Band-edge photoluminescence in nanocrystalline ZnO:In films prepared by electrostatic spray deposition

ZnO:In films are successfully prepared by using the electrostatic spray deposition technique. X-ray diffraction indicates that the ZnO:In films have a polycrystalline hexagonal wurtzite structure with lattice parameters a=3.267 Å and c=5.209 Å. Photoluminescence properties of the films are investigated in the temperature range of 11.6-300 K, showing strong luminescence in the whole range of temperature. The temperature dependence of the photoluminescence are carried out with full profile fitting of spectra, which clearly shows that the ultraviolet (UV) emission in In-doped ZnO films at low temperature are attributed to emission of a neutral donor-bound exciton (D^°X) and recombination of donor-acceptor pairs (DAP), while the UV emission at room temperature originates from radiative transition of an electron bound on a donor to the valence band.     

Spectral manifestations of hybrid association of CdS colloidal quantum dots with methylene blue molecules

We have studied the spectral properties of mixtures formed by CdS colloidal quantum dots with an average diameter of 2.5 nm and methylene blue molecules and that are dispersed into gelatin. We have revealed that, in the presence of CdS quantum dots, the luminescence intensity of methylene blue increases. We suggest a model of this effect, which is based on electronic excitation energy transfer from luminescence centers of CdS quantum dots to methylene blue molecules.     

Confined-acoustic-phonon-assisted cyclotron resonance via multi-photon absorption process in GaAs quantum well structure

Phonon-assisted cyclotron resonance (PACR) in GaAs quantum well (QW) structure is investigated via multi-photon absorption process when electrons interact with the confined acoustic phonon through deformation potential. The additional peaks in the absorption spectrum due to transitions between Landau levels accompanied with the emission and absorption of phonons are indicated. The dependence of absorption power on the temperature, magnetic field and well width is presented. Using profile method, we obtain PACR-linewidth as profiles of the curves. The temperature, magnetic field and well width dependences of the PACR-linewidth are investigated. The results are compared with those in the case of mono-photon absorption process, as well as in the electron-bulk acoustic phonon interaction. The results show that the multi-photon absorption process is strong enough to be detected in PACR.     

Use of nuclear magnetic resonance and gas-liquid chromatography for the study of microbial nitrile-hydratases and amidases

Some microbial strains can hydrolyse many nitriles to the corresponding organic acids by means of two enzymes: a nitrile-hydratase which hydrates the nitrile to the corresponding amide, and an amidase which hydrolyses the amide to the corresponding acid. Two methods are proposed for the assay of the enzymatic activities: proton magnetic resonance spectrometry (n.m.r.) and gas-liquid chromatography (g.l.c.). For the assay of these enzymatic activities (nitrile-hydratase and amidase), g.l.c, was better, because it was more precise and much more sensitive than the n.m.r, method. The examples of acetonitrile and acetamide are described in detail.     

Uncatalyzed insertion reaction of isocyanides into a carbon-sulfur bond

Tert-butylisocyanide and tert-octylisocyanide insert into the carbone-sulfur bond of activated sulfides 2 yielding thioimidates 5 which rearrange to enamines 6.     

On-line separation of short-lived tungsten isotopes from tantalum,hafnium and lutetium by adsorption on ion exchangers from aqueous ammonia solution

The title goal was achieved using a DOWEX 50Wx8 cation exchange column saturated with La(OH)₃ and ammonia solution as eluent. Hf, Ta and Lu were adsorbed on this column, whereas W remained in the solution. This chemical system may be used for fast on-line separations of element 106.     

Optical and chromaticity characteristics of cobalt 1-nitroso-2-naphthol-3,6-disulfonates

The optimum conditions of the complexation of cobalt with nitroso-R salt in the presence of and without ascorbic acid were found. Molar coefficients of chromaticity functions of the complexes were calculated, and it was demonstrated that cobalt(II) and cobalt(III) complexes can be distinguished only with the use of chromaticity functions, whereas their optical characteristics are nearly the same. For practical purposes, it is better to introduce ascorbic acid and to obtain the kinetically inert complex of cobalt(III) with nitroso-R salt.     

On the Basicity of Triarylmethylamines in Solution

The pK of 11 triarylmethylamines (tritylamines), eight of which are new, and some related bases were measured in methylcellosolve/water 80:20 (MCS); some were also measured in dioxane/water 60:40 (Dx), acetonitrile (An), nitrobenzene (Nb) and acetic acid (Ac). (1) The influence of the aryl groups on the basicity is essentially additive; (2) In different solvents, similar linear free energy relationships were found, with differences in p* characteristic of solvation; (3) The influence on basicity of substituents of the aryl groups follows Hammett's relationship. These results indicate a preponderance of inductive effects. N, N-Dimethyltritylamine (3b) (pK=3.40) shows a marked crowding effect, absent in the isomeric tertiary amines 13 and 14 . Tri-p-nitrotritylamine (10a) (pK=3.10), N, N-dimethyl-tri-p-nitrotritylamine (10b) (pK=0.50), and 3b are particularly weak bases; the base-weakening effect of the trinitrotrityl group is similar to that of the cyanomethyl and trifluoroethyl groups.