Rhodamine-19 (Rh-19) incorporated three types of sol–gel samples (mentioned as dope route-I, dope route-II and dip method) were prepared by using two different methods of dye impregnation. The photophysical properties of all the three types of Rh-19 incorporated sol–gel solids were studied by using the UV–Visible absorption and the fluorescence spectroscopy. A single photon counting technique was used to estimate the lifetime of fluorescent species. From the study of fluorescence spectra, the coexistence of dimers (fluorescent and non-fluorescent both) and monomer of Rh-19 was observed. The photophysical properties of Rh-19 were found to be the best in dip sample, medium in dope route-II sample and low in dope route-I sample. After studying photophysical properties, the samples were subjected to laser study under nitrogen laser pumping at 337.1 nm at the rate of 1.5 Hz in transverse dye laser cavity. The highest laser efficiency and photostability of the dye were observed in dip sample, medium in dope route-II sample and small in dope route-I sample. A comparison between photophysical properties and laser performance of these materials showed a very good correlation. 相似文献
This review article attempts to present a comprehensive picture of the progress in selective epitaxial growth (SEG) of cubic silicon carbide (3C-SiC) to make it a cheap and practical material for high temperature and high power, high frequency and MEMS (Micro Electromechanical Systems) applications. Selective epitaxial growth followed by epitaxial lateral overgrowth (ELO) is a suitable approach to minimize the interfacial defects and other planar defects in case of thin film growth. Different techniques of SEG and its application to Si, GaAs and III–V nitrides are reviewed briefly in the first section of this article. Various SEG techniques like epitaxial lateral overgrowth, pyramidal growth and pendeo epitaxial growth, etc. have been discussed extensively for growing 3C-SiC on Si, together with the characterization of the grown films. The influence of various experimental parameters such as temperature of growth, choice of mask material, influence of an etchant, pattern shape and size, etc. is also discussed. On the basis of these data, it is believed that SEG and related techniques are a promising approach for heteroepitaxial growth of 3C-SiC films useful for devices and MEMS applications. 相似文献
We have studied the properties of various isomers of potassium clusters containing even number of atoms ranging from 2 to 20 at the ab initio level. The geometry optimization calculations of the isomers of each cluster are performed by using all-electron density functional theory with gradient corrected exchange-correlation functional. Using the optimized geometries of different isomers we investigate the evolution of binding energy, ionization potential, and static polarizability with the increasing size of the clusters. The polarizabilities are calculated by employing M?ller-Plesset perturbation theory and time-dependent density functional theory. The polarizabilities of dimer and tetramer are also calculated by employing large basis set coupled cluster theory with single and double excitations and perturbative triple excitations. The time-dependent density functional theory calculations of polarizabilities are carried out with two different exchange-correlation potentials: (i) an asymptotically correct model potential and (ii) within the local density approximation. A systematic comparison with the other available theoretical and experimental data for various properties of small potassium clusters mentioned above has been performed. These comparisons reveal that both the binding energy and the ionization potential obtained with gradient-corrected potential match quite well with the already published data. Similarly, the polarizabilities obtained with M?ller-Plesset perturbation theory and with model potential are quite close to each other and also close to experimental data. 相似文献
The preparation and characterization of porous scaffolds from chitosan-PCL blends by freeze extraction, freeze gelation and freeze drying is reported. Using freeze extraction, stable structures were obtained only from PCL, but these were not porous. No stable scaffolds were obtained using the freeze gelation process. Stable scaffolds of chitosan/PCL mixtures could not be obtained using 77% acetic acid by any of these techniques. With 25% aqueous acetic acid, stable scaffolds of chitosan/PCL mixtures were obtained by the freeze drying technique. The stability and pore morphology of freeze dried scaffolds were dependent on the relative mass ratio of chitosan and PCL. A chorioallantoic membrane assay showed that formed 3D chitosan/PCL mixtures were not toxic to vasculature. 相似文献
A synthetic route to bis-indolyldihydroxybenzoquinones was adapted for parallel organic synthesis. The route involves selective conjugate addition of an indole to dichlorobenzoquinone promoted by Br?nsted acid, followed by a Lewis acid-promoted conjugate addition of a second indole and a final hydrolysis. Methods for high-throughput purification of the products of this synthesis were also developed. Using these methods, we prepared a library whose structures are based on asterriquinone natural products, which have a wide range of biological activities. In this report, the activities of the library members in activation of the insulin receptor on mammalian cells were examined. Novel compounds were discovered that fall outside earlier developed structure-activity relationships for insulin mimics, supporting the value of systematic investigation (inspired by Nature) for the discovery of novel biologically active molecules. 相似文献
An unusual and unexpected synthesis of 3-(2-(arylamino)thiazol-4-yl)-2H-chromen-2-ones has been observed by the reaction of ethyl 2-(chloromethyl)-2-hydroxy-2H-chromene-3-carboxylate with various arylthioureas in ethanol under mild reaction conditions with excellent yields. The ambiguity in the structure of the obtained products has been solved by recording its single-crystal X-ray analysis. This protocol has been found to be a novel approach for the preparation of title compounds via benzopyran ring opening. A systematic plausible mechanism has been proposed for the formation of the product. Also, an efficient one-pot three-component method has been demonstrated for the formation of title compounds starting from salicylaldehyde.
The average and local thermal conductivity measurements of water-based Ag-nanofluid held in polypropylene and metallic containers using transient hot-wire method revealed a new phenomenon. The local thermal conductivity of water-based Ag nanofluid measured at different locations of containers was found to depend strongly upon the metallic container, but not on the polypropylene container. Similar observations have been found in water-based NiAl nanofluid, but not in water-based Al2O3 nanofluid. In contrast, this phenomenon was not observed for ethylene glycol-based Ag nanofluid, possibly due to the insignificant charge on the container wall, which partly explains the diversity in thermal conductivity by different researchers. 相似文献
Rhodamine-6G (Rh-6G) is embedded in sol-gel glass samples which have been prepared by three different methods namely: 1) using
HCl as catalyst and glycerol as Drying Control Chemical Additive (DCCA), 2) using HCl as catalyst at 60 °C and drying at room
temperature and 3) using HCl as catalyst at 60 °C and heated at 600 °C for 3 h. Comparative studies of spectroscopic and lasing
properties of the three types of Rh-6G containing samples were carried out with the lapse of time upto 8 months. Photostability
of Rh-6G containing sol-gel samples is measured in terms of half life under Nitrogen laser pumping as number of pulses of
N2 laser necessary to reduce the dye laser intensity to 50% of the original value and value is 7500 pulses at 1.67 Hz rate.
The best performance of Rh-6G, as far as its spectroscopic and lasing properties are concerned was found in third type of
host matrices using HCl as catalyst at 60 °C and heated at 600 °C for 3 h. 相似文献