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Methods of synthesis of nanotubular structures based on titania of various phase and chemical compositions are described. A systematic account is given of known data about the influence of synthesis and subsequent treatment conditions on the amorphous and crystal structures, specific surface area, morphology and optical, luminescence and electro-physical properties of titania-based nanotubular oxide materials. The photocatalytic properties in the oxidation reactions of organic compounds and the performance characteristics of the memristive behaviour of TiO2-based nanotubular structures are considered in details. Their applications are discussed. The bibliography includes 238 references.

Composite ceramics of titanium nitride grains incorporated in an aluminium nitride matrix have been synthesized by high pressure high temperature treatment of a mechanical mixture of AlN–TiN (3 mol % TiN) powders. The microstructure of the samples analysed by means of electron beam microanalysis and Raman spectroscopy shows that the formation of cubic AlN in the composite begins near titanium nitride grains. The areas of mixed chemical composition, which can be assigned to the formation of the solid solutions Al1−xTixN, have been observed at the phase interfaces. The luminescence properties of AlN–TiN ceramics have been considered focusing on the choice of high pressure and high temperature treatment conditions. Three main components at 2.0 eV, 2.4 eV and 3.1 eV are revealed in the cathodoluminescence spectra analysed quantitatively. The observed emission originates from the radiative transitions with participation of valence band states, oxygen-vacancy centres (VAl–ON), nitrogen vacancies VN, and shallow donors which form a complex system of energy levels in the bandgap of the wurtzite-type AlN.

In this paper optical properties of microcrystalline HfO2 powder are investigated. X-ray diffraction and Raman spectroscopy were used to determine that the studied samples are in monoclinic phase. Based on the analysis of the diffuse reflectance spectra and applying Kubelka-Munk formalism we evaluated the indirect bandgap value Eg = 5.34 ± 0.05 eV. The calculated value is in agreement with independent data for HfO2 thin films synthesized by various methods. The paper is based on the materials of the report presented at the first Russian scientific confererence with the participation of the international community "YENISEI PHOTONICS – 2020"

Nanoferrites of Ni0.1Cu0.2MgxZn(0.7−x)Fe2O4 (x = 0.0, 0.15, 0.25, 0.35, 0.45, 0.55 and 0.70 wt%) system fabricated using flash auto combustion technique. All investigated samples annealed for 2 h at 600 °C. XRD, FTIR and TEM were utilized to evaluate the structural characterization of as-prepared samples. The electrical DC resistivity of the investigated samples is evaluated as a function of frequency and temperature. The initial magnetic permeability (μi) is dependent on the temperature and was measured at constant frequency 1 kHz and 10 kHz of the sinusoidal wave. A single-phase of spinel structure was formed and with increasing Mg content the peak (311) of 100% intensity decreases, which demonstrates the presence of Mg, which slows down the growth of the crystal as X-ray result. The FTIR spectra of the prepared ferrite samples are distinguished by the presence of two strong absorption bands (ν1 = 554 cm−1) and (ν2 = 449 cm−1). The morphological observation is determined by the transmission electron microscopy (TEM) and shows that the particles size ranged between 26 and 39 nm. It can notice shifted Curie temperature (Tc) to a higher temperature by increasing Mg content. Mass attenuation coefficient (μm), mean free path (λ), half value layer (X1/2), tenth value layer (X1/10) and effective atomic numbers (Zeff) for the studied samples, have been simulated using FLUKA (2020.0beta.2), while energy change from 15 × 10–3 to 153+ keV with increasing Mg concentration, both μm and Zeff decrease. The largest value of μm and Zeff when x = 0% while sample x = 0.35% has a minimum value of λ, X1/10 and X1/2.

NiFe2O4/PANI nano-composite with different polyaniline (PANI) content (25%, 50% and 75%) is synthesized. The NiFe2O4 (NF) is prepared by the flash auto combustion method and annealed at 400 °C for 2 h. The PANI is prepared by oxidative polymerization of aniline. The X-ray diffraction (XRD) technique confirmed that the NiFe2O4 particles are successfully dispersed in the PANI matrix with single phase structure. The characteristic absorption bands are observed from infrared (IR) spectra for the pure NF, pure PANI and their nano-composite. The dielectric constant ( $${\varepsilon }^{^{\prime}})$$ behavior of NF/PANI nano-composite at higher PANI content tends to be a polymer behavior. The Curie temperature decreased by increasing the PANI content and it is attributed to the basis of A-B exchange interaction due to the variation of $${Fe}^{3+}$$ content among the octahedral and tetrahedral sites. The values of the saturation magnetization (Ms), remanence magnetization (Mr), coercivity (Hc), area and squareness (Mr/Ms) are measured by using a vibrating sample magnetometer (VSM).

