Bismuth-based compounds are widely used as superconductors, catalysts and materials for optical devices. Their properties, and the possibility of controlling these properties, are determined by their electronic structure and the local environment of the Bi-centres. Although X-ray spectroscopy is a powerful method for revealing crystal and electronic structure, the results obtained so far have been limited by the energy resolution of the experimental data. Here, for the first time, we report X-ray absorption near edge structure (XANES) data, recorded in high energy resolution fluorescence detection (HERFD) mode at the Bi LIII and LI edges for a number of bismuth compounds. Experimental data are analysed using ab initio calculations based on a finite difference method (FDMNES) code, for metallic Bi, Bi2O3, BiPO4, Bi4(GeO4)3 and NaBiO3 compounds. It was observed that both the oxidation state and the length of the Bi-ligand bonds determine the exact position of the absorption edge, and this is in good agreement with other studies. Additionally, due to the high energy resolution, spectral features corresponding to strong Bi p-d orbital mixing were resolved. The results obtained here can be used as input for further investigations of the electronic structure of bismuth compounds in different chemical states.

Hydrated lanthanum fluoride powders, both undoped, and doped with erbium and ytterbium fluorides (to a total content of 6–28 mol %), of the general formula RF 3 · n H 2 O ( n = 0.30 ± 0.01), crystallizing in the hexagonal system, were obtained by coprecipitation from aqueous solutions of the corresponding nitrates by the interaction with hydrofluoric acid. The dehydration is completed at 380°C. At 600°C, the concentrated solid solution decomposes to precipitate a phase with the structure of orthorhombic YF 3 . The efficiency of the upconversion luminescence of the powders, excited at a wavelength of 974 nm, is low.

Hydrated lanthanum fluoride powders, both undoped, and doped with erbium and ytterbium fluorides (to a total content of 6–28 mol %), of the general formula RF3 · nH2O (n = 0.30 ± 0.01), crystallizing in the hexagonal system, were obtained by coprecipitation from aqueous solutions of the corresponding nitrates by the interaction with hydrofluoric acid. The dehydration is completed at 380°C. At 600°C, the concentrated solid solution decomposes to precipitate a phase with the structure of orthorhombic YF3. The efficiency of the upconversion luminescence of the powders, excited at a wavelength of 974 nm, is low.

⎯Hydrated lanthanum fluoride powders, both undoped, and doped with erbium and ytterbium fluorides (to a total content of 6–28 mol %), of the general formula RF3 · nH2O (n = 0.30 ± 0.01), crystallizing in the hexagonal system, were obtained by coprecipitation from aqueous solutions of the corresponding nitrates by the interaction with hydrofluoric acid. The dehydration is completed at 380°C. At 600°C, the concentrated solid solution decomposes to precipitate a phase with the structure of orthorhombic YF3. The efficiency of the upconversion luminescence of the powders, excited at a wavelength of 974 nm, is low. DOI: 10.1134/S0036023618030130 One of the intensely developed fields of photonics is the creation of efficient upconversion phosphors based on f luorides. Upconversion phosphors, which were first proposed by Ovsyankin and Feofilov [1] and Auzel [2], convert IR pump radiation to luminescence in the visible region. These phosphors are most actively studied for biomedical applications because they allow one to irradiate tissues within the tissue transparency window (~1 μm) and to detect the luminescence of particles inside cells in the range where the tissues are nontransparent (visible region) [3–7]. A most widely used matrix for upconversion phosphors is the hexagonal phase and the cubic phase that form in the NaF–YF3 system and are denoted by NaYF4 [2, 8–10]. We showed [11, 12] that quite an efficient upconversion phosphor is strontium fluoride doped with ytterbium and erbium, which demonstrates a very high (>6%) luminescence energy yield. This stimulates the search for new matrices [13]. A phosphor that seems to be promising for these purposes is LaF3:Yb,Er, which was investigated previously [14–20], including biomedical applications [21]. However, luminescence efficiency issues, including the effect of the concentration of activators on this efficiently, remained unstudied. Fluoride powders can be synthesized by various methods [22–24]: sintering [15], thermal decomposition (pyrolysis) of precursors, mechanochemical synthesis, electrodeposition, hydrothermal [18] and solvothermal methods, interaction with ammonium fluoride or bif luoride [25], gas-phase chemical reactions with the participation of the vapor phase [26], interaction of sulfides with hydrofluoric acid [27], and crystallization of glasses [20, 28], but the simplest method is precipitation from aqueous solutions [16, 19, 29, 30]. Previously [31, 32], it was shown that, in precipitation from aqueous solutions, yttrium subgroup element trif luorides primarily crystallize not as trif luorides but as intricate complexes (H3O)R3F10 ⋅ nH2O with a characteristic particle size of ~3 μm. Cerium subgroup element f luorides crystallize as trif luorides with the LaF3 (tysonite) structure with a characteristic particle size of 10–60 nm [24, 29, 32, 33]. The purpose of this work was to study the synthesis and luminescence characteristics of lanthanum fluoride powders doped with ytterbium and erbium. EXPERIMENTAL The initial substances were lanthanum nitrate hexahydrate, ytterbium nitrate hexahydrate, and erbium nitrate pentahydrate (99.99 pure) (OOO LANHIT, Russia), and also hydrofluoric acid (special-purity grade 27-5) and double distilled water. The reagents were not additionally purified. Fluoride powders were precipitated from aqueous solutions as follows. Aqueous solutions of rare-earth element nitrates (0.05 mol/L) and hydrofluoric acid (26 mol/L) were prepared. The acid was taken in a fivefold excess of its stoichiometric amount calculated by the reaction R(NO3)3 + 3HF → RF3↓ + 3HNO3.

