of reverse photodegradation of infrared (IR) luminescence of colloidal Ag2S quantum dots (QDs), stabilized in gelatin with the average size of 1.6 nm ( λ lum max = 1205 nm) and passivated with thyoglicolic acid with the average size of 2.3 nm ( λ lum max = 1095 nm) were discussed. The photochemical nature of this process was found. The evidences of the formation of nonradiative recombination centers near the IR luminescence centers was found. These centers disintegrate in the dark with the activation energy of 0.9 eV and ensure the recovery of intensity IR luminescence of Ag2S QDs by 65–75%.

We present the results of the study of the nonlinear optical response observed in hybrid associates of Azure A dye with Zn0.5Cd0.5S colloidal quantum dots upon exposure to 10-ns pulses of the second harmonic (532 nm) of a Nd3+:YAG laser. It is shown that association enhances the absorption saturation in the dye by a factor of 4.5, which is caused by charge phototransfer between the components of the hybrid associate.

We have considered the resonant nonradiative energy transfer in hybrid associates of thionine dye (TH+) molecules and Ag2S colloidal quantum dots (QDs) passivated with thioglycolic acid (Ag2S/TGA) and Ag2S QDs stabilized with gelatin (Ag2S/Gel). Used samples of Ag2S QDs possess luminescence, which arises by the exciton mechanism, as well as by the recombination mechanisms of holes with electrons localized at luminescence centers and of electrons with holes localized at the luminescence centers. The quenching of luminescence of Ag2S/TGA QDs (1.8 nm) with a maximum at 630 nm and a decrease in the luminescence lifetime from 13.7 to 6.5 ns, which occurs upon association with TH+ molecules, have been established. On the contrary, for associates of Ag2S/TGA QDs (5.5 nm) with TH+ molecules, we have observed the quenching of luminescence of the dye and a decrease in the lifetime of this luminescence from 0.43 to 0.3 ns, as well as an enhancement of luminescence of QDs. In the case of hybrid association with TH+ molecules, the luminescence enhancement of Ag2S/Gel QDs (1.6 nm) has been established, which results from the recombination of free holes with electrons localized at luminescence centers. Based on our analysis of the luminescence kinetics of the dye, we have inferred the occurrence of resonant nonradiative energy transfer from TH+ molecules to centers of recombination luminescence in Ag2S/TGA (5.5 nm) and in Ag2S/Gel (1.6 nm) QDs with its maxima at 950 and 1205 nm, respectively. For Ag2S/TGA QDs (2.2 nm), which luminesce with a maximum at 620 nm by the exciton mechanism, we have observed a significant overlap both between the luminescence spectra of QDs and TH+ and between their absorption spectra. Close parameters of the luminescence kinetics for both the initial components and their associates indicate the energy transfer, which is realized in opposite directions.

X-ray photoelectron spectroscopy is applied to study at room temperature and pressure of 10–5 Torr the interaction of NO2 with a model sample obtained by thermal deposition of silver on the graphite surface. Scanning tunneling microscopy shows that in this case, silver particles with a size of D = 4–11 nm are formed on the surface. For comparison, polycrystalline silver foil is studied under similar conditions. It is found that such a treatment leads to silver oxidation in the Ag/C sample while the foil remains unchanged under these conditions.

Expressions are obtained for the intensities of photoemission lines of silver and gold in bimetallic particles formed during sequential deposition of metals on the flat surface of the support. Two cases are considered: bimetallic particles with a non-uniform distribution of metals (silver core covered with a gold shell) and alloy particles of uniform composition. The particle shapes are assumed to be hemispherical. Expressions were obtained for the photoemission lines of gold Au4f, Au3d3/2 and silver Ag3d as well as for the Auger line of silver AgMVV recorded using radiation AlKα (hν = 1486.6 eV) and AgLα (hν = 2983.4 eV). Gold shells on the surface of silver particles are shown to diminish the intensity ratio of AgMVV line to Ag3d line, and this effect becomes stronger with the increasing ratio γ of gold atoms to silver atoms. In the case of alloy particles Ag–Au, the intensity ratio of these lines also decreases with increasing γ, though to a much lesser extent. The intensity ratios of gold Au4f and Au3d3/2 lines to the silver Ag3d line are also considered. The obtained equations can be used in XPS studies to consider formation of bimetallic particles in model planar systems and the changes occurring with the particles as a result of heat treatment in a vacuum or in a reaction medium.