Zinc sulfide ZnS nanopowders were prepared by chemical deposition from aqueous solutions of zinc nitrate and sodium sulfide in the presence of sodium citrate or Trilon B. ZnS/Ag2S heteronanostructures were prepared by two-step chemical codeposition of zinc and silver sulfides. The prepared ZnS nanopowders had average particle sizes ranging from 2 to 10 nm depending on the reagent concentration ratio in the batch. The nanoparticle sizes in the thus-prepared heteronanostructures were 8–10 nm. The diffuse reflectance spectra of nanostructured ZnS and ZnS/Ag2S heteronanostructures were measured. The bandgap width Eg in the studied sulfide nanostructures was assessed based on an examination of the measured optical absorption spectra. As the nanoparticle size decreased from 10 to 2 nm, the Eg in ZnS nanopowders increased in the range 3.59–3.72 eV. The increasing Ag2S percentage in ZnS/Ag2S heteronanostructures leads to narrowing of the bandgap. Pulsed cathodoluminescence (PCL) spectra were recorded. The luminescence characteristics of ZnS and ZnS/Ag2S depend on the preparation method and nanoparticle morphology.

The mechanisms of photo- and thermoluminescence processes in cation-deficient submicron AlN crystals after UV excitation are studied. The observed emission spectra represent a superposition of bands peaking at 3.0 and 2.5 eV. These spectral features are related to electronic transitions with participation of ON impurity centers and oxygen–vacancy centers of the VAl–ON type. According to a quantitative analysis within the general-order kinetics formalism, charge carrier trapping centers based on nitrogen vacancies VN have an activation energy of 0.45 eV and are responsible for the formation of a thermally activated peak at a temperature of 345 K.

In order to increase the catalytic activity of titanium dioxide (TiO2) under visible light, a method for the synthesis of a complex sandwich catalyst based on nanotubular and sol–gel TiO2 and colloidal cadmium sulfide (CdS) was developed. The use of titanium dioxide in the form of nanotubes allowed increasing the specific surface area of the catalyst, which is one of the main factors in increasing the efficiency of the catalysis process. At the same time, the presence of CdS nanoparticles made it possible to widen the spectral range of irradiation used. Using the methods of X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy a comprehensive characterization of the synthesized samples was carried out. In addition, their chemical and phase composition, as well as the size of the nanoparticles and their morphology, were established. The photocatalytic activity was determined under the visible light and ultraviolet of nanostructures in reactions involving the oxidation of acetone in the gas phase.

Thermal quenching is one of the essential factors in reducing the efficiency of radiative processes in luminophores of various nature. The emission activity of low dimensional structures is influenced also by multiplicity of parameters that are related to synthesis processes, treatment regimes, etc. In the present work, we have investigated the temperature dependence of photoluminescence caused by exciton and defect-related transitions in ensembles of biocompatible InP/ZnS core/shell nanocrystals with an average size of 2.1 and 2.3 nm. The spread in the positions of energy levels is shown to be due to size distribution of quantum dots in the ensembles under study. For a quantitative analysis of the experimental data, we have proposed a band model accounting for the Gaussian distribution of the thermally activated barriers in the photoluminescence quenching processes. The model offers the thermal escape of an electrons from the core into the shell as the main mechanism for non-radiative decay of excitons. In turn, the quenching of defect-related emission is predominantly brought about through the emptying of the hole capture centers based on dangling phosphorus bonds. We have revealed the correlation between size distributions of quantum dots and scatter of the activation energy of exciton luminescence quenching. The developed approach will give further the possibility to optimize technological regimes and methods for band engineering of indium phosphide-based type-I quantum dots., Comment: 24 pages, 6 figures, 3 tables, 79 references. Keywords: quantum dots, core/shell, exciton and defect states, luminescence thermal quenching, inhomogeneous broadening, activation energy distribution

Ferroelectric samples Sr1−xBaxTiO3 (BST), where x = 0, 0.2, 0.4, 0.6, 0.8 and 1, were prepared using the tartrate precursor method and annealed at 1200 °C for 2 h. X-ray diffraction, “XRD”, pattern analysis verified the structure phase. The crystallite size of the SrTiO3 phase was calculated to be 83.6 nm, and for the TiO2 phase it was 72.25 nm. The TEM images showed that the crystallites were agglomerated, due to their nanosize nature. The AC resistivity was measured as temperature dependence with different frequencies 1 kHz and 10 kHz. The resistivity was decreased by raising the frequency. The dielectric properties were measured as the temperature dependence at two frequencies, 1 kHz and 10 kHz. The maximum amount of dielectric constant corresponded to the Curie temperature and the transformation from ferroelectric to paraelectric at 1 kHz was sharp at 10 kHz. Polarization–electric field hysteresis loops for BST samples were measured using a Sawer–Tawer modified circuit. It was shown that the polarization decreased with increasing temperature for all samples.

