Nāgercoil, India
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Bright K.C.,Malankara Catholic College | Freeda T.H.,Physics Research Center
Physica B: Condensed Matter | Year: 2010

Single crystals of l-alanine cadmium chloride (LACC), an organometallic nonlinear optical material, have been grown by the slow evaporation technique. The grown crystals were subjected to various characterization techniques, such as single crystal and powder XRD, FTIR, UVvis and TGA-DTA. The mechanical properties of the crystals show that this material belongs to the category of hard materials. Second harmonic generation was confirmed by the Kurtz and Perry powder technique. Electrical parameters, such as dielectric constant, dielectric loss, ac and dc conductivity and their corresponding activation energies have been studied. The low dielectric constant and dielectric loss suggest that this material is a good candidate for micro-electronic applications. © 2010 Elsevier B.V. All rights reserved.

Sriramachandran P.,Physics Research Center | Viswanathan B.,Sri Kaliswari College | Shanmugavel R.,Physics Research Center
Solar Physics | Year: 2013

Aluminium monoxide (AlO) is widely known for its astrophysical significance. An analysis of the prominent lines of the (2,3;3,2;3,4;4,5;4,3;5,6;6,7) bands of the B2Σ+-X2Σ+ transition with those of sunspot umbral spectral lines suggests that the AlO molecule appears to be a non-negligible component of sunspot umbrae. Results of a recent (2008) rotational analysis were used to carry out the study. The effective rotational temperature determined for the above lines in the sunspot umbral spectrum is found to be of the order of 2900 K. The radiative-transition parameters that include Franck-Condon (FC) factors, r-centroids, electronic-transition moment, Einstein coefficient, absorption-band oscillator strength, and radiative lifetime have been estimated for the experimentally known vibrational levels using the Rydberg-Klein-Rees (RKR) potential. © 2013 Springer Science+Business Media Dordrecht.

Freeda T.H.,Physics Research Center
Applied Physics A: Materials Science and Processing | Year: 2010

The single crystals of pure and Potassium doped L-alanine cadmium chloride (LACC), a metallo organic nonlinear optical material is grown by a slow evaporation technique. The grown crystals were confirmed by single crystal, powder XRD analyses and atomic absorption studies. Dielectric measurements were carried out for different frequencies at different temperatures. The dielectric constant decreases due to the introduction of large ionic radius K+ ion in the pure LACC crystal. The low dielectric constant and dielectric loss suggest that it can be used as intermetal dielectric material. © Springer-Verlag 2010.

Sakthi Sudar Saravanan R.,Physics Research Center | Pukazhselvan D.,Physics Research Center | Mahadevan C.K.,Banaras Hindu University
Philosophical Magazine | Year: 2011

Quantum dots (3-4 nm) of Zn1-xCdxS (both free of Mn2+ and with Mn2+ incorporated) were synthesized through a novel solvothermal-microwave irradiation technique. Detