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The phase diagram of the SrF2–MgF2 system has been studied by differential thermal analysis (DTA) and X-ray powder diffraction (XRD). The stability area of the compound SrMgF4 is very small, and its extent is about 20°С between 870 and 890°С. The formation of compounds by magnesium fluoride and strontium fluoride with other metal fluorides is considered in the M versus X coordinates, where M is the cumulative moment of the cation and X is the cation electronegativity. Two areas of compound formation were identified for each of the fluorides. Magnesium and strontium fluorides are amphoteric compounds in terms of the Lewis acid and base theory. [ABSTRACT FROM AUTHOR]

Single crystals of Ba1 –x–yYbxRyF2 +x+y (R = Tm, Ho) solid solutions have been grown by the Bridgman technique in vacuum using a CF4 fluorination atmosphere. We have measured their thermal conductivity in the range 50–300 K and their refractive index from the visible to IR spectral region. As the ytterbium content increases from 2 to 14 mol %, the room-temperature thermal conductivity of the solid solutions with R = Tm and Ho decreases from 3.39 to 1.18 and from 3.11 to 1.18 W/(m K), respectively. Raising the holmium and thulium content of the solid solutions leads to a gradual increase in their refractive index, and it gradually decreases with increasing wavelength. [ABSTRACT FROM AUTHOR]

The luminescence of Er3+ ions in silica glasses synthesized by the direct sol–gel–glass transition method and by melting of activated gel grit using various precursors of optical centers was studied. The formation of complex centers including erbium, aluminum, and alkali metal ions was found to be one way of essentially increasing the half-width of the 4I13/2 → 4I15/2 luminescence band of these ions. [ABSTRACT FROM AUTHOR]

Single crystals of CaxSryBazF2 (x = 0.31–0.4045, y = 0.31–0.50, z = 0.10–0.38) and CaxSryBazYb0.005F2.005 (x = 0.295–0.495, y = 0.30–0.50, z = 0.10–0.40) fluorite solid solutions have been grown by the Bridgman technique, and their thermal conductivity has been measured in the range 50–300 K by an absolute steady-state axial heat flow technique. The room-temperature thermal conductivity of all the crystals studied is below 2.5 W/(m K). As the percentage of the heavy components of the solid solutions increases, their thermal conductivity decreases. In addition, this factor reduces the negative effect of the heterovalent dopant YbF3 on the thermal conductivity of the crystals. [ABSTRACT FROM AUTHOR]

The first study of some thermodynamic properties of a Cs2HfCl6 (CHC) scintillating crystal has been performed in a wide temperature range of 5–300 K. The CHC crystal exhibits a high thermal expansion coefficient (5.17 × 10−5 at 171 K), along with an extremely low heat conductivity (1.710 W m−1 K−1 at 50 K). A high heat capacity (1.22 J kg−1 K−1 at 3.8 K) along with a drastically low free mean path for phonons (about 26 Å) at temperatures around 50 K makes the CHC crystal unsuitable as a target material for cryogenic detectors. The results of the first operation of the CHC crystal as a cryogenic detector at sub-Kelvin temperatures clearly show the unfavorable phonon propagation properties of the material. On the other hand, the CHC crystal demonstrates excellent scintillating characteristics with a relatively high light yield under gamma irradiation (the detected signal is about 5200 photons per MeV). The refractive index within the (1.66–1.67) interval for light in visible and near-infrared spectral ranges was measured at room temperature. A cost- and time-effective approach for new crystalline material characterization as a target for cryogenic detectors based on the evaluation of the thermodynamic properties of the material is proposed. [ABSTRACT FROM AUTHOR]

Single crystals of Ca1 – ySryRхF2 +х (R = Ho, Pr) solid solutions with high optical quality have been grown by the Bridgman technique in vacuum using a fluorination atmosphere. The thermal conductivity of the Ca0.60Sr0.40 –хHoхF2 +х solid solutions decreases from 3.27 to 2.37 W/(m K) as the fraction of holmium rises from 0 to 3 mol %, respectively. The room-temperature thermal conductivity of the Ca0.50Sr0.50 –хPrхF2 +х solid solutions decreases from 3.38 to 2.18 W/(m K) as the fraction of praseodymium rises from 0 to 8 mol %, respectively. Increasing the holmium and praseodymium content of the ternary solid solutions leads to a gradual increase in their refractive index. With increasing wavelength, the refractive index gradually decreases. [ABSTRACT FROM AUTHOR]

