Mechanism of infrared stimulation and quenching in ZnS: Cu,Al Phosphors

To investigate the mechanism of the stimulation and quenching of the green luminescence in ZnS: Cu, Al phosphors by infrared (IR) light of 0.7–1.5 μm, stimulation and quenching spectra, IR effects on time-resolved emission spectra, and IR-induced photoconductivity are measured at 4.2 K, 77 K, and room temperature. Both the stimulation and quenching are caused by the IR transitions ascribed to excited copper acceptors. It is concluded that the stimulation is induced by the process in which holes produced by IR light migrate among copper acceptors, so that the statistical distribution of the intrapair separations of excited copper-aluminum pairs are changed to shorter distances. It is found that at low temperatures the holes migrate from one copper acceptor to another without being thermally released to the valence band. It is confirmed that the quenching is caused by the recombination of holes released to the valence band with electrons in the conduction band via some kind of nonradiative recombination centers.     

Preparation of polysiloxanes from silicic acid. V. Condensation of silicic acid butyl esters and formation of silica fiber from the ester solutions

The condensation of silicic acid butyl esters was investigated by gel permeation chromatographic (GPC) analysis. The results revealed that the condensation was greatly dependent on a degree of esterification of the esters. The ester with the lowest degree of esterification underwent condensation to form a highly polymerized ester. It was found that fibers could be drawn from the ester solution before gelation.     

Fluorescent products of the reaction of mono-substituted guanidino compounds with benzoin-dimethylformamide

The fluorescent products formed from methylguanidine or phenylguanidine and benzoin in the presence of dimethylformamide are shown to be the corresponding 2-substituted amino-4, 5-diphenylimidazoles. They fluoresce most intensely at pH 9–10 and the fluorescence is stabilized by β-mercaptoethanol.     

Efficient synthesis of optically active atropisomeric anilides through catalytic asymmetric N-arylation reaction

In the presence of (R)-DTBM-SEGPHOS-Pd(OAc)2 catalyst, N-arylation of ortho-tert-butyl-NH-anilides with 4-nitroiodobenzene proceeds with high enantioselectivity (89-95% ee) to give optically active atropisomeric anilides possessing N-C chiral axis. Furthermore, the intramolecular version of the present catalytic asymmetric N-arylation gave atropisomeric lactams with high optical purity (94-96% ee).     

Raman scattering in low wavenumber region as a new probe to structural properties of microcrystalline silicon

The structural properties of microcrystalline silicon (μc-Si) are studied by Raman scattering. It is found that the intensity of each Raman band closely correlates with the absorption coefficient in the interband region and that the Raman band at ca. 150 cm^?1 is a sensitive probe to randomness of Si-Si bonding structure in μc-Si.