The PbO–Ga2O3 glass-forming system with a lead oxide content of more than 50 mol.

Glasses in the $\mathrm{PbCl}_{2}-\mathrm{TeO}_{2}$ system were synthesized from high-purity starting materials. The glasses have record low absorption of hydroxyl groups, wide range of transparency and good crystallization stability. The materials are promising for drawing optical fibers.

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.

New oxychloride lead borate glasses in the xPbCl2–(50-0.5x)PbO–(50-0.5x)B2O3 system were synthesized with a maximum lead chloride content of 40 mol%. The characteristic temperatures and mechanical and optical properties were studied. The incorporation of lead chloride led to a significant expansion of the transparency range in the UV (up to 355 nm) and IR regions (up to 4710 nm). Decreases in the Vickers hardness, density, and glass transition temperature were the consequences of a change in the structure. The studied glasses are promising materials for photonics and IR optics. The structure of the PbCl2–PbO–B2O3 system was analyzed in detail using vibrational spectroscopy and X-ray diffraction.

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.

Методом Бриджмена выращены монокристаллические образцы твердых растворов Ca x Sr y Ba z F 2 ( x = 0.31–0.4045, y = 0.31–0.50, z = 0.10–0.38) и Ca x Sr y Ba z Yb 0.005 F 2.005 ( x = 0.295–0.495, y = 0.30–0.50, z = 0.10–0.40) с флюоритовой структурой. Абсолютным стационарным методом продольного теплового потока в интервале 50–300 K исследована их теплопроводность. При комнатной температуре значения коэффициента теплопроводности всех исследованных образцов ниже 2.5 Вт/(м К). Теплопроводность убывает с увеличением содержания тяжелых компонентов в данных твердых растворах. Этот же фактор снижает негативное влияние на теплопроводность добавки гетеровалентной примеси YbF 3 .

— Single crystals of Ca x Sr y Ba z F 2 ( x = 0.31–0.4045, y = 0.31–0.50, z = 0.10–0.38) and Ca x Sr y Ba z Yb 0.005 F 2.005 ( 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 YbF 3 on the thermal conductivity of the crystals.

Bismuth-germanate glasses, which are well known as a promising active medium for broadband near-infrared spectral range fiber lasers and as an initial matrix for nonlinear optical glass ceramics, have been synthesized in a 5–50 mol% Bi2O3 wide concentration range. Their structural and physical characteristics were studied by Raman and FT-IR spectroscopy, differential scanning calorimetry, X-ray diffraction, optical, and luminescence methods. It has been found that the main structural units of glasses are [BiO6] and [GeO4]. The growth in bismuth oxide content resulted in an increase in density and refractive index. The spectral and luminescent properties of glasses strongly depended on the amount of bismuth active centers. The maximum intensity of IR luminescence has been achieved for the 5Bi2O3-95GeO2 sample. The heat treatment of glasses resulted in the formation of several crystalline phases, the structure and amount of which depended on the initial glass composition. The main phases were non-linear Bi2GeO5 and scintillating Bi4Ge3O12. Comparing with the previous papers dealing with bismuth and germanium oxide-based glasses, we enlarge the range of Bi2O3 concentration up to 50 mol% and decrease the synthesis temperature from 1300 to 1100 °C.

The optical characteristics of Ca0.33Sr0.33Ba0.33F2 (CSBF) single crystal of a ternary solid solution of calcium, strontium and barium fluorides were studied in order to create disordered optical media. Characteristics of the single crystals of individual fluorides CaF2, SrF2, BaF2 and binary solid solutions Ca0.6Sr0.4F2 and Ba0.67Sr0.33F2 were obtained. Broadband reflection and transmission spectra of the said crystals were recorded in the frequency range of 3-5000 cm(-1), and the values of the complex refractive indexes and dielectric constants were calculated. The generalized four parameter model were used for calculation of absorption band parameters. For the CSBF crystal, a significant broadening of the band was observed in the absorption region at optical phonon modes along with an increased absorption in the region below the optical phonon frequencies, which is typical for disordered dielectric media.

Samples of CaF2:D y 3+ crystals and CaF2-SrF2:D y 3+ solid solution were obtained by the Bridgman-Stockbarger method. The spectroscopic characteristics were calculated from the experimentally obtained optical spectra. Using the Judd-Ofelt analysis, intensity parameters 02,4,6 were obtained. On their basis, integral luminescence cross sections, radiative lifetimes, and luminescence branching coefficients in the IR region are calculated. Using the correspondence method, the luminescence spectra of the 6H13/2 -> 6H15/2 transition were obtained

Using the Bridgman-Stockbarger method, crystals of triple fluoride CaF2-SrF2-BaF2 were grown in a composition range similar to that of CaSrBaF6. The crystals were 10-12 mm in diameter and 50–60 mm in length. The CaSrBaF6 crystal is a new optical material which is transparent in the mid-IR, visible and UV ranges. The uneven distribution of the components along the length of the crystal did not exceed 10 %. The edge of the absorption band in the IR range was 14.3 μm, and the optical absorption at the wavelength of 200 nm did not exceed 18 % (less than 0.2 cm–1). The refraction indices were 1.4527, 1.4488, and 1.4458 for the wavelengths of 633, 969, and 1539 nm respectively. The crystal melts in the temperature range of 1150–1210 °С. The CaSrBaF6 composition is an appropriate matrix for doping with rare-earth ions in order to obtain functional single-crystal and ceramic materials of the visible and IR ranges.