Исследован синтез образцов твердого раствора Sr1-x-yYbxTmyF2+x+y (x = 0.010–0.300; y = 0.001–0.060) при использовании различных методик осаждения: прямое, обратное и совместное осаждение исходных растворов, а также различных фторирующих агентов (фторид аммония и фтороводородная кислота). В результате исследования при использования NH4F было обнаружено, что при прямом и обратном осаждении в концентрационном диапазоне 0.10

Исследован синтез образцов твердого раствора Sr1-x-yYbxTmyF2+x+y (x = 0.010–0.300; y = 0.001–0.060) при использовании различных методик осаждения: прямое, обратное и совместное осаждение исходных растворов, а также различных фторирующих агентов (фторид аммония и фтороводородная кислота). В результате исследования при использования NH4F было обнаружено, что при прямом и обратном осаждении в концентрационном диапазоне 0.10<x+y<0.24 существует область фазового расслоения, где образуются структурно идентичные твердые растворы с малым различием в параметре решетки. Термообработка при 600 oС приводит к спеканию твердых растворов с выравниваем состава. При совместном осаждении синтезируются однофазные образцы. При использовании в качестве фторирующего агента фтороводородной кислоты фазовое расслоение двух структурно идентичных твердых растворов приводит к значительным различиям параметров решетки, выравнивания состава при данной термообработке не происходит. Авторы благодарят А.Е. Баранчикова и В.К. Иванова за характеризацию образцов методом сканирующей электронной микроскопии. Работа выполнена при финансовой поддержке гранта РФФИ № 16-32-00654-мол_а.

The paper presents the research of chemical and phase composition of the zone of diffusion interaction in the layered composite Cr20Ni80-AD1. It is shown that interlayer border of bimetal Cr20Ni80-AD1 is a complex mixture of phases with the main phases in its composition in solid-phase interaction: Al3Ni2 and Al14.687Cr3.443Ni0.87, and in the liquid phase Al3Ni2, Al0.987Cr0.017, Al14.687Cr3.44Ni0.87 and Al45Cr7. It is shown, that conditions of holding time of the heat treatment do not affect the phase and chemical composition of the diffusion zone.

Heterogeneous oxidative chlorination of methane was investigated. The target product is methyl chloride. The investigated terms and conditions of oxychlorination of methane: process temperature 400°C, pressure 0.1-0.9 MPa, catalyst (% weight.): copper chloride (II) 1-8%; potassium chloride 2.5%; lanthanum chloride 1%; carrier - aluminosilicate. Powder X-ray diffractometry and electron microscopy showed that the active catalyst components (CuCl2, KCl, LaCl3) are unevenly distributed on the support surface (α-Al2O3·SiO2) and form agglomerates with a high salt content, including binary chlorides such as KCuCl3, K2CuCl3 or K2CuCl4, hydrates K2CuCl4·2H2O and CuCl2·2H2O and hydroxychlorides Cu3Cl4(OH)2 and Cu2Cl(OH)3. The kinetics of methane oxychlorination was studied in a gradientless reactor at 400°C and pressure 0.1 - 0.9 MPa by varying the partial pressures of the reactants. Analysis of the products was carried out by GC. An equation of the reaction rate including partial pressures of methane, hydrogen chloride and water to the 0.77, 0.01 and 0.64 power, respectively, but of zero order by oxygen and chlorine provides an adequate description of methyl chloride formation rate. Significant influence of water partial pressure is proved for the reaction under consideration.

Heterogeneous oxidative chlorination of methane was investigated. The target product is methyl chloride. The investigated terms and conditions of oxychlorination of methane: process temperature 400°C, pressure 0.1-0.9 MPa, catalyst (% weight.): copper chloride (II) 1-8%; potassium chloride 2.5%; lanthanum chloride 1%; carrier - aluminosilicate. Powder X-ray diffractometry and electron microscopy showed that the active catalyst components (CuCl2, KCl, LaCl3) are unevenly distributed on the support surface (α-Al2O3·SiO2) and form agglomerates with a high salt content, including binary chlorides such as KCuCl3, K2CuCl3 or K2CuCl4, hydrates K2CuCl4·2H2O and CuCl2·2H2O and hydroxychlorides Cu3Cl4(OH)2 and Cu2Cl(OH)3. The kinetics of methane oxychlorination was studied in a gradientless reactor at 400°C and pressure 0.1 - 0.9 MPa by varying the partial pressures of the reactants. Analysis of the products was carried out by GC. An equation of the reaction rate including partial pressures of methane, hydrogen chloride and water to the 0.77, 0.01 and 0.64 power, respectively, but of zero order by oxygen and chlorine provides an adequate description of methyl chloride formation rate. Significant influence of water partial pressure is proved for the reaction under consideration.