We study the features of the nonlinear optical response of silver nanoparticles (Ag NPs) of the spherical and triangular shapes synthesized using a citrate-borohydride approach. The Z-scans were used to analyze the nonlinear optical absorption of Ag NPs of different morphology, particularly, the concurrence of saturable and reverse saturable absorption in the solution containing triangular Ag NP. We show the significant contribution to the increase in the normalized transmittance accomplished by photochemical degradation of the non-spherical Ag NPs (extinction maximum of 600 nm) and transformation into the spherical ones (extinction maximum of 400 nm). The nonlinear light scattering is analyzed as well, which showed the contribution to the variation of the sample transmission when it approaches the focal plane.

The paper presents the results of a study of shallow non-radiative trap states in colloidal Ag2S QDs and Ag2S/SiO2 core/shell QDs, passivated with 2-mercaptopropionic acid in ethylene glycol carried out the thermally stimulated luminescence technique. For Ag2S QDs, the presence of thermoluminescence peaks in the region of 150–330 K was established. The formation of the SiO2 shells leads to the disappearance of the thermoluminescence peak at 250 K. It is interpreted as a “healing” of defects, localized on Ag2S QD surface. The depths of the detected trap states were estimated using a kinetic model. They showed that the observed thermoluminescence bands are due to the presence of shallow holes trap states in Ag2S QDs with depths of 0.117 eV and 0.135 eV for the thermoluminescence peaks at 190 K and 250 K, respectively.

High-pulse repetition rate lasers allow significant enhancement in the average power of the low-order harmonics generation in isotropic media. We report on the third (343-nm) and fifth (206-nm) harmonics generating in air and different nanoparticle-containing laser-produced plasmas by applying Yb-doped fiber laser delivering 37-fs, 100-kHz, 1030-nm, 0.5-mJ pulses. Different characteristics of these processes (power and density dependences, influence of impeding processes, role of synthesized nanoparticles, variations of the spectral modulation of driving pulses, etc.) are analyzed. We compare the formation of the plasmas on the surfaces of aluminum, carbon, manganese, and titanium bulk species, as well as quantum dots of metal sulfides as the media for low-order harmonics generation, using 250-fs (1030-nm) and 5-ns (1064-nm) heating pulses at different delays between the heating and driving pulses. Average power of about 20 mW was estimated for the third harmonic emission from metal plasmas, with 3 × 1016 UV photons (343 nm) emitted per second.

The natural deep eutectic solvent (NADES) based on choline chloride (ChCl) and lactic acid (LA) was used for the preparation of chitosan (CS) films by the solution casting method. The content of NADES in films was from 0 to 82 wt%. The impact of NADES on the morphology and crystalline structure of films was investigated using scanning electron microscopy as well as wide-angle and small-angle X-ray scattering. The experimental results allow to propose CS chains swelling in NADES. FTIR spectroscopy confirms the interactions between CS and NADES components via the formation of hydrogen and ion bonds. The thermal properties of the composite films were studied by simultaneous thermogravimetric and differential thermal analysis. Thermomechanical analysis demonstrated appearance of two transitions at temperatures between &minus, 23 and &minus, 5 &deg, C and 54&ndash, 102 &deg, C depending on NADES content. It was found that electrical conductivity of film with 82 wt% of NADES reaches 1.7 mS/cm. The influence of the composition and structure of films on the charge carriers concentration and their mobility is discussed.