Thermoluminescence (TL) research provides a powerful tool for characterizing radiation-induced processes in extraterrestrial matter. One of the challenges in studying the spectral features of the natural TL of stony meteorites is its weak intensity. The present work showcases the capabilities of a high-sensitive original module for measuring the spectrally resolved TL characteristics of the Chelyabinsk and Tsarev chondrites. We have analyzed the emission spectra and glow curves of natural and induced TL over the 300 - 650 nm and RT - 873 K ranges. A quasi-continuous distribution of traps active within the 350 - 650 K range was found in the silicate substructure of both meteorites under study. Based on the general order kinetic formalism and using the natural TL data, we also estimated the activation energies of 0.86 and 1.08 eV for the Chelyabinsk and Tsarev chondrites, respectively., 7 pages, 4 figures, 2 tables, 18 references; Keywords: TL spectroscopy; ordinary chondrite; Chelyabinsk LL5; Tsarev L5; activation energy

The nonstoichiometric titanium dioxide nanotubular films were synthesized by the anodization of titanium foil in a solution of ethylene glycol and ammonium fluoride. The calcination of films at the temperatures of 200–600 °C led to the changes in their morphology, structure, phase composition, and properties. During the calcination, amorphous phase of titanium oxide in the prepared films was converted into anatase (space group I41/amd) at ca. 300 °C followed by the transformation of anatase to rutile (space group P42/mnm) at the temperatures above 500 °C. The optical band gap was decreased as the calcination temperature was increased due to the changes in stoichiometry and phase composition of nanotubular films. A complete mineralization of acetone vapor in a continuous-flow reactor using the nanotubular films was carried out for the first time. The photocatalytic activity of the film calcined at 500 °C in the reaction of acetone oxidation to carbon dioxide under visible light (λmax = 450 nm) was found to be 4 times higher than the activity of commercially available TiO2 P25. A high defectiveness and an extended surface were the reasons for an enhanced photocatalytic activity of the synthesized nanotubular films under visible light.

Photoluminescence properties and relaxation dynamics of electronic excitations in cesium vanadate CsVO 3 have been studied upon pulse laser excitation in the wide temperature range of 6.5–300 K. A vibronic structure observed in low-temperature PL spectra is considered and interpreted. Peculiarities of luminescence relaxation dynamics and emission spectra of CsVO 3 along with the appearance of the vibronic structure are explained in terms of strong electron-phonon coupling of excited electronic states and centrosymmetric vibrational modes in [VO 4 ] 3- center. A new approach in an interpretation of luminescence processes in vanadates is demonstrated. © 2019 Elsevier Ltd 16.5186.2017/8.9 The work was supported by Act 211 Government of the Russian Federation , contract № 02.A03.21.0006 . I.A.W. thanks for financial support Minobrnauki initiative research project № 16.5186.2017/8.9 . Authors thank Dr. Mathijs de Jong (Utrecht University) for his kind assistance in laser experiments and Prof. Boris V. Shulgin for fruitful discussions of this work.

With band-to-band (5.9 eV) excitation of a micropowder of hexagonal boron nitride with a content of carbon and oxygen impurities of ≤3.5 at. %, the peculiarities of the luminescence at 3.76 eV (330 nm) in the temperature range of 300–873 K have been studied. For thermally activated processes responsible for peaks at 331, 353 and 597 K in the spectral band, the kinetic parameters such as activation energy, the effective frequency factor, and kinetics order have been estimated. For this, curve fitting, the initial rise and “EA - Tstop” methods as thermally stimulated luminescence (TSL) techniques have been utilized. Analysis of the experimental temperature dependencies of the photoluminescence (PL) intensity has been carried out within the framework of the Mott relation with two independent quenching channels and taking the TSL contribution observed into account. The processes of PL temperature quenching have been shown to proceed by an external mechanism and to be characterized by energies of EQ = 1.43 and 1.39 eV. It has been concluded that the calculated values correlate with the level positions in the forbidden gap for two possible energy configurations of the CN-center for Μ- and Κ-valleys in the first Brillouin zone.

The h-BN microcrystalline powder with carbon and oxygen impurities have been studied at 83 and 296 K using Raman and photoluminescence (PL) spectroscopies. The observed blue shift of Raman peaks with temperature decreasing have been discussed. Two series of phonon replicas in PL emission spectra with a zero-phonon line at 4.08 eV have been registered under 4.28 eV excitation. The energy levels model of the impurity (CN-ON)-complex responsible for observe luminescence was proposed. It was shown that the optically active center retains its electroneutrality in the processes of radiative recombination under subband (in 4.28 eV) or band-to-band excitation. Possible mechanisms of electron-phonon scattering and phonon replicas forming under subband excitation of (CN-ON)-complex were analyzed. It was substantiated that at 83 K the longitudinal optical (ℏωLO = 174 meV) and transverse acoustic (ℏωTA = 60 meV) phonons at the middle points of high symmetry in the first Brillouin zone participate in the processes of intravalley (M- and Κ-scattering) and intervalley (Κ → Μ)-scattering, respectively.

Aluminum nitride crystals of regular geometric shape and with 0.1–2.0 μm size have been synthesized by original gas-phase technique. Using chemical composition analysis, the presence of main impurities of oxygen and silicon have been testified. The spectral features of cathodoluminescence (CL) and thermoluminescence (TL) under electron irradiation have been studied in grown AlN. It has been found that the measured CL and TL spectra have an almost identical form of single wide peak at 420 nm (2.95 eV), which can be approximated by superposition of three Gaussian components – weak 2.04 and 2.46 eV, predominant 2.87 eV. The possible origin of observed emissions has been discussed taking independent data into account. It has been found that 2.87 and 2.46 eV recombination processes occurred through electron transitions with participating of impurity ON and oxygen-vacancy centers (VAl-ON). 2.04 eV emission was caused by radiative transition between hole (VAl-ON)-levels and valence band. Analyzing measured three-dimensional TL dependence in AlN microcrystals after 14.6 kGy irradiation, it has been established that the maximum of the TL emission is observed at 420 nm and at a temperature of 345 K. Experimental TL curves have been described numerically in the frame of the general-order kinetic formalism with high accuracy to determine the activation energy EA = 0.58 eV of VN-trap which is responsible supposedly for the thermally stimulated emission observed. Taking calculated values of the kinetic parameters into account, it has been concluded that the recapturing of charge carriers to the indicated vacancy levels is characterized by a high probability in mechanisms of the radiation-stimulated response of AlN microcrystals irradiated with electrons.

The development prospects of memristive elements for non-volatile memory with use of the metal-dielectric-metal sandwich structures with a thin oxide layer are due to the possibility of reliable forming the sustained functional states with quantized resistance. In the paper we study the properties of fabricated memristors based on the non-stoichiometric $ZrO_2$ nanotubes in different resistive switching modes. Anodic oxidation of the $Zr$ foil has been used to synthesize a zirconia layer of $1.7$ $\mu$$m$ thickness, consisting of an ordered array of vertically oriented nanotubes with outer diameter of 75 nm. $Zr/ZrO_2/Au$ sandwich structures have been fabricated by mask magnetron deposition. The effects of resistive switching in the $Zr/ZrO_2/Au$ memristors in unipolar and bipolar modes have been investigated. The resistance ratios $\geq3\cdot10^4$ between high-resistance (HRS) and low-resistance (LRS) states have been evaluated. It has been founded the conductivity of LRS is quantized in a wide range with minimum value of $0.5G_0=38.74$ $\mu$$S$ due to the formation of quantum conductors based on oxygen vacancies ($V_O$). Resistive switching mechanisms of $Zr/ZrO_2/Au$ memristors with allowing for migration of $V_O$ in an applied electric field have been proposed. It has been shown that the ohmic type and space charge limited conductivities are realized in the LRS and HRS, correspondingly. We present the results which can be used for development of effective memristors based on functional $Zr/ZrO_2/Au$ nanolayered structure with multiple resistive states and high resistance ratio., Comment: 24 pages, 8 figures, 1 table, 78 references

Titanium dioxide (TiO2) was synthesized by sol-gel method at different values of pH = 3, 7, 8, 9, or 10. X-ray phase analysis has shown that in an acid rout, an anatase phase had crystallized, and in an alkaline rout an amorphous phase of TiO2 was achieved. After annealing for 4 hours at 350∘C, all samples were transformed into anatase phase. The particle size in the different samples varies from 7 to 50 nm depending on the pH. The diffuse reflectance spectra revealed a high value of the band gap width in the range from 2.9 to 3.4 eV and its narrowing after annealing to the range from 2.8to 3.1 eV. The specific surface area measured by BET method was changing from 80 up to 140 m2 /g. The work was carried out according to the state assignment for IMET UB RAS and ISSC UB RAS. I.A. Weinstein thanks Minobrnauki initiative research project № FEUZ-2020-0059 for financial support.

The chapter summarizes research results on temperature evolution of optical absorption spectra in a wide temperature range of 6.5–296 K for colloidal core/shell InP/ZnS quantum dot ensembles with a different size distribution. Exciton–optical transition energies in the InP core and ZnS shell were determined by the second-order derivative spectrophotometry. Numerical analysis within the frame of linear exciton–phonon coupling showed that the shifts of the observed spectral maxima with temperature were due to the interaction of excited states with longitudinal acoustic vibrations. It was established that the half-width of the spectral bands remained unchanged, which indicated the inhomogeneous broadening effect and a high degree of static disorder in the ensembles under study. The semi-phenomenological model was proposed that took into account the effects of the exciton–phonon interaction and allowed one to analyze the influence of the static and dynamic types of atomic disorder on behavior of optical absorption spectra in InP/ZnS quantum dots under temperature variation.