We have studied TiO2, Ag, Ag/TiO2, and Cu/TiO2 coatings grown on track-etched polyethylene terephthalate membranes. The metals and oxides were deposited by reactive vacuum sputtering using a planar magnetron. The microstructure of the samples were examined by scanning and transmission electron microscopy techniques. The elemental composition of the coatings were determined by energy dispersive X-ray microanalysis, and their phase composition was determined by X-ray diffraction at different temperatures and by transmission electron diffraction. Titanium dioxide can be present on the surface of track-etched membranes (TMs) in three forms: nanocrystals of tetragonal anatase with orthorhombic brookite and amorphous TiO2 impurities. The copper-metallized TM has been shown to contain cubic Cu2O. The optical properties of the composite membranes and films have been studied by absorption spectroscopy. The energies of direct and indirect allowed optical transitions have been evaluated from measured absorption spectra of the TiO2, Ag/TiO2, and Cu/TiO2 coatings.

In this paper, we describe the use of self-fluorinating conditions for the thermal treatment of Sr1-x-y-zYbxEry(NH4)(z)F2+x+y-z precursor for the preparation of high-efficiency SrF2:Yb:Er up-converter powders. We report actual SrF2:Yb:Er compositions with up-conversion efficiencies exceeding 4% (pumping power 1 W/cm(2) at 974 nm wavelength) and describe the synthesis of ceramics with higher than 80% transmittance at 0.42-7.0 mu m. The latter ceramics can be used as a potential IR radiation visualizer. For the first time, we present an analysis of correlation between up-conversion luminescence energy yield and specimen composition for SrF2:Yb:Er nanopowders. Taking into account the observed erbium ion up-conversion luminescence in the red part of the visible spectrum, we recommend certain SrF2:Yb:Er compositions for practical application in photodynamic cancer therapy. (C) 2016 Elsevier B.V. All rights reserved.

•Glass samples of [GeSx]90I10 (x=1.5, 1.7, 2.0, 2.3, 2.45, 2.6) compositions were prepared.•Optical, thermal properties and crystallization ability of [GeSx]90I10 glasses were investigated.•For the first time, Ge–S–I glass fibers were produced.

Divalent tin-containing germanate glasses have demonstrated wide photoluminescence similar to that of tin silicate glasses discovered recently. In comparison with silicate glasses, the germanate glasses are characterized by longer emission lifetimes (145 ÷ 440 µs), emission peaking at 1.59 ÷ 1.64 µm and the absence of SnO disproportionation into SnO2 and Sn during glass synthesis. The potential fabrication of optical fiber via the SnC2O4 + GeO2 powder in silica tube method was demonstrated.

The composition of silicate oxide glass and the synthesis and heat-treatment regimes in which bismuth selenide nanocrystals form in the glass are found. The crystalline phase of bismuth selenide nanocrystals with characteristic size about 20 nm is identified by three different methods: x-ray structural analysis, Raman scattering, and electronic microscopy. Data are presented on the absorption spectra of the experimental glass samples in the range 400 – 3300 nm.

CsI, CsBr and GaAs thin films have been grown by pulsed laser deposition on glass substrates. The morphology and structure of the films have been studied using X-ray diffraction and scanning electron microscopy. The CsI and CsBr films were identical in stoichiometry to the respective targets and had a polycrystalline structure. Increasing the substrate temperature led to an increase in the density of the films. All the GaAs films differed in stoichiometry from the target. An explanation was proposed for this fact. The present results demonstrate that, when the congruent transport condition is not fulfilled, films identical in stoichiometry to targets can be grown by pulsed laser deposition in the case of materials with a low melting point and thermal conductivity.

We have developed a synthetic protocol for the preparation of SrF2-based Yb3+/Er3+/Tm3+-coactivated nano-crystalline white light luminophores by co-precipitation from aqueous solutions and have achieved a good level of sample homogeneity in the course of their preparation. We established that the particle size and morphology of the precipitated nanopowders were essentially independent from the fluorinating reagent used, the starting materials' ratio and the conditions of thermal treatment. We achieved the target white light luminescence for Sr1−x(Yb/Er/Tm)xF2+x specimens with the best results obtained for the Sr0.785Yb0.200Er0.010Tm0.005F2.215 sample at 400 mW pumping power (λ = 974 nm).