In this work the relaxation processes of chromophores containing copolymers are considered. These processes were studied using the method of thermostimulated depolarization technique. Thermograms for linear and branched azo-chromophore containing methacrylic copolymers were obtained and explained. A comparison of the obtained results demonstrates an increase in the activation energy of relaxation processes for branched copolymers.

The analysis of nonlinear optical properties of thiazine dye molecules of Methylene Blue (MB+), located in the near-field zone of spherical gold nanoparticles, coated with a silicon dioxide shell (Au/SiO2 NPs) has been performed. The increase in the reverse saturated absorption, characteristic of MB+ dye in the presence of gold nanoparticles under the 532 nm YAG:Nd3+ laser second-harmonic pulses (10 ns) was found using Z-scan technique. The mechanisms of the plasmon nanoparticles effect on optical transitions, determining the reverse saturated absorption in methylene blue monomers are discussed. It is concluded that an increase in the effective cross section for triplet-triplet absorption of MB+ molecules in the presence of Au/SiO2 NPs makes the greatest contribution to the observed effect.

In this work, we investigated the nonlinear optical response of ensembles of gold nanorods (Au NR) with an average size of 6×18 nm dissolved in water, passivated with cetyltrimethylammonium bromide (CTAB). Negative nonlinear refraction with an index γ = –3.5·10-15·cm2·W-1 and nonlinear absorption were found using Z-scan technique in a field of the second harmonic of 10 ns YAG:Nd3+ laser pulses with a wavelength of 532 nm. The Z-scan profile demonstrates the samples bleaching as well as an increase in absorption near the lens focal plane in the case the pulse energy increases to 0.16 mJ. It was shown that the sample bleaching is caused by a decrease of optical density at a wavelength of 532 nm as a result of the photoinduced transformation of nanoparticles from cylindrical to a spherical shape passing through the melting stage.

International audience; Electronic structure of series of tellurium oxide crystals within the TeO 2-TeO 3 binary system is studied with generalized gradient approximation to DFT, hybrid DFT-HF method with the PBE0 and B3LYP exchange-correlation functionals and with quasiparticle G 0 W 0 approach. Comparison with available experimental data revealed significant underestimation of the band gap values within DFT. The hybrid DFT-HF method leads to slightly overestimated values of the bandgap, and the best agreement with experimental data provides the "one-shot" G 0 W 0 calculations starting from Kohn-Sham solutions. The electronic structure of tellurium oxides is discussed in details. It is found that bandgap value decreases proportionally to fraction of tellurium atoms in octahedral coordination. This change is due to formation of gap states by 5s(Te) electrons which do not participate in Te(VI)-O bonding. Dielectric properties is calculated within Random Phase approximation for the series of tellurium oxides and high nonlinear properties of the compounds is predicted by empirical Miller's rule.

The results of studies of the optical properties of ensembles of colloidal CdS quantum dots passivated by thioglycolic acid are reported. The average dimensions of the quantum dots lie in the range from 1.7 to 5.8 nm. By X-ray diffraction studies and Raman spectroscopy, it is established that quantum dots crystallize with the formation of a cubic crystal lattice. The systematic features of the quantum-confinement effect in the optical absorption and luminescence spectra, as well as in the luminescence excitation spectra, are established. The features manifest themselves as a blue shift of the corresponding bands with decreasing quantum-dot dimensions. From analysis of the nanosecond luminescence kinetics, it is concluded that experimentally observed radiative recombination proceeds by the donor–acceptor mechanism.