In the present work we have synthesized nanotubular TiO2 film with a nonstoichiometric layer in the vicinity of titanium foil by anodization during 120 min. The catalytic activity of nanotubular titanium dioxide films formed during the oxidation of acetone to carbon dioxide under the action of visible light with a wavelength of 450 nm was found to be approximately 2 times higher compared to standard titanium dioxide (Degussa P25). Such a pronounced enhancement of activity may be attributed to a more efficient absorption of visible light by the films due to narrowing of the optical gap because of difference in the nonstoichiometry of titanium dioxide near the interface between nanotubular film and the titanium foil substrate. Keywords: photocatalysis, nonstoichiometric titanium dioxide, purification of water

Photoluminescence (PL) thermal quenching of InP/ZnS core/shell nanocrystals of 4.2 (QD-1) and 4.6 (QD-2) nm in diameter is investigated in the temperature range of 6.5-296 K. Observed PL spectra are found to originate from exciton and defect-related transitions. Temperature behavior of the emission bands indicates effects of inhomogeneous broadening due to distributions of quantum dots parameters in the ensembles. PL thermal quenching analysis unveils two non-radiative relaxation channels for each band in both samples. Activation energies of 130 and 119 meV in QD-1 and QD-2, correspondingly, for the exciton band can be assigned to the bright-bright splitting of the exciton fine structure. © Published under licence by IOP Publishing Ltd. Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCIAS): 727-2015 Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCIAS) We gratefully acknowledge the financial support received from the Departamento Administrativo de Ciencia, Tecnología e Innovación, Colciencias, Colombia, through Convocatoria No. 727-2015. The authors would also like to thank the administrative support received from the Centro de Investigación para el Desarrollo y la Innovación (CIDI) of the Universidad Pontificia Bolivariana.

Nano PbZr0.52Ti0.48O3-ordinary Portland cement (PZT-OPC) composites were fabricated by a ball milling technique with different PZT content (30, 50, 70, and 90% by weight). The prepared samples were annealed at 600 °C. The structure, morphology, thermal and electrical properties of these annealed samples were investigated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). The effects of PZT on dielectric and piezoelectric properties of the composites were investigated. γ-ray spectroscopy was used to measure the γ-ray attenuation coefficients of the annealed nanocomposite samples using the 661.7 keV γ-ray of 137Cs source. The microstructure changes of the prepared composite samples were investigated using the positron annihilation lifetime (PAL) and Doppler broadening (DB) techniques. The XRD patterns show both PZT and cement peaks. Also, these patterns indicate the presence of PZT retards the hydration process of the Portland cement. The FTIR spectra show the major absorption bands for both PZT and cement. SEM images show the binding between calcium silicate hydrate and PZT which may be a better factor for improving the mechanical properties of the cement. TGA curves show a higher thermal weight loss for 50% PZT-OPC composite sample. The PZT-OPC composite sample with 50% PZT content shows the highest γ-ray mass attenuation coefficient compared with the other composite samples. The positron annihilation spectroscopy (PAS) results show that the size of large voids and the concentration of small defects increase by increasing PZT content. Also, these results reveal that the core electrons slightly reduced by increasing PZT content. The results indicate that the dielectric constant and piezoelectric coefficient values slightly and rapidly increase for composite samples with PZT content 50%, respectively. Finally, the 50% PZT-OPC composite sample showed novel shielding and acceptable piezoelectric properties to be used as a smart shield.

Long-lasting luminescence in excited solid-state composites is of considerable interest as an inner light source for perspective materials capable to generate self-induced photoactivity after external irradiation turn-off. The corresponding slow ultraviolet (UV) and visible (Vis) emissions in hexagonal boron nitride can be caused by technology induced impurities (oxygen, carbon etc.) which form the complex system of electron and/or hole capturing levels within the energy gap. As result the created charge traps substantially influence on functional properties and optoelectronic characteristics of developed heterostructures based on h-BN. In this paper we study the photoluminescence (PL) peculiarities of nanostructured crystalline h-BN powder with C and O content

Particulars of the UV-irradiated h-BN micropowder were studied by the means of spectrally resolved thermoluminescence (TL) technique. Using curve fitting, peak shape, various heating rates and initial rise methods an estimation of kinetic parameters (activation energy, effective frequency factor and kinetics order) for the active capture centers, forming the complex multitrap system, was performed. It is shown that TL in 380 and 425 nm bands is caused by the radiative transitions of electrons from 1B- and 3B-centers levels with 0.7 and 1.2 eV energy below the bottom of conduction band to the carbon levels (C N -centers) with the activation energy of 1.4 eV above the top of valence band, respectively. The consideration of temperature quenching of luminescence in the evaluation of traps activation energy is analyzed. It is found that, under the thermal activation of electron (1B- and 3B-centers) and hole (C N - centers) traps, the TL processes of first and second kinetics order dominate respectively. A mechanism of electron tunneling from the deep traps to 1B- and 3B-centers in h-BN following the registered TL processes is being discussed. An energy-level diagram describing the thermally stimulated mechanisms of charge carriers redistribution was proposed for the UV-irradiated h-BN.

