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Virudhunagar, India

Das D.,Cotton College | Konwar R.,Cotton College | Kalita P.K.,Nano Science Research Laboratory
Indian Journal of Physics | Year: 2015

Starch capped PbS, CdS and PbS–CdS nanocomposites are conjugated with Calf–Thymus DNA. All the materials are characterized by X-ray diffraction, high-resolution transmission electron microscopy, UV–Vis spectroscopy and photoluminescence spectroscopy. The x-ray diffraction patterns of PbS and CdS show that the materials possess polycrystalline having both cubic and hexagonal phases. High resolution transmission electron microscopic results (HRTEM) shows PbS nanoparticles of size 3 nm and that of CdS nanoparticles having average size 4 nm which exhibit tendency of agglomeration. In case of PbS/CdS, it exhibits different types of nanosheets. The UV absorption spectra of all the samples exhibit clear blue-shift with the respective bulk absorption edges. This is attributed to the strong quantum confinement in the materials. The absorption spectra also exhibit increase of the band gaps from 2.25 to 4.35 eV for PbS; 2.25–4.2 eV for CdS with decrease of molarities from 0.1 to 0.001 M as well as conjugated with DNA. The photoluminescence spectra of all PbS, CdS and PbS/CdS composites synthesized at 0.1 M molar concentration show a further blue shift and an enhancement of intensity after conjugation with DNA, but the effect is reversed i.e. occurrence of red shift and reduction of intensity for those having 0.01 M. This is due to the two competing processes of surface passivation as well as stabilization of nanocomposites governed by bio-molecules and that of Dexter energy transfer with the effective charge separation. The result shows the applicability of the materials in development of biological labels and biosensors. © 2015 IACS. Source

Saranya A.,Nano Science Research Laboratory | Pandiarajan J.,Nano Science Research Laboratory | Jeyakumaran N.,Nano Science Research Laboratory | Prithivikumaran N.,Nano Science Research Laboratory
International Journal of ChemTech Research | Year: 2014

Fabrication of TiO2 thin films was carried on microscopic glass substrates by sol-gel spin coating method using Titanium tetra isopropoxide (TTIP) as an initiating inorganic precursor. Films with different post annealing temperatures and varying number of layers were coated. It has been observed from XRD study that the size of crystallites of TiO2 film was found to increase with increase in both annealing temperature and number of coatings. UV-Visible spectrometric measurements revealed that the transmittance of the film and the band gap values, calculated from Tauc's relation, were found to decrease with increase in both film thickness and annealing temperatures. Two emission peaks at 485 nm & 502 nm were observed in Photoluminescence spectrum of all the films. Changes in the surface morphology of the films were investigated using FESEM studies. The resistivity decreases with increase in number of coatings. The obtained results show that the post annealing temperature and the number of coatings have influence over the physical properties of TiO2 thin films. Source

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