Trichūr, India
Trichūr, India

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Anoop G.,Cochin University of Science and Technology | Anoop G.,Chung - Ang University | Mini Krishna K.,Cochin University of Science and Technology | Mini Krishna K.,Vimala College | Jayaraj M.K.,Cochin University of Science and Technology
Journal of the Electrochemical Society | Year: 2011

Green emitting alternating current thin film electroluminescent devices were fabricated on glass substrates in the conventional MISIM structure using ZnGa2O4:Mn as the active layer. The devices were fabricated varying the deposition time of the active/phosphor layer at two different substrate temperatures, 500 and 600°C. The active layer and top dielectric layer were deposited using rf magnetron sputtering technique. All devices gave an emission in the green region of the visible spectrum even without any post deposition annealing. The EL emission could be de-convoluted into twothree peaks attributed to the 4T1 - 6A1 transition of Mn2+ centers at various sites in the host lattice. The intensity of the 502 nm EL emission was found to increase with active layer thickness. The luminance versus voltage plots exhibit an increase in threshold voltage with increase in phosphor layer thickness. The purity of the EL emissions is gauged using CIE coordinates that are found to lie in the green region of the chromaticity diagram. © 2011 The Electrochemical Society.

Anoop G.,Cochin University of Science and Technology | Anoop G.,Chung - Ang University | Minikrishna K.,Cochin University of Science and Technology | Minikrishna K.,Vimala College | Jayaraj M.K.,Cochin University of Science and Technology
Philosophical Magazine | Year: 2012

Thin films of Eu-doped Y 2O 3 were deposited using the pulsed laser ablation technique on amorphous fused silica substrates. The effect of oxygen partial pressure (pO 2) and substrate temperature on the structural and optical characteristics of the deposited films were investigated. All the deposited films were crystalline, showing preferred orientation along the (111) plane, irrespective of oxygen partial pressure and substrate temperature. The film deposited at 0.005mbar pO 2 exhibited better crystallinity with minimum FWHM at a substrate temperature of 600°C. All the films deposited at various substrate temperatures and different partial pressure (at 600°C) exhibited a red luminescence peak at 615nm corresponding to the 5D 0 -7F 1 transition in Eu 3+. Photoluminescence excitation spectra exhibited two bands, one corresponding to band to band excitation (212nm) of the host and the other to charge transfer band excitation (245nm). A microstructure analysis revealed that surface roughness of the as-deposited films increases with increase in oxygen partial pressure. © 2012 Taylor & Francis.

Krishna K.M.,Cochin University of Science and Technology | Krishna K.M.,Vimala College | Anoop G.,Cochin University of Science and Technology | Anoop G.,Chung - Ang University | Jayaraj M.K.,Cochin University of Science and Technology
Physica Status Solidi (A) Applications and Materials Science | Year: 2012

An alternating current thin film electroluminescent (ACTFEL) device was fabricated on commercial glass substrate with dysprosium doped zinc gallate as the active layer. The phosphor layer and the top dielectric layer were deposited using rf magnetron sputtering technique. The devices fabricated with an asymmetric double insulating structure gave a white electroluminescent (EL) emission when driven by a voltage pulse frequency of 1.5kHz, even without post-deposition annealing of the active layer. Such an emission resulted from the simultaneous occurrence of multicolor transitions, characteristic of the dopant ion. The exponential dependence of luminance on applied voltage was quite evident from the luminance-voltage (L-V) curves. Devices were also fabricated with a highly crystallized interfacial layer of ZnO in between the substrate and the phosphor layer. Such devices could withstand a wider range of applied voltage, henceforth resulting in enhanced device performance. The chromatic quality of the EL emissions from both the devices were gauged using chromaticity coordinates. The CIE coordinates of fabricated ZnGa2O 4:Dy3+ ACTFEL devices (a) without and (b) with ZnO interfacial layer. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gopalan E.V.,Cochin University of Science and Technology | Malini K.A.,Vimala College | Narayanan T.N.,Cochin University of Science and Technology | Joy P.A.,CSIR - National Chemical Laboratory | And 4 more authors.
Nanoscale Research Letters | Year: 2010