A thermal quenching effect of luminescence was studied in nanostructured compacts of monoclinic zirconium dioxide obtained by cold pressing of nanopowders. The dependence of PL intensity at 480 nm emission band on temperature was found experimentally. It was established that TL quenching causes the drop of lightsum in 390 and 485 К peaks with a growing heating rate. TL kinetic parameters values of these peaks were calculated by different methods. A simulation of lightsum dependences of the above mentioned TL peaks on the heating rate was carried out. The mechanism of luminescence thermal quenching, taking into account not only intracentral but also external electronic processes of charge transfer, is justified for monoclinic ZrO2.

The optical-absorption spectra of InP/ZnS (core/shell) quantum dots have been studied in a broad temperature range of T = 6.5–296 K. Using the second-order derivative spectrophotometry technique, the energies of optical transitions at room temperature were found to be E 1 = 2.60 ± 0.02 eV (for the first peak of excitonic absorption in the InP core) and E 2 = 4.70 ± 0.02 eV (for processes in the ZnS shell). The experimental curve of E 1(T) has been approximated for the first time in the framework of a linear model and in terms of the Fan’s formula. It is established that the temperature dependence of E 1 is determined by the interaction of excitons and longitudinal acoustic phonons with hω = 15 meV.

The short Communication based on results of notes: Andre Geim "When lost in a multiverse" (Nat. Phys. 13, 1142 (2017)) and Klaus von Klitzing "Metrology in 2019" (Nat. Phys. 13, 198 (2017)), Comment: 5 pages, 1 figure, 10 references

In this work, we have simulated the processes of broadening the first exciton band in optical absorption spectra (OA) for InP/ZnS ensembles of colloidal quantum dots (QDs). A phenomenological model has been proposed that takes into account the effects of the exciton&ndash, phonon interaction, and allows one to analyze the influence of the static and dynamic types of atomic disorder on the temperature changes in the spectral characteristics in question. To vary the degree of static disorder in the model system, we have used a parameter &delta, which characterizes the QD dispersion in size over the ensemble. We have also calculated the temperature shifts of the maxima and changes in the half-width for the exciton peaks in single nanocrystals (&delta, = 0), as well as for the integrated OA bands in the QD ensembles with different values of &delta, = 0.6&ndash, 17%. The simulation results and the OA spectra data measured for InP/ZnS nanocrystals of 2.1 nm (&delta, = 11.1%) and 2.3 nm (&delta, = 17.3%), are in good mutual agreement in the temperature range of 6.5 K&ndash, RT. It has been shown that the contribution of static disorder to the observed inhomogeneous broadening of the OA bands for the QDs at room temperature exceeds 90%. The computational experiments performed indicate that the temperature shift of the maximum for the integrated OA band coincides with that for the exciton peak in a single nanocrystal. In this case, a reliable estimate of the parameters of the fundamental exciton&ndash, phonon interaction can be made. Simultaneously, the values of the specified parameters, calculated from the temperature broadening of the OA spectra, can be significantly different from the true ones due to the effects of static atomic disorder in real QD ensembles.

The catalytic activity of nanotubular titanium dioxide films formed during the oxidation of acetone to carbon dioxide under the action of visible light with a wavelength of 450 nm was found to be approximately 2 times higher compared to standard titanium dioxide (Degussa P25). The nanotubular films were grown by the anodization of titanium foil using an original technique. Diffuse reflectance spectra of the films are attributed to enhanced activity in the visible spectrum by the nonstoichiometry of titanium dioxide near the interface between the nanotubular film and the titanium foil substrate., Comment: 10 pages, 9 figures, 1 Table, 43 references

The temperature dependence of the photoluminescence (PL) intensity of 3.90 eV in microcrystalline hexagonal boron nitride is studied in the range of 7–1100 K. The results obtained have been analyzed within the band model of energy levels of donor-acceptor pairs based on impurity (ON CN) complexes. Luminescence enhancement processes at T 220 K, when directly excited, the samples diminish the PL intensity because of the processes of thermal ionization of the donor level of the ON-center (122 meV) and the deep acceptor level of the CN-center (1420 meV) as parts of the (ON CN)-complex. In this case, the temperature enhancement region with an activation energy of 15 meV is due to the decay of a bound Wannier-Mott exciton followed by transfer of excitation to the associated donor-acceptor pair. With band-to-band excitation at T > 220 K, the temperature peculiarities of the PL under study are determined by non-radiative relaxation processes with activation energies of 57 and 252 meV, which are caused by shallow donor levels of VN- and ON-centers, respectively.

