Background. In modern production of power electronic devices for lowtemperature connection of their structural and functional elements, sintering technology is widely used with the use of special pastes of foreign manufacturers based on ultrafine silver powders. The purpose of the work was to develop a domestic silver-containing paste for low-temperature connection of structural elements of power semiconductor devices. Materials and methods. Domestic ultrafine silver powder with modified granulometric composition was used as a filler in the developed paste. Organic components were introduced into the composition of the developed paste, including myristic acid as a dispersant, as well as alpha-terpineol and nonanol-1, allowing to regulate the rheological properties of the paste. Thermoanalytical characteristics of the developed paste and organic components included in its composition were determined using Netszch TG 209 F1 Libra and Netszch DSC 404 F1 Pegasus devices. Adhesion characteristics of sintered layers of the studied silvercontaining pastes were measured by the L-peeling method on a SHIMADZU AG 100 KNX testing machine using additional equipment. Results. Thermogravimetric characteristics of higher carboxylic acids with the number of carbon atoms from C10 to C18 – possible organic dispersants of the developed silver-containing paste – were studied. Myristic acid (C14) was chosen as the most optimal particle dispersant. Organic substances allowing to regulate the rheological properties of the created paste (alpha-terpineol and nonanol-1) were selected and their thermogravimetric characteristics were studied. A technology for preparing a silver-containing paste has been developed, paste samples have been manufactured, their thermo-analytical characteristics have been studied and compared with the measured similar characteristics of ASP-043 (Heraeus) paste. A difference in the composition of the organic component of the developed paste from that of a foreign manufacturer has been established. The adhesion strength of sintered layers of silver-containing pastes has been measured using the L-peeling method. It has been established that the adhesive strength of the developed domestic silver-containing paste, taking into account the experimental error, is close to the adhesive strength of the imported ASP-043 (Heraeus) paste. Conclusions. A domestic silver-containing paste has been developed for low-temperature bonding of structural and functional elements of power semiconductor devices with adhesive characteristics close to the corresponding values of the imported ASP-043 (Heraeus) paste.

Wereport on the dynamics of laser generation during the transition from stable mode-locking to mode-locking accompanied by long period pulsations. In this case, the optical spectrum in the long-period pulsation regime is accompanied by emission in three spectral regions with maximum at three wavelengths: 1562, 1598 and 1623 nm.

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.

Thin dielectric Al2O3 and SrO films obtained by thermal evaporation in vacuum, as well as Si3N4 and SiO2 films obtained by RF magnetron sputtering, were studied by atomic force microscopy. The metric and fractal parameters of dielectric layers are estimated using the Gwyddion graphical program for analyzing data from scanning probe microscopy. It has been established that the maximum values of the fractal dimension are characteristic of aluminum oxide films with a thickness of 0.5 μm, while the smallest root-mean-square roughness is characteristic of strontium oxide films. The prospects for using the analyzed dielectric films as insulating layer of sensitive elements of strain gauge pressure sensors with a conductive elastic element are demonstrated.

The polarization properties of bismuth active centers (BACs) are important for many applications of bismuth-doped fibers, but they are still lacking in study. In this paper, we present the measurements of polarized luminescence (PL) of the BACs formed in a Bi-doped phosphosilicate glass matrix. This research was performed on phosphosilicate fiber preforms used for the drawing of active bismuth-doped fibers for efficient optical amplifiers and lasers. The degree of polarization (DOP) of luminescence of the BACs associated with phosphorus and silica (BAC-P and BAC-Si) is provided and discussed. The DOP of luminescence at the 1320 nm wavelength appeared to be around 19%, 0% and 7.5% for pumps at 1240 nm, 762 nm and 425 nm, respectively. The DOP of PL caused by resonant excitation may be described in terms of a model of a partially anisotropic oscillator with the parameters represented by the principal axes of an ellipsoid. For the resonant excitation at 1240 nm, the ratio of the major principal axis to the minor one turned out to be 5.1 and 3.0 for BAC-P and BAC-Si, respectively.

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.

In this work, we study the effects of treating nanostructured SnO2–SiO2 films derived by a sol-gel method with nitrogen and oxygen plasma. The structural and chemical properties of the films are closely investigated. To quantify surface site activity in the films following treatment, we employed a photocatalytic UV degradation test with brilliant green. Using X-ray photoelectron spectroscopy, it was found that treatment with oxygen plasma led to a high deviation in the stoichiometry of the SnO2 surface and even the appearance of a tin monoxide phase. These samples also exhibited a maximum photocatalytic activity. In contrast, treatment with nitrogen plasma did not lead to any noticeable changes in the material. However, increasing the power of the plasma source from 250 W to 500 W led to the appearance of an SnO fraction on the surface and a reduction in the photocatalytic activity. In general, all the types of plasma treatment tested led to amorphization in the SnO2–SiO2 samples.

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 .

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.

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

— 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.

The crystal structure of anhydrous sodium sulfate purified by double recrystallization from an aqueous solution was investigated by thermal analysis and X-ray phase analysis in the temperature range from 25°C to 300°C. When heated at a rate of 2–5 K/min, Na2SO4 undergoes a first-order phase transition (onset at 240°C) from an orthorhombic structure (space group Fddd, phase V) to a hexagonal structure (space group P63/mmc, phase I). However, lines of orthorhombic phase III (space group Cmcm) appear on the X-ray pattern at 225°C; phase III coexists with phases V and I at 240°C.