The phase composition and structure of oxide and hydrogen-reduced iron–ruthenium systems are studied using conversion and adsorption Mössbauer spectroscopy, as well as X-ray diffraction methods. In samples with metal concentration (mass %) 50Fe–50Ru after calcination in air at 773 and 973 K, nanosystems containing two phases with different degrees of dispersion are formed (α-Fe2O3 with an admixture of Ru and RuO2 with an admixture of Fe, respectively). Structural transformations of the nanosystem calcinated at 973 K in different reduction conditions are investigated. It is shown that the formation of nanostructures depends on the initial and final reduction temperatures. The presence of ruthenium substantially changes the reduction kinetics of oxide systems. It is shown that upon an increase in the reduction temperature, the rearrangement of initial stoichiometric oxides to intermediate oxide structures with varying compositions and with different crystal lattice types is observed. The terminating stage of reduction is the formation of metal clusters or solid solutions of intermetallides. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of up-conversion luminescent composite films based on a nanocellulose matrix containing Sr1−xHoxF2+x particles was proposed. The combination of sulfuric acid hydrolysis and ultrasonication allowed us to synthesize a series of stable nanocellulose dispersions from various raw materials (powdered sulphate bleached wood pulp, Blue Ribbon filter paper, and microcrystalline cellulose Avicel). The size distribution of cellulose nanoparticles in the aqueous dispersions was determined. Cellulose nanocrystals (CNC) and/or cellulose nanofibrils (CNF) dispersions were used to fabricate thin films by solution casting followed by solvent evaporation under ambient conditions. The size and shape of cellulose nanoparticles, surface morphology, crystallinity index of nanocellulose, polymerization degree, and optical properties were studied. By mixing aqueous dispersions of CNC with up-conversion Sr1−xHoxF2+x particles, homogeneous suspensions were obtained. Finally, a solution casting technique was used to prepare CNC/Sr1−xHoxF2+x and CNC/CNF/Sr1−xHoxF2+x nanocomposite films. CNC/CNF dispersions were utilized for the production of flexible, durable, transparent composite films. The synthesized nanocomposites demonstrated intense red luminescence upon Ho3+ excitation by 1912 nm laser radiation. The obtained up-conversion luminescent composite films can be considered as a promising material for photonics, in particular for near-IR laser radiation visualization, luminescent labeling and luminescent sensorics.Graphical abstract: [ABSTRACT FROM AUTHOR]

Proceeding from the phase diagram of the CaF2-SrF2 system, the stability of crystal-melt interface of solid solution against constitutional supercooling has been calculated. When comparing the stability function F(x) calculated curve with the results of single crystals growing by the Bridgman method, the interdiffusion coefficient of cations in melt was estimated to be D > 2.4 × 10-4 cm2/s. [ABSTRACT FROM AUTHOR]

Polymer composites including modified multiwall carbon nanotubes were obtained by the block polymerisation of triethylene glycol dimethacrylate. The heat stability and microhardness of the materials were studied. A composite doped with nanotubes is more stable after annealing and hydrochloric acid treatment. [ABSTRACT FROM AUTHOR]

Single crystals of LiY1-xLuxF4 (x = 0, 0.25, 0.5, 0.65, 0.9) solid solution were grown by Bridgman-Stockbarger technique. Melting points determined by DSC monotonically varied with composition from 831 to 841 K when x increased. Interval between liquidus and solidus curves is not larger 1°C. This feature extremely favors to the growth of homogeneous single crystals from melt. Heat conductivity (κ) of solid solution is lower than that of LiYF4 and LiLuF4 components. In the region 0.25 ≤ x ≤ 0.65 at 300 K, κ = 4 ± 0.1 W/(m K). [ABSTRACT FROM AUTHOR]

Based on the analysis of the absorption spectra of Er-doped calcium-niobium-gallium garnet (Er:CNGG) crystals according to the Judd-Ofelt theory, the intensity parameters for these crystals are determined to be Θ2 = 3.43 × 10−20 cm2 Θ4 = 1.20 × 10−20 cm2, and Θ6 = 0.58 × 10−20 cm2. The parameters found are compared with the intensity parameters for other laser oxide crystals. Using these intensity parameters, the probabilities of radiative transitions between the energy levels of Er3+ ions in CNGG crystals and the luminescence branching ratios βJJ’ are calculated. From the measured lifetime of the 4 I 11/2 level of Er3+ ions (τ = 626 μs) and the probability of the radiative transition from this level ( A = 192 s−1), it is found that about 88% of the excitation energy in the Er:CNGG crystals is nonradiatively transferred from the 4 I 11/2 to the 4 I 13/2 level. It is suggested that an increase in the oscillator strength and in the line strength of the 4 I 15/2 → 2 H 11/2 transition of Er3+ in CNGG crystals, as well as an increase in the intensity parameter Θ2 with respect to the corresponding parameters for other garnet crystals are caused by the existence in CNGG crystals of Er3+ centers with the environment symmetry lower than D 2. [ABSTRACT FROM AUTHOR]