The high-field electroluminescence (EL) spectra for Al-rich AlN nanowhiskers varying applied voltage were studied. The observed 2.70 eV emission, which can be considered as superposition of two Gaussian bands in 2.75 and 2.53 eV, was analyzed. It was shown that Fowler-Nordheim effect took place in EL mechanism with participation of capturing levels of O N - and V N -centers when AlN nanowhiskers were exposed to an external field of 2.5 ÷ 10 V/μm. Obtained results and made conclusions are in a good agreement with independent electron field emission measurements for different one-dimensional AlN nanostructures.

Thermoluminescence (TL) response of h-BN micropowder, characterized by two peaks near 337 and 584 K, was studied in the 380-nm band after excitation with monochromatic ultraviolet radiation (UVR). On the basis of the obtained results and independent data analysis, assumptions were made on the mechanisms of donor–acceptor recombination with the participation of 1B, O N, and C N centers, responsible for the observed thermally activated emission. TL excitation spectra in the 200–380-nm range were analyzed. It was observed that the resolved maxima correspond quite to the characteristic wavelengths of 260 nm (maximum bactericidal efficiency) and 297 nm (maximum skin erythema). It is found that the dose dependence for an integral intensity of high-temperature peak is linear in the suberythemal range of 0.01–0.35 mJ/cm 2 .

ZnS nanopowders have been synthesized by chemical deposition from aqueous solutions of zinc nitrate and sodium sulfide in the presence of sodium citrate or Trilon B. Ag2S/ZnS heteronanostructures have been prepared by co-deposition of zinc and silver sulfides. The size of nanoparticles in the deposited powders has been estimated by X-ray diffraction and transmission electron microscopy. A change in the ratio between the concentrations of reagents in the reaction mixtures made it possible to obtain ZnS nanopowders with an average particle size of 2–10 nm. The size of the nanoparticles in the prepared heteronanostructures is 8–10 nm. The diffuse reflection spectra have been measured and the corresponding absorption spectra of nanostructured ZnS and Ag2S/ZnS heteronanostructures have been analyzed using Tauc plots. The optical band gap Eg of the studied sulfide nanostructures has been estimated. A blue shift of the optical absorption edge and an increase in the Eg values from 3.59 to 3.72 eV are observed with a decrease in the size of ZnS nanoparticles. An increase in the Ag2S content in Ag2S/ZnS heteronanostructures leads to a decrease in the optical band gap. Pulsed cathodoluminescence of nanostructured ZnS and Ag2S/ZnS heteronanostructures have been investigated. It is found that the maxima of the luminescence spectra of nanostructured zinc sulfide are located at about 450 nm. Prepared samples of nanostructured ZnS possess a very short decay time and thanks to this property the prepared ZnS nanostructures can be used as a material for scintillation detectors.

Zirconia nanotubular layer with an outer tube diameter « 25 nm was synthesized by potentiostatic anodization. The Zr/ZrO 2 -NT/Au memristive structure is fabricated using stencil mask and magnetron sputtering techniques. Current-voltage characteristics are measured in full cycles of resistive switching with varying parameters of the applied harmonic voltage. An equivalent circuit with unidirectional electrical conductivity for the studied structure is proposed. Estimates of the electrical resistance of memristors in high- and intermediate resistivity states are performed. The high synaptic plasticity of memristors based on the Zr/ZrO 2 -NT/Au structure is shown.

Self-ordered nanotubular titania TiO 2 -NT with outer tube diameter of 45 nm are synthesized using the anodic oxidation of titanium foil. Four sets of memristors with 100 μm diameter based on Ti/TiO 2 -NT/Au sandwich structures with an oxide layer thickness of 80, 120, 160 and 200 nm are fabricated. Current-voltage (CV) characteristics for the obtained samples in the static and dynamic operation modes are studied. Resistance in high and low resistance states is estimated. Basing on the analysis of the CV characteristics in dynamic mode (> 14 000 switchings) a prospective of use for synthesized Ti/TiO 2 -NT/Au micromemristors with oxide layer thickness of 160 nm in non-volatile memory is shown.

Optical absorption (OA) and photoluminescence (PL) spectra of InP/ZnS core/shell nanocrystals with 2.3 nm average size were investigated in the temperature range of 6.5–296 K. Using second derivative spectrophotometry technique energies of the OA transitions at 296 K in quantum dot (QD) solutions and films are evaluated to be E 1 = 2.37, E 2 = 4.10 and E 3 = 4.68 eV. Temperature shifts of the E 1 and E 2 levels are found to result from interaction with effective phonons of 59 and 37 meV energies, respectively. Herewith the 370 meV half-width of the first exciton absorption peak remains constant due to the dominance of inhomogeneous broadening effects caused by QD parameters distribution. Measured PL spectra have a complex structure and can be described in 6.5–296 K range by two independent Gaussian components associated with exciton and defect-related states. In addition, Stokes shift of 320 meV is observed to decrease at T > 200 K. PL thermal quenching analysis in frame of Mott mechanism points to presence of non-radiative relaxation channel with an activation energy of 74 meV.

