NOPR Community:

Spectroscopic studies of molluscan shells

Mon, 01 Nov 2004 00:00:00 GMT

Title: Spectroscopic studies of molluscan shells Authors: Konwar, R; Changmai, R; Baruah, G D Abstract: The spectral characteristics of few naturally occurring molluscan shells have been investigated with the help of laser induced fluorescence, X-Rays, absorption and FTIR spectroscopic techniques. The laser induced fluorescence (LIF) or the stimulated laser induced fluorescence from molluscan shells exhibits diffuse bands in the region 5860-6350 Ǻ and some discrete bands in the region 5000-5400Ǻ. The fluorescence spectra of different shells are found to be different. The FTlR spectra show predominantly the vibrational bands of CaCO₃. But there are additional bands, which are not characteristic of CaCO₃. The X-ray photograph and iridescence pattern of few shells are presented. Page(s): 812-815

Blue electroluminescence in organic semiconductors

Mon, 01 Nov 2004 00:00:00 GMT

Title: Blue electroluminescence in organic semiconductors Authors: Misra, Aparna; Kumar, Lokendra; Kumar, Pankaj; Dhawan, S K; Kamalasanan, M N; Chandra, Subhas Abstract: Light emitting diodes based on organic materials are of considerable interest owing to their attractive characteristics and potential applications in flat panel displays. This paper focuses on some important blue light emitting organic materials. Particularly the attention has been paid to the absorption, photoluminescence (PL), electroluminescence (EL) spectra, current-voltage (1-V) and luminescence-voltage (L- V) characteristics of blue light emitting organic semiconductors, as well as those of the para-hexaphenyl (PHP). Syntheses of some important blue light emitting materials have also been discussed. Para hexaphenyl (PHP), which was synthesized by the conventional Kovacic method, is one of the important blue light emitting π-conjugated oligomers. OLEDs fabricated, using PHP as an emitter, TPD and PBD as the hole transport layer and electron transport layer respectively, gave efficient blue electroluminescence. The photoluminescence (PL) and electrolurninescence (EL) of PHP occur at 423 nm, indicating PHP as an excellent blue emitter. This oligomer showed strong absorption peaks at 297 and 318 nm. The devices showed non-linear electrical properties and bright electroluminescence with low turn on voltages (9V). Some of our most recent work in the development of a variety of blue light emitting devices has been included and discussed in detail. Page(s): 793-805

Analysis of coupling characteristics of rectangular core optical waveguide coupler

Wed, 01 Sep 2004 00:00:00 GMT

Title: Analysis of coupling characteristics of rectangular core optical waveguide coupler Authors: Engles, D; Malik, S S Abstract: A theoretical formulism based on the boundary matching technique has been proposed to study the systematic of an asymmetric waveguide coupler. Same formulism is applicable to a symmetric coupler. The equivalent parallel coupling length to account for the coupling in the two S-shaped regions in the input and the output of the coupler is obtained from the coupler geometry and is dealt with more accurately and sensitively in our calculations. No fitting parameter is required for our calculation. The calculated characteristics of the asymmetric coupler are very close to those of experimental ones. Our model can aid in the design of diffused channel single mode rectangular core optical waveguide couplers. Page(s): 674-683

Crystal and molecular structure of antimony thiourea bromide

Sun, 01 Aug 2004 00:00:00 GMT

Title: Crystal and molecular structure of antimony thiourea bromide Authors: Shettigar, V; Bhat, S G; Dharmaprakash, S M Abstract: The structure of antimony thiourea bromide hydrate (ATB) with molecular formula Sb[SC(NH₂)₂]Br₃.H₂O has been determined by X-ray single crystal diffraction. ATB crystallizes in the orthorhombic system with the lattice parameters a = 12.272(3)Ǻ; b =11.675(4)Ǻ; c =18.617(5)Ǻ; the space group is Cmc2₁, Z = 8, and D_c = 2.648Mg/m³. The final R = 0.0366 (wR = 0.0914) for 1273 reflections. The asymmetric unit consists of two symmetrically independent halves of a complex Sb[SC(NH₂)₂]Br₃] and one crystal water molecule, which are completed to a complex dimer by the mirror plane of the space group. The whole crystal is found packed in mm2 point group, which is non-centrosymmetric arrangement of atoms. Page(s): 581-584