LUMINESCENCE OF CADMIUM SULFIDE QUANTUM DOTS IN FLUOROPHOSPHATE GLASSES

Cadmium sulfide quantum dots are perspective materials in optics, medicine, biology and optoelectronics. Fluorophosphate glasses, doped with cadmium sulfide quantum dots, were examined in the paper. Heat treatment led to the formation of quantum dots with diameters equal to 2.8 nm, 3.0 nm and 3.8 nm. In view of such changes in the quantum dots size the fundamental absorption edge shift and the luminescence band are being displaced to the long wavelengths. Luminescence lifetime has been found to be dependent on the registration wavelength in the range from 450 to 700 nm. Obtained fluorophosphate glasses with CdS quantum dots can find their application as fluorescent materials with intensive luminescence band and long excited-state natural lifetime

INTERACTION OF SILVER MOLECULAR CLUSTERS, INTRODUCED BY LOW-TEMPERATURE ION EXCHANGE METHOD, WITH NANOPARTICLES OF CdS IN FLUORINE PHOSPHATE GLASSES

Glasses with metallic and semi-conductive nano-particles appear to be perspective non-linear and luminescent materials of photonics. It was shown in theory that composite optical materials containing semi-conductive CdS-core with Ag shell (or vice versa) are optimal for enhancement of non-linear Kerr effect. Interaction of such an ensemble of particles leads to the forming of Ag island structures on the CdS particle, and formation of acanthite Ag2S on the two phases border (CdS-Ag) is minimal. In glasses synthesis of CdS quantum dots occurred due to thermal treatment close to glass transition temperature; introduction of silver was realized by low-temperature ion exchange (LIE). The main object of this work is investigation of Ag+ -LIE effect on the growth of CdS nano-particles. Two glasses were explored in this work: without CdS (glass 1) and with CdS (glass 2), processed by LIE at the temperature of 320°С for 10, 20 and 30 minutes and subsequent heat treatment at temperatures of 410°С and 420°С. In case of glass 1, intensive luminescence appears as a result of LIE, and subsequent heat treatment results in surface resonance at λ=410 nm. In case of glass 2, absorbance spectra change appears that is specific for formation of acanthite and weak luminescence shifting to long-wavelength region (from 550 to 700 nm) as a result of applying LIE and heat treatment. It indicates the growth of CdS quantum dots. Experiment has shown that quantum efficiency increases to 70% for glass 2 containing CdS quantum dots without LIE, while glass that contains silver shows steep decrease of quantum efficiency to 0%. That decrease is caused by formation of acanthite Ag2S on the surface of CdS quantum dot

STUDY OF STRONG CONFINEMENT OF CADMIUM SELENIDE QUANTUM DOTS IN FLUORINE-PHOSPHATE GLASSES

Fluorine-phosphate glasses doped with CdSe quantum dots were studied. As a result of glasses secondary heat-treatment, quantum dots were synthesized with sizes equal to 1.2-4.5 nm. Strong confinement was studied in two energy transitions (excited states of quantum dots) on photoluminescence excitation spectra. Experimental dependencies for the first and second energy transition on the nanoparticles size enable to conclude that no interaction occurs with fluorine-phosphate glass matrix and quantum dots

Yeast homologues of lethal giant larvae and type V myosin cooperate in the regulation of Rab-dependent vesicle clustering and polarized exocytosis

The yeast type V myosin, Myo2, and the lethal giant larvae homologue, Sro7, are important players in polarized exocytosis. This paper article characterizes the role of Myo2 both in recruiting Sro7 to sites of polarized growth and in negatively regulating a Sec4-dependent vesicle-clustering activity of Sro7

Cyclic Guanidines as Efficient Organocatalysts for the Synthesis of Polyurethanes

A systematic survey of basic/nucleophilic organocatalysts for the polyaddition in bulk of polyols, PEG-600, and PTMO-650, to isophorone diisocyanate (IPDI) has been performed. Guanidines were shown to be very efficient catalysts for the urethane linkage formation. Bicyclic penta-alkylated guanidines such as MTBD led to polyurethane molecular weight and dispersity that are in the range of those observed with tin-based catalysts such as DBTDL. Tetra-alkylated guanidine such as TBD was shown to be a weaker catalyst as compared to pentaalkylated guanidines, as a result of its high reactivity toward isocyanate, resulting in the formation of a less nucleophilic urea. Although the mechanism has not yet been firmly established, these experiments suggest that a nucleophilic-catalysis mechanism, involving the attack of one of the nitrogen of the guanidine onto the unsaturated system of the isocyanate, should not be totally ruled out with such strong Bronsted base catalysts