Nanoporous anodic alumina membranes were synthesized in HF, (COOH)2, H3PO4 and H2SO4 electrolytes. It was shown that characteristic blue emission had the same origin in all samples and was caused by F-type anion centers.

Thermally stimulated luminescence (TSL) excitation and emission processes in h-BN nanopowders after UV irradiation were studied. TSL showed the highest response within the 5.4 eV band. 3.0 and 3.9 eV bands, resulting from the radiative donor-acceptor recombination between the electron (1B-H O N -centers) and the hole traps (CN-center), were found. TSL curves quantitative analysis in the context of general order kinetics was made. It was shown that 1B-centers had 0.850.05 eV activation energy and were responsible for the TSL peak at 35010 K. Band structure for TSL excitation and emission mechanisms in h-BN nanopowder was suggested. © Published under licence by IOP Publishing Ltd.

Registration of thermoluminescence (TL) spectra technique for irradiated samples in Perkin Elmer LS 55 spectrometer using developed high-temperature accessory during single heating cycle is shown. Functionality of serial instrument for RT–773 K temperature range is significantly widen. Spectrally resolved TL dependencies for h-BN micropowders and bulk AlN single crystals following UV irradiation are studied. TL spectral features of h-BN powders, synthesized by carbamide and plasma-chemical techniques, are determined and quantified. It is shown that the difference between TL curves obtained by the described and the standard modes does not exceed 10%.

Multi walled carbon nanotubes were used for modification of thick-film carbon-containing electrodes for adsorptive stripping voltammetry. A complex compound of Fe(III) with pyrocatechol was chosen as model system. As compared to the electrodes fabricated without using carbon nanotubes, the modified ones have the recovery close to 100%, 2 times higher sensitivity, and 3 times lower limit of detection. The developed sensors can be used for quick determination of trace amounts of iron in real objects.

AlN nanowhiskers with an average diameter of 68 nm, for which a chemical analysis showed an Al: N ratio of about 1: 0.8 and a high content of oxygen and carbon impurities, have been synthesized. The electroluminescent properties of the nanostructures have been studied at room temperature in the spectral range of 4.0–1.77 eV (310–700 nm) at varied voltage (75–200 V) and frequency (0.5–10.0 kHz) of the exciting harmonic signal. It is shown that the electroluminescence recorded in the blue spectral range is constituted by bands peaked at E max ≈ 2.53 and 2.75 eV and half-widths ω ≈ 0.39 and 0.30 eV, respectively, which may be associated with electron-optical transitions involving impurity-vacancy centers in the anion and cation sublattices of AlN.

Spectra of the cathodoluminescence (CL) of single crystals and micropowders of AlN are studied. It is shown that bands with maxima at 3.2, 2.7 and 2.1 eV can be observed in the CL. The peaks at 2.7 and 3.2 eV are associated with ON centers and complexes of the type (VAl-ON); the 2.1 eV band is due to recombination processes involving cation vacancies. The narrow CL peak at 1.77 eV is also observed for AlN powder and is attributed to Cr3+ impurities.

The principles for the application of methods of optically stimulated luminescence (OSL) in a scanning electron microscope (SEM) were developed in this work. A functional scheme for a diagnostic OSL attachment for the investigation of the local properties and distribution parameters of optically active structure complexes in wide-gap dosimeter materials was proposed. Analysis of the dependencies of OSL on the variation in the size of regions that are irradiated with electrons was conducted with anion-defective α-Al2O3 singlecrystals as an example. The possibility of OSL diagnostics of the surface of solid luminescent media and functional matrices with a microscale spatial resolution was shown.

Diffuse reflectance spectra of h-BN nanostructured powder were analyzed using the Kubelka-Munk approach. Under the assumption of direct allowed transitions, the energy gap width of Eg = 5.41 eV was estimated. It was shown the observed spectral features near the fundamental absorption edge were caused by the carbon impurity and were in satisfactory agreement with known independent data.

A layer of titanium dioxide (TiO2-NT) nanotubes 500 nm thick with average diameters of 60 nm is grown via anodizing. Memristive behavior typical of synthesized Ti/TiO2-NT/Au structures is observed in full cycles of resistive switching, and during the multiple reading of data. Impedance in the states of low (R LRS ≈ 3 Ohm) and high (R HRS ≈ 180 Ohm) resistance are estimated for the obtained memristors.