Influence of the rate of increase in the induction on the spectral characteristics of luminescence of ZnS: Mn under treatment in a magnetic field

This paper reports on the results of the investigation of photoluminescence and luminescence excitation spectra of a ZnS powder thermally doped with MnCl · 4H₂O or MnS and subjected to a series of treatments in a pulsed magnetic field with the same maximum amplitude of the magnetic field induction (B _max = 0.3 T) but with different rates of its increase $ \dot B $ \dot B (t) to a maximum value. It has been revealed that pulsed magnetic fields with different rates of increase in the induction B nonlinearly affect the spectral characteristics of the ZnS: Mn compounds. The processes occurring in the material, which can lead to a change in its spectral characteristics due to the manifestation of the magnetoplastic effect, and the influence of the parameter $ \dot B $ \dot B (t) of the magnetic field on the efficiency of the external action have been discussed. It has been demonstrated that a variation in the parameter $ \dot B $ \dot B (t) makes it possible to control the location of defects in the nearest environment of Mn²⁺ ions in the ZnS compound after the completion of treatment of the material in a magnetic field. The mechanisms responsible for the different effects exerted by energetically identical external disturbances on the system have been proposed.     

Concerning the measurement of the radiation energy density distribution over the beam cross section of a commercial laser

The operating principle and the construction are considered of a photodiode matrix system intended for the investigation of the radiation-density distribution over the cross section of a laser beam.Translated from Voprosy Metrologicheskogo Obespecheniya Izmereniya Parametrov Tekhnologicheskikh Lazerov, pp. 29–36, 1984.     

Effect of the order in which powdered ZnS is doped with copper chloride and indium on formation of luminescence centers

We consider the effect of the order in which In and CuCl impurities are added during thermal doping on the luminescence characteristics of ZnS, and also their role in formation of emission centers in zinc sulfide. We show that the order in which the impurities (acting as activators or coactivators) are added to the ZnS plays the determining role in formation of the spectral characteristics of the luminophore obtained. We have established that adding indium first during thermal doping of zinc sulfide with In and CuCl prevents diffusion of Cu into the interior of the ZnS. Adding indium after CuCl or adding indium simultaneously with CuCl prevents formation of the Cu2S and CuS phases or promotes degradation of the indicated phases in ZnS. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 601–605, September–October, 2006.     

Conformation of 4,5,6-substituted 2-isopropyl-1,3,2-oxathioborinanes

The configuration and predominant conformations of 2-isopropyl-4,5,6-alkylsubstituted 1,3,2-oxathioborinanes have been studied by ¹H-NMR spectroscopy. 2,4-and 2,6-Dialkylsubstituted derivatives exist in near half-chair conformations, while 6,6-dimethyl-2-isopropyl-1,3,2-oxathioborinane exists in two energetically equivalent inverting forms. 2,5,6- and 2,4,6-Trialkylsubstituted 1,3,2-oxathioborinanes consist of mixtures of stereoisomers differing in the orientations of the alkyl groups at the C₍₆₎ and C₍₄₎ ring atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 242–245, February, 1990.     

Preferred Conformations of Calix[4]- and Calix[6]arenes,Calculated ab initio

Ab initio STO-2G calculations showed that the preferred conformation of a series of calix[6]arenes substituted at the upper rim is a compressed cone stabilized by a pseudo-ring of six hydrogen bonds with close characteristics. The endocyclic dihedral angles between the benzene ring planes, characterizing the molecular shape of the above macrocyclic compounds in this conformation, were calculated. The calculation results are consistent with the conformational data obtained by other theoretical methods and describe the characteristics of hydrogen bonds more adequately, in agreement with the experimental data and with the existing concepts of the hydrogen bonding efficiency.     

Conformational Analysis of p-Substituted Calix[6]arenes by Molecular Mechanics and Quantum-Chemical Methods

The molecular mechanics (AMBER 3.0) and quantum-chemical (AM1) calculations indicated that in the series of calix[6]arenes substituted on the upper rim, the preferable conformation is a pinched cone stabilized by the nonequivalent hydrogen bonds on the lower rim of the macrocycle molecule. For the basic conformers of the macrocycles under study, the endocyclic dihedral angles between the planes of the benzene rings characterizing the shape of the macrocycles were calculated. The results of AM1 and AMBER 3.0 calculations agree with the results of the conformational analysis of calix[6]arene molecules by experimental and theoretical methods.     

Effect of microwave annealing on silicon dioxide/silicon carbide structures

The methods of atomic force microscopy and optical absorption spectroscopy are applied to study the effect of microwave treatment on the properties of SiO₂/SiC structures obtained by rapid thermal annealing and conventional thermal oxidation in steam. From the variation of the sample optical density with total time of microwave treatment, it is concluded that the structures prepared by rapid thermal annealing are more stable against microwave radiation. It is shown that long-term microwave treatment flattens the oxide film surface at the nanolevel regardless of the method of silicon carbide oxidation.     

Ab initio and density functional studies of cooperative hydrogen bonding in calix[4]-and calix[6]arenes

The cone conformation of C ₄ symmetry is shown by the Hartree-Fock method (3-21G basis) to be the predominant conformer of calix[4]arene; the compressed cone of C ₂ symmetry is the major conformer of calix[6]arene. Using quantum chemical methods we calculated hydrogen bond cleavage energies for calix[4]-(ab initio and density functional methods) and calix[6]arene (ab initio), and also for the complex of calix[4]arene with carbon disulfide. These energies along with structural data point to the cooperative effect of hydrogen bonds. The results of these studies provided an explanation to the greater conformational lability of calix[6]arene compared with calix[4]arene molecules. It is also predicted that the nucleophilic substitution reaction involving calix[6]arene in the presence of weak bases and in aprotic solvents, as well as in the gas phase, will occur via diastereomeric transition states.     

Formation of titanium oxide films on the surface of porous silicon carbide

The influence of rapid thermal annealing (RTA) on the properties of a titanium film on the surface of porous silicon carbide is considered. It is shown that an increase in the RTA temperature to 900°C stabilizes the phase composition of the forming titanium oxide over the film, which is identified as rutile. Due to the formation of titanium oxide nanoclusters under the action of RTA, an additional photoluminescence band arises near 2.5 eV. Based on Auger spectrometry data, a multilayer model to calculate the optical parameters of titanium oxide films covering porous silicon carbide is suggested.