The luminescent properties of hybrid nanostructures constructed from colloidal quantum dots (QDs) of CdS passivated with thioglycolic acid, europium(III) tris(tenoyltrifluoroacetonate), and methylene blue dye molecules are studied. Spectral features typical for the formation of core/shell QDs of the CdS/CdS:Eu3+ type are found. It is noted that the adsorption of the europium complex at the QD interfaces and the formation of QDs of the CdS/TGA/Eu3+ are probable. Spectral patterns that reveal nonradiative energy transfer from the recombination luminescence centers of CdS QDs to the Eu3+ ions in the CdS/CdS:Eu3+ and CdS/TGA/Eu3+ structures are obtained. This is manifested in quenching the recombination luminescence of QDs and in the ignition of the intracentric luminescence of Eu3+, which enhance with an increase in the concentration of the europium complex. When such structures are combined with methylene blue molecules, the half-width of the absorption spectra is found to increase by 10–15% with an unchanged position of the absorption band maximum. With an increase in the concentration of methylene blue molecules, decreases in the intensity of the recombination luminescence band of CdS QDs at a wavelength of 530 nm and in the luminescence intensity of Eu3+ ions and simultaneously the rise up of the fluorescence of methylene blue at a wavelength of about 675 nm are observed. At the same time, a decrease in the luminescence lifetime of the bands of QDs and europium ions are observed. It is concluded that the nonradiative excitation energy transfer from both the recombination luminescence centers and Eu3+ ions to methylene blue molecules takes place.

Luminescence studies of singlet-oxygen photosensitization by methylene blue molecules in various solvents, as well as by hybrid associates of this dye with colloidal Ag2S quantum dots with average sizes of 2.0, 2.4, and 2.7 nm, are performed. The conditions for simultaneous singlet-oxygen photosensitization and detection of the IR luminescence of colloidal Ag2S quantum dots passivated by thioglycolic acid are determined.

Temperature properties of recombination IR luminescence (1240 nm) for ensembles of colloidal Ag2S quantum dots with an average size of 3.6 ± 0.5 nm have been investigated in gelatin. Thermostimulated luminescence, resulting from varying temperatures and at continuous photoexcitation of colloidal Ag2S quantum dots, has been detected. A peak of thermolumination has been found at the temperature region of 100–240 K, which is maintained by two components, the presence of which is by the existence of two types of hole trap states with depths of 0.07 and 0.09 eV.

The nonlinear-optical (NLO) activities of composite materials with a binary set of chromophores are measured with the Second Harmonic Generation technique (λ=1064 nm). In these materials the host matrix is an epoxy amine polymer with an azochromophore, covalently attached in such a way that its donor-group is included in the main chain. Apart from this chromophore functionalized epoxy amine oligomer, CFAO, a guest azochromophore dispersed orange, DO3, is added. The addition of DO3 in two concentrations (10 and 20 wt%) enhances the NLO coefficient compared to that for CFAO by ca. 40%. Molecular modeling in an amorphous cell is used for estimating the local mobility of different groups and fragments of the polymeric chain, in particular, that of the azochromophores. The information obtained from the modeling can be used for the development of an effective time-temperature poling protocol. It is shown that for a high chromophores orientation the poling temperature should be some 20–30 K higher than the glass transition Tg.

The solution of the problem of investigating the energy structure of trap states and photophysical processes with their participation is necessary for the effective application of colloidal Ag2S quantum dots. These studies are important both for finding ways to increase the quantum yield of luminescence, and for the effective using of non-luminescent trap states in photocatalysis applications. In this paper, Ag2S quantum dots prepared with an aqueous synthesis in a gelatin matrix were investigated. The investigated Ag2S quantum dots have average sizes of 2.2 ± 0.3 nm, 2.5 ± 0.5 nm and 3.6 ± 0.5 nm, according to TEM data, and size-dependent spectra of UV–Vis absorption and photoluminescence. Temperature dependencies of IR recombination luminescence (1200–1250 nm) for ensembles of colloidal Ag2S quantum dots, dispersed in gelatin, were investigated. Thermostimulated luminescence, appearing under the variation of temperature and continuous photoexcitation of colloidal Ag2S quantum dots, was detected. The peak of thermoluminescence was found in the temperature region of 120–240 K, which consists of two components. Energies of activation of thermoluminescence and temperature quenching of IR luminescence were determined. The activation energy is in the region of 0.05–0.11 eV. And the energy of temperature quenching of IR luminescence is at 0.06–0.10 eV.