Potential applications of nickel nanoparticles demand the synthesis of self-protected nickel nanoparticles by different synthesis techniques. A novel and simple technique for the synthesis of self-protected nickel nanoparticles is realized by the inter-matrix synthesis of nickel nanoparticles by cation exchange reduction in two types of resins. Two different polymer templates namely strongly acidic cation exchange resins and weakly acidic cation exchange resins provided with cation exchange sites which can anchor metal cations by the ion exchange process are used. The nickel ions which are held at the cation exchange sites by ion fixation can be subsequently reduced to metal nanoparticles by using sodium borohydride as the reducing agent. The composites are cycled repeating the loading reduction cycle involved in the synthesis procedure. X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron microscopy, Energy Dispersive Spectrum, and Inductively Coupled Plasma Analysis are effectively utilized to investigate the different structural characteristics of the nanocomposites. The hysteresis loop parameters namely saturation magnetization and coercivity are measured using Vibrating Sample Magnetometer. The thermomagnetization study is also conducted to evaluate the Curie temperature values of the composites. The effect of cycling on the structural and magnetic characteristics of the two composites are dealt in detail. A comparison between the different characteristics of the two nanocomposites is also provided. © 2010 The Author(s).

Johnson D.,Vimala College | Johnson T.,Indian Institute of Technology Madras
Materials Today: Proceedings | Year: 2015

Zinc niobates are a potential class of compositions with varied electro ceramics applications. Phase pure Zn2Nb34O87 powders were prepared by solid state ceramic route using ZnO and Nb2O5 powders in stoichiometric proportions. The structural characterization and phase purity testing is done by powder X-ray diffraction technique. The vibrational spectroscopic analysis is done by FT-IR and FT-Raman spectra. The optical properties of Zn2Nb34O87 are determined by UV-Vis spectroscopic studies. The optical band gap of the sample is determined from the tau plot of the absorbance data and K-M (Kubelka-Munk) plot of diffuse reflectance spectra. The photoluminescence emission (PL) spectra is studied. The dielectric constant and loss tangent of Zn2Nb34O87 at 1MHz is measured using a gain phase analyzer. © 2015 Elsevier Ltd. All rights reserved.

Cheruvathur M.K.,Thomas College | Jose B.,Vimala College | Thomas T.D.,Thomas College
In Vitro Cellular and Developmental Biology - Plant | Year: 2015

Rhinacanthus nasutus (L.) Kurz (family Acanthaceae) produces several important bioactive molecules. Its leaves and roots were widely used in traditional systems of medicine for the treatment of cancer and other serious diseases. In the present study, the contents of three potent natural naphthoquinone esters, rhinacanthin (RC)-C, RC-D, and RC-N, were evaluated in R. nasutus hairy root cultures. Hairy roots were induced from leaves, stems, and cotyledons following transformation with Agrobacterium rhizogenes (MTCC Strain No. 532). The highest frequency (73%) of hairy root induction was observed with cotyledons. Four media (½ Murashige and Skoog [MS], MS, Schenk and Hildebrandt medium, and Woody Plant Medium) were then compared for their effects on hairy root growth and RC production. The transgenic status of hairy roots was confirmed by PCR analysis and Southern hybridization analysis. A time course study revealed that the highest hairy root biomass (0.89 g/flask dry weight [DW]) and RC contents (RC-C, 3.8 mg/g DW; RC-D, 0.43 mg/g DW; and RC-N, 0.18 mg/g DW) were observed following culture on MS medium 6 wk after culture initiation. The root biomass (1.41 g DW/flask) and RC contents (RC-C, 4.4 mg/g DW; RC-D, 0.69 mg/g DW; and RC-N, 0.21 mg/g DW) were further increased by the use of 4% sucrose. The growth and RC production from hairy roots of R. nasutus demonstrated in the present study may offer an effective and reliable alternative for the exploitation of this medicinal plant. © 2015, The Society for In Vitro Biology.

Raphael K.R.,St. Mary's College | Madhavan M.,Vimala College
Plant Archives | Year: 2013

Phytochemicals are non-nutritive plant chemicals that have protective or disease preventing properties for the plant. The screening of phytochemical constituents in rhizome and flowers of Hedychium flavescens were performed using generally accepted laboratory technique for qualitative determinations. The phytochemical screening showed that rhizomes were rich carbohydrate, starch, sugar, protein, cardiac glycoside, phenols, saponins, alkaloids, tannin, phlobatannin and terpenoids. Carbohydrate, ketose protein, phenols, saponins and terpenoids were present in flowers.

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