Roman Avetisov

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.

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.

To the homogeneity range of tris(8-hydroxyquinoline)gallium

A new technique for the analysis of p8-Hq–T diagrams has been developed for the metal–organic phosphor tris(8-hydroxyquinoline)gallium. The detection of mono- and bivariant equilibria within the p8-Hq–T diagram was done using simultaneous measurements of the photoluminescence and reflection spectra of the condensed phase under controlled p8-Hq pressure and temperature. Using preparations with purity better 99.9988 wt%, the Si-Gaq3Sj-Gaq3V and Si-Gaq3LV equilibria were studied and the corresponding p8-Hq–T diagram was plotted in the 408–665 K temperature range. For the α-Gaq3, it was demonstrated that changing the synthesis conditions within the homogeneity range of the phase resulted in change in the cell volume, chemical activity and electrical properties of crystalline preparation and thin layers deposited due to it.

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.

Synthesis condition influence on stability of metal-organic phosphor based on 8-hydroxyquinoline

Tris(8-hydroxyquinoline) aluminum (Alq₃) powders were synthesized under controlled 8-Hq partial pressure. It was shown that the P_8-Hq increase resulted to changes in the photoluminescence characteristics and the life-time of the Alq₃ phosphor.

Novel hybrid materials based on various oxyquinoline organic phosphour complexes and oxyfluoride glass

Novel luminescent organic-inorganic hybrid materials were synthesized by high temperature reaction between metalorganic phosphors and glass. In the present research we used a lead fluoroborate glass as an inorganic matrix and various luminescent oxyquinoline complexes as organic active agent.

Hybrid nanofilms with laser-control luminescence

Nanosize films of organic electroluminophors have offered the challenge to a new generation of light emitting devices - OLED. Tris-(8-oxyquinoline) aluminum (Alq3) was one of the first compounds which demonstrated high efficient green electroluminescence and to the moment it is still used as emission and electron transport material in OLED. Alq3 is known to exist in several polymorphs with photoluminescence (PL) maximum varied from 537 to 481 nm. One of main problem of OLED technology consists in a high cost of organic materials. An attempt to use organic-inorganic hybrid materials for a creation of a novel thin film emission device has not been very successful yet. But the investigation of hybrid material (HM) based on B2O3 glass matrix and Alq3 as phosphor agent showed that there were observed a significant shift of luminescent peak to short waves after bulk HM annealing. The change in the luminescence spectrum can was explained by the polymorph and/or conformation transitions in Alq3 in the crystal field of the matrix.