The results of studying degradation of the optical properties of colloidal Ag2S and CdS quantum dots (QDs) 2.6–3.2 nm in size passivated by thioglycolic acid (TGA) are presented. The photoluminescence intensity of colloidal Ag2S QDs has been found to decrease under laser irradiation at a wavelength of 445 nm, beginning with the effective power of 10 mW. The observed effect is interpreted as a photochemical reaction of formation of new nonradiative-recombination channels in Ag2S QDs upon excitation. It is established for colloidal CdS QDs passivated by TGA that a decrease in the optical density in the entire absorption spectrum and the luminescence intensity is accompanied by precipitation of the colloidal particles in a cell and related to photodegradation of the passivating shell.

Approaches are developed for controlling the size effect in the absorption and photoluminescence properties of colloidal CdS and Zn0.5Cd0.5S quantum dots (QDs) in a gelatin matrix and thioglycolic acid. We analyze spectroscopic manifestations of dark Ostwald ripening and size-selective photoetching and demonstrate that the illumination of molten colloidal CdS and Zn0.5Cd0.5S QD solutions at a wavelength lying at the optical absorption edge in the presence of hydrogen peroxide as a catalyst for photoetching leads to a blue shift of the optical absorption and photoluminescence spectra of the QDs. Analysis of TEM images of QD samples leads us to conclude that photoetching reduces the average QD size as a consequence of the photodissolution of the CdS and Zn0.5Cd0.5S compounds. We demonstrate that, by contrast, heat treatment of the synthesized CdS and Zn0.5Cd0.5S QD sols at a temperature between 75 and 90°C leads to an increase in nanocrystal size through recrystallization, which shows up as a redshift of the optical absorption and photoluminescence spectra of the corresponding samples.

Spectral, kinetic, and nonlinear optical regularities that demonstrate the exchange of electronic excitations between the components of hybrid associates of Ag2S colloid quantum dots (1.7–1.8 nm) in gelatin with molecules of thiazine dyes (Ds) are found. When the IR luminescence of Ag2S quantum dots (QDs) is excited by radiation from the thionine absorption region, its enhancement due to nonradiative resonant energy transfer is observed. The association with methylene-blue molecules blocked the IR luminescence of Ag2S QDs upon its excitation by radiation from the absorption region of the dye due to the transfer of charge carriers. It is demonstrated that the hybrid association of thionine molecules and Ag2S QDs adversely affects the nonlinear optical properties of the latter, which manifests itself in inverse saturated absorption by the action of 10-ns second-harmonic pulses (532 nm) of a Nd3+:YAG laser. For the associates of Ag2S QDs with methylene-blue molecules, the radiation focusing caused by the transfer of charge carriers from the dye and the change in the population of small traps in nanocrystals is found. It is concluded that the direction of the transfer of electronic excitations and the photophysical processes in these objects are determined by the mutual arrangement of the HOMO–LUMO levels of the dye with respect to the levels of dimensional quantization of the Ag2S QDs.

Strain aging of pipe steels 06G2FB and 07G2MFB with ferrite-pearlite and ferrite-bainite structures is investigated. It is established that a ferrite-bainite structure is more inclined towards strain aging than a ferrite-pearlite structure. The tendency towards strain aging of steel with a ferrite-bainite structure increases with increasing austenitizing temperature. During hot plastic deformation there is development of recrystallization and the tendency towards strain aging decreases.

The effect of high-temperature thermomechanical treatment (HTMT) on the brittleness connected with deformation-induced aging and on the reversible temper brittleness of a low-carbon tube steel with a ferrite–bainite structure has been studied. When conducting an HTMT of a low-alloy steel, changes should be taken into account in the amount of ferrite in its structure and relationships between the volume fractions of the lath and the acicular bainite. It has been established that steel subjected to HTMT undergoes transcrystalline embrittlement upon deformation aging. At the same time, HTMT, which suppresses intercrystalline fracture, leads to a weakening of the development of reversible temper brittleness.