A. V. Khomyakov

Thermodynamic features of axial vibrational control technique for crystal growth from the melt

Direct measurements of crystallization heat of NaNO3 and CdTe melts activated by low-frequency vibrations by oscillating an inert baffle submerged into the melt demonstrated up to 30% increase compared to the regular melt. At a stationary state the crystallization heat increase depends on vibrational amplitude and frequency. The study of melt structure by Raman spectroscopy proved the assumption about the changing of component composition followed by its restructure under AVC processing. Kinetics of melt reconstruction depending on temperature and vibrational intensity was examined.

Non-stoichiometry of tris(8-hydroxyquinoline) aluminium: is it possible?

The dependence of the 8-hydroxyquinoline (8-Hq) vapor pressure on temperature, logP8-Hq [Torr] = 8.4249 − 2963.5/T, was experimentally determined in the 386–482 K temperature range using the Bourdon manometer technique. Tris(8-hydroxyquinoline) aluminum (α-Alq3) crystals were synthesized under the 8-Hq controlled partial pressure of 0.1–11.30 Torr. The influence of 8-Hq vapor pressure on the structural and luminescence characteristics of crystalline Alq3 was examined. It was found out that the P8-Hq increase resulted in the changes in the photoluminescence spectra maximum, decay kinetics, and structural characteristics. The unit cell volume of the α-Alq3 crystals decreased from 1141.1 to 1138.7 A3 upon P8-Hq increase.

Homogeneity limits and nonstoichiometry of vapor grown ZnTe and CdTe crystals

The homogeneity regions of zinc telluride ZnTe and cadmium telluride CdTe were studied by the “extraction” technique at 750–1365 K temperature range. It is shown that the homogeneity region of undoped ZnTe contains a stoichiometric composition. The existence of wurtzite-based ZnTe at high temperatures was proven and its lattice parameters were determined. A scheme of the 3C–2H polymorphous transition for ZnTe compounds is proposed in which the transition is followed by peritectic reactions at both the Te-rich and Zn-rich sides. In the case of CdTe, the solidus line near the melting point demonstrated an anomalous behavior, which could be explained in terms of the high-temperature polymorphous transition, but the polymorph was not fixed because of the low transition energy. The undoped ZnTe and CdTe single crystals were obtained by the Markov–Davydov vapor growth technique under pressures close to congruent sublimation conditions in the temperature range 1170–1320 K. The nonstoichiometry and impurity distribution in 60 mm diameter ZnTe and 100 mm diameter CdTe vapor grown crystals were examined.

Lead−barium fluoroborate glass ceramics doped with Nd3+ or Er3+

Lead−barium fluoroborate glasses in the PbF2–BaF2–B2O3, PbF2–BaO–B2O3, and PbO– BaF2–B2O3 systems doped with rare-earth ions (Nd3+ or Er3+) are synthesized and studied. It is shown that, based on these glasses, it is possible to produce transparent glass ceramics with fluoride crystalline phases, including ceramics with one crystalline phase of the fluorite structure. The spectral and luminescent properties of the doped glasses, glass ceramics, and polycrystalline complex fluorides containing Pb, Ba, and rare ions are studied.

New hybrid materials for organic light-emitting diode devices

The regularities of polymorphism in high-purity crystalline tris(8-hydroxyquinoline) aluminum, gallium, and indium (Meq3) have been studied in the temperature range of 300–712 K. From the results of an analysis of photoluminescence and Raman spectra and X-ray diffraction data, a generalized picture has been produced, according to which, for all the studied compounds, a series of polymorphic transitions is the same: β → α → δ → γ → ɛ. Based on high-purity single-phase specimens of the investigated metal complexes and boron oxide, new hybrid materials have been synthesized: bulk samples (alloying technique) and thin films (vacuum thermal evaporation). The photo- and electroluminescent properties of the hybrid materials at room temperature have been investigated. It has been established that, as the synthesis duration of the bulk hybrid materials increases from 5 to 60 min, a photoluminescence maximum shifts to a short-wavelength domain from the value typical of pure δ(γ)-Meq3 by 40, 15, and 10 nm for Alq3, Gaq3, and Inq3, respectively.

Hybrid materials based on organic luminophores in inorganic glass matrix

Hybrid materials were synthesized based on borate glass matrix and the tris(8-hydroxyquinoline) aluminum (Alq3) organic luminophore, which is used as a green luminophore in OLED devices. The luminescent properties of hybrid materials with 0.02–0.1 wt % of Alq3 in glass were studied. The luminescence peak of the hybrid material is significantly shifted to shorter wavelengths (443 nm versus 518 nm in pure Alq3 powder).

The influence of synthesis conditions on the stability of tris(8-hydroxyquinoline) aluminum organometallic luminophore

Single-phase crystalline luminophore tris(8-hydroxyquinoline) aluminum (Alq3) has been synthesized at Т = 483 K and a partial pressure of 8-hydroxyquinoline vapor from 0.15 to 6.12 Torr. The influence of P8-Hq on the luminescent characteristics of crystalline Alq3 samples has been studied. It has been found that an increase in P8-Hq led to a shift of the photoluminescence-band maximum and to a change in the photoluminescence-decay kinetics. It has been shown that Alq3 synthesized at Т = 483 K and P8-Hq = 6.12 Torr had the most stable spectral-luminescent characteristics. The results obtained are discussed taking into account defect formation in crystalline Alq3.

Purity of MoO3 from different manufacturers

Inductively coupled plasma mass spectrometry with the use of a reaction cell in collision mode has been used to determine the concentrations of 68 elemental impurities in six commercially available molybdenum( VI) oxide reagents. The results indicate that the purity of the reagents is not better than 3N (99.9 wt %). A major impurity in the MoO3 samples is tungsten. Its concentration ranges from 5 × 10–3 to 6 × 10–2 wt %, depending on the manufacturer.

Growth of Li2MoO4 Crystals from Activated Water Solutions

The possibility of obtaining lithium molybdate Li2MoO4 crystals from water solutions activated by low-frequency oscillations of a chemically inert body is examined. It is shown that the activation of the solution increases the equilibrium solubility of Li2MoO4 in the water solution in the temperature interval 25 – 28°C. It is found that the activation of a solution affects the form of the faceting of the crystals grown and the surface morphology of the faces. It is shown that activation of the solution decreases the inclusions of water in the crystals and improves the surface quality of the growing crystal.

Deep Tellurium Purification for the Production of Electronic and Photonic Materials

Abstractcarry out the process of obtaining high-purity tellurium by the vacuum distillation method, a reactor design consisting of high-purity quartz glass and graphite is proposed. During the process, the tellurium melt evaporates; and the vapor is transferred from the hot part of the system to the colder one and condenses in the form of a solid phase (distillate) without the formation of a liquid. Regularities in the redistribution of impurities between the distillate and the cube stillage residue, as well as the spatial distribution of impurities in the distillate during the purification of metallic tellurium, are studied. It is established that some impurities, for example, s-metals, Zn, Ni, and V, and rare metals, are distributed uniformly along the length (20 cm) of the distillate. At the same time, Se tends to concentrate in the far (from the still) part of the distillate with a difference of more than one order of magnitude than in the near part.