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Pathanāmthitta, India

Varughese G.,Catholicate College
Materials Today: Proceedings | Year: 2016

Zinc Sulphide doped with Gadolinium (ZnS: Gd) quantum dots have various scientific and engineering applications in electronics, nonlinear optical devices for communication, and optical computers. The material is an excellent light transmission material with high refractive index 2.27, makes useful in photonic crystal devices that operate in the region from visible to near infrared. ZnS:Gd nano materials with an average particle size of 18-23 nm are synthesized by the reaction of Zinc acetate, Hydrogen Sulphide and Gadolinium oxide by chemical route technique. XRD, SEM, EDAX and FTIR characterize the samples. The average crystal size of the prepared ZnS: Gd nanopowder is determined by XRD. Band gap values Gd3+ doped ZnS were determined to 4.11 eV from the optical absorption studies of the as-prepared samples and exhibited a redshift towards 301 nm in comparison with undoped ZnS nanoparticles and a blue shift was observed relative to bulk ZnS. © 2016 Elsevier Ltd.

Joseph S.A.,Cochin University of Science and Technology | Mathew S.,Cochin University of Science and Technology | Sharma G.,Cochin University of Science and Technology | Hari M.,Cochin University of Science and Technology | And 3 more authors.
Plasmonics | Year: 2010

We have performed thermal diffusion measurements of nanofluid containing gold and rhodamine 6G dye in various ratios. At certain concentrations, gold is nearly four times more efficient than water in dissipating small temperature fluctuations in a medium, and therefore it will find applications as heat transfer fluids. We have employed dual-beam mode-matched thermal lens technique for the present investigation. It is a sensitive technique in measuring photothermal parameters because of the use of a low-power, stabilized laser source as the probe. We also present the results of fluorescence measurements of the dye in the nanogold environment. © Springer Science+Business Media, LLC 2010.

John J.,Catholicate College | Thomas L.,Catholicate College | George N.A.,Baselius College | Kurian A.,Catholicate College | George S.D.,Manipal University India
Physical Chemistry Chemical Physics | Year: 2015

Dye-nanoparticle mixtures hold great promise in biological as well as photonics applications due to their capability to tailor the emission behavior of dye by tuning the nanoparticles parameters. However, as compared to the well-defined dye-nanoparticle distance, studies lack the understanding of homogenous mixtures of dye and nanoparticles. In this work, we investigate the influence of shape and concentration of gold nanoparticles prepared via green synthesis on the optical properties of fluorescein dye in a dye-nanoparticle mixture. We have investigated the radiative path of deexcitation using steady state fluorescence and the non-radiative path is probed using a laser based dual-beam thermal lens technique. The energy transfer efficiency as well as dye-nanoparticle distance is studied using both techniques. Furthermore, we have explored the influence of nanoparticles parameters on the fluorescence quantum yield of fluorescein using the thermal lens technique. The studies indicate that spherical nanoparticles are efficient quenchers while star shaped nanoparticles can probe larger dye-NP distances. The tailoring of dye properties by tuning nanoparticle parameters can be utilized in diverse areas including bioimaging, solar cells, and sensors. © the Owner Societies 2015.

Kumar B.R.,Catholicate College | Basheer N.S.,Catholicate College | Kurian A.,Catholicate College | George S.D.,Manipal University India
International Journal of Thermophysics | Year: 2013

A study on energy transfer from the Rhodamine 6G (donor) to gold nanopar-ticles (acceptor) is investigated using a laser-based dual-beam thermal-lens technique. The nanoparticles are observed to quench the intrinsic fluorescence of the dye molecule via a nonradiative energy transfer mechanism. The influence of nanoparticle concentration (0.09 nM to 0.24 nM) on the energy transfer mechanism with Rhodamine 6G (1 μM) is investigated. Analysis of the results indicates that the energy transfer efficiency is high (more than 50 %) in the presence of nanoparticles and the efficiency is enhanced with an increase in the nanoparticle concentration. The distance between the nanoparticle and dye molecule is evaluated on the basis of the nanomaterial surface energy transfer model. The thermal-lens studies probe the nonradiative path of de-excitation of the excited molecule, and the comparison between this technique and the conventional fluorescence method in measuring the distance as well as the energy-transfer efficiency clearly indicates that the thermal-lens technique is a complementary approach to study the energy-transfer mechanism between a donor and an acceptor. © Springer Science+Business Media New York 2013.

Kumar B.R.,Catholicate College | Basheer N.S.,Catholicate College | Kurian A.,Catholicate College | George S.D.,Manipal University India
Applied Physics B: Lasers and Optics | Year: 2014

Tailoring optical properties of the dye molecules using metal nanoparticles is a burgeoning area of research. In this work, we report our results on the studies of how the absorption and emission behavior of Rhodamine 6G dye is tailored using gold nanoparticles. Furthermore, the influence of dye concentration on these properties for a given concentration of nanoparticles in the dye-nanoparticle mixture is investigated. In addition, the difference between the concentration-dependent fluorescence quantum yield of the dye molecules is measured in the absence and presence of nanoparticles using the dual-beam thermal-lens technique. Our absorption spectral studies show additional spectral features due to nanoparticle aggregation on interaction with cationic Rhodamine 6G dye. Dye concentration-dependent steady-state fluorescence studies in the presence of nanoparticles indicate a blue shift in peak fluorescence emission wavelength. The quantum yield value measured using thermal-lens technique exhibit a non-monotonic behavior with dye concentration with substantial quenching for lower dye concentrations. The results are interpreted in terms of dye-nanoparticle interaction and the formation of dye shell around the nanoparticle. © 2013 Springer-Verlag Berlin Heidelberg.

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