Pathanāmthitta, India
Pathanāmthitta, India

Time filter

Source Type

John J.,Catholicate College | Thomas L.,Catholicate College | Kurian A.,Catholicate College | George S.D.,Manipal University India
Microporous and Mesoporous Materials | Year: 2017

Nanotechnology offers the potential for creating new optical imaging agents with novel properties which has been used in molecular imaging and photothermal therapy. Mesoporous silica materials have attained great attention in industry due to its high thermal and chemical stability and non toxic behavior. The performance of mesoporous silica materials depends on composition, morphology and structure of made-up materials. The synthesis of mesoporous silica nanoparticles is highly sensitive because the size, morphology and pore structure changes with small change in procedure. Surface modification of mesoporous enables to incorporate metal nanoparticles in to its pores by co-condensation and post-synthesis method and hence an enhancement in optical and thermal properties of mesoporous silica nanoparticles. In the present work, we have synthesized gold nanoparticles incorporated mesoporous silica by three methods such as non functionalized, co-condensation and post-synthesis modification which is denoted as sample I, sample II and sample III. Thermal parameters such as thermal diffusivity and effusivity of the synthesized samples are measured by thermal lens and photoacoustic techniques respectively. From the values of thermal diffusivity and effusivity, thermal conductivity is estimated and a high value of thermal conductivity is obtained for sample II because of the proper encapsulation of gold nanoparticles in mesoporous silica. The influence of Rhodamine 6G concentrations on the thermal parameters of mesoporous silica is also studied which shows that thermal conductivity decreases with the addition of higher concentration of Rhodamine 6G due to the interface thermal resistance effects. In addition, we have investigated the influence of gold nanoparticle incorporated mesoporous silica on the emission properties of Rhodamine 6G and fluorescein dyes. Irrespective of dye concentration, due to plasmonic field effect and non aggregation of dye molecules, the fluorescence signal is enhanced for both dyes with the addition of gold incorporated mesoporous silica. © 2017 Elsevier Inc.

Varughese G.,Catholicate College | Santhosh Kumar A.,Mahatma Gandhi University | Louis G.,Cochin University of Science and Technology
Physica B: Condensed Matter | Year: 2010

Elastic anomalies in Potassium Sulphamate, (KNH2SO3), above room temperature were detected from temperature variation of elastic constants measured by ultrasonic Pulse Echo Overlap technique. Potassium Sulphamate has been reported to be a ferroelectric and piezo electric material. The elastic constants C11, C44, C55 and C66 have exhibited weak anomalies around 350 K. The DC conductivity measurement along a, b, and c axes also supports this conclusion. © 2010 Elsevier B.V. All rights reserved.

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.

Thomas L.,Catholicate College | John J.,Catholicate College | Kumar B.R.,Catholicate College | George N.A.,Baselius College | Kurian A.,Catholicate College
Materials Today: Proceedings | Year: 2015

Dual beam Thermal lens technique is employed the thermal diffusivity of gold nanoparticle is synthesized using polyvinyl alcohol as reducing agent. The photoluminescence spectra of all the samples are carried out. The weight ratio of gold chloride increases the fluorescence peak shift towards lower wavelength and its fluorescence intensity decreases. Also the thermal diffusivity of gold nanofluid increases as the weight ratio of gold chloride increases. © 2015 Elsevier Ltd.

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.

Anitha,Stcyrils College Adoor | Usha,Stcyrils College Adoor | Jithin,Catholicate College | Christy,Catholicate College | Varughese,Catholicate College
Materials Today: Proceedings | Year: 2016

Zinc Oxide is an extensively studied group II-VI Semiconductor with optical properties that permits stable emission at room temperature, having immense applications in sensors, field emission and photonic devices. It exhibits a wide variety of morphologies in the nano regime. XRD, FTIR, EDAX and TEM spectra have been used for characterizing the material. The percentage of doping material is confirmed from the EDAX spectrum. The XRD results indicated that the particle size of nano ZnO: Er is much small as compared to that of pure ZnO and decreases with the Erbium loading. XRD has shown that as temperature increases, particle size also increases. The UV Absorption spectra showed blue shift towards 208 nm due to doping with Er. From the position of the absorption spectra is shifted towards the lower wavelength side or known as blue-shifted relative to undoped ZnO. The band gap energy of Er-doped ZnO nanoparticles at 120 and 200oC are determined using Tauc plot and found to be in the range 3.321 eV. It was found that energy band gap Eg increases with doping of Er. As temperature increases the band gap energy decreases. The Photo-Luminescence study was carried out on this material and observed longer wavelength shift for emission peaks on calcination. The analysis of optical properties shows that ZnO: Er is a promising material and has potential application in optoelectronic devices. Doping of Er changed the free carrier concentration in the ZnO nanoparticles. © 2015 Elsevier Ltd.

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.

Varughese G.,Catholicate College
Bulletin of Materials Science | Year: 2016

The ultrasonic pulse echo overlap technique (PEO) has been used to measure the velocities of 10 MHz acoustic waves in sulphamic acid single crystals in the range of 300-400 K. This study evaluated all the elastic stiffness constants, compliance constants and Poisson's ratios of the crystal. The temperature variations of the elastic constants have been determined. The phase transition studies above room temperature were investigated using ultrasonic PEO technique. This study has suggested new weak elastic anomalies for the crystal around 330 K. The transverse elastic constants C44 and C66 have shown clear thermal hysteresis of 2 K. The present differential scanning calorimetric (DSC) studies carried out at a slow heating rate have also suggested weak phase transition around 331 K. The present elastic and thermal studies have been substantiated by already reported DC electrical conductivity studies around 330 K. © Indian Academy of Sciences.

Shemeena Basheer N.,Catholicate College | Rajesh Kumar B.,Catholicate College | Kurian A.,Catholicate College | George S.D.,Manipal University India
Journal of Luminescence | Year: 2013

Manipulation of the characteristics of laser dyes using metal nanoparticles is one of the rapidly growing areas in nanotechnology due to their promising applications in diverse fields, ranging from biomedical imaging to green energy. The energy transfer behavior of a silver nanoparticle (Ag NP) with a dye molecule, Rhodamine 6G (Rh 6G), is interrogated using static photoluminescence as well as a laser based dual beam thermal lens technique. Spherical Ag NPs of various concentrations are prepared using chemical reduction method and is mixed with a fixed concentration of Rh 6G. It is observed that the intrinsic fluorescence of Rh 6G (1×10-6 M) is quenched in proximity of the Ag NPs and the quenching efficiency increases with an increase in Ag NP concentration (2.5×10-4-10×10-4 M). The dye-NP distance is evaluated by varying the concentrations of Ag NPs and it is found to decrease with an increase in the NP concentration in the mixture from 92 to 69 Å (1 Å=10-10 m). The distance dependent energy transfer efficiency showed that dye-NP mixture follows R-4 dependence, where R is the dye-NP distance. © 2013 Elsevier B.V.

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.

Loading Catholicate College collaborators
Loading Catholicate College collaborators