A concentration series of Ca(1 − X)SrXF2:4 mol % YbF3 crystals with Х varying from 0 to 1 has been grown. The absorption spectra of Yb3+ ions in these crystals are measured at temperatures of 300 and 77 K. It is shown that the intensity ratio of the absorption lines of clusters and tetragonal centers in the congruent crystals is higher than that in the other CaF2–SrF2 solid solution crystals. Analysis of the absorption profiles of Yb3+ optical centers in the concentration series of the solid solution crystals shows that it is energetically favorable for the Sr2+ ion to enter the local environment of both the tetragonal center and the cluster.

Выращена концентрационная серия кристаллов Ca(1-X)SrXF2 : 4 mol.% YbF3 при варьировании X от 0 до 1. Исследованы спектры поглощения ионов Yb3+ в этих кристаллах при температурах 300 и 77 K. Показано, что для кристаллов конгруэнтного состава характерна большая интенсивность линий поглощения кластеров относительно линии поглощения тетрагональных центров по сравнению с другими кристаллами твердого раствора CaF2-SrF2. Из анализа контуров линий поглощения оптических центров ионов Yb3+ в образцах концентрационной серии кристаллов твердых растворов следует, что ионам Sr2+ энергетически выгодно находиться в ближайшем локальном окружении как тетрагонального центра, так и кластера. Ключевые слова: кристаллы фторидов, твердые растворы, оптическая спектроскопия, иттербий, кластеры, неоднородное уширение.

X-ray diffraction studies of crystals CaF 2 -ErF 3 , CaF 2 -YbF 3 , Ca x Sr 1-x F 2 were carried out at various concentrations of rare-earth elements. Phase analysis performed by the data base PDF-2. The structural characteristics of the found phases were refined using the full-profile analysis (Rietveld method). The dependence of the lattice constant on the impurity concentration is revealed.

The absorption spectra of Yb 3+ ions in a concentration series of Ca( 1-X ) Sr X F 2 crystals: 4 mol% YbF 3 were studied with varying X from 0 to 1 at temperatures T=300K and T=77K. The largest peak absorption cross section for the optical centers of Yb 3+ ion clusters is characteristic of congruently melting crystals. The composition regions of CaF 2 -SrF 2 -4 mol.% YbF 3 crystals with the maximum inhomogeneous broadening of spectral lines were determined. The features of the effect of the composition on the dominant optical centers of Yb 3+ ions are revealed.

The glasses in PbF2-B2O3.REF3 (RE = Nd, Nd + La, Nd + Lu) system have been synthesized. The initial glasses were doped with several RE's (0.2-3.0 at%), one of which had no luminescent f-f transitions (La, Lu) and performed only the function of the stabilizer of the cubic phase PbF2, and the other (Nd) played the role of a luminescence center. Glass-ceramics have been obtained by the controlled crystallization of glasses with formation of Pb1-xLa/NdxF2-x or Pb1-xLu/Nd(3)F(2+)3 solid solutions. The luminescence spectra of co-activated glassceramics as well as crystalline samples demonstrated a splitting of the "0-0" line for the F-4(3/2) -> I-4(9/2) transition. It has been shown that it is possible to stabilize a cubic phase based on PbF2 by several RE co-doping and to obtain glass-ceramics with a crystalline phase in which the concentration quenching was reduced compared to glassceramics doped with a single activator.

The phase diagram of the NaF-SrF2 system was studied by thermal analysis and X-ray powder diffraction analysis with the determination of the chemical composition. The system was found to be of the eutectic type. The eutectic co-ordinates are 853 degrees C, 32 mol % SrF2. A narrow range of the existence of solid solution Sr1-xNaxF2-x was established. The NaF solubility reaches a maximal value of x = 0.035 at eutectic temperature. The solubility of KF in SrF2 is very low.

The phase diagram of the NaF–CaF 2 system was studied by thermal analysis and X-ray powder diffraction analysis with the determination of the chemical composition. The system was found to be of the eutectic type. A narrow range of the existence of solid solution Ca 1–x Na x F 2–x was established. The NaF solubility reaches a maximal value of x = 0.035 at 1200 ± 50°C (the temperature at which there is a diffuse phase transition in fluorite). At 920 ± 25°C, the NaF solubility reaches a minimum (<0.4 mol %) and increases again to 2.2 ± 0.2 mol % at a eutectic temperature (818°C). The ionic conductivity increases by three orders of magnitude after adding NaF to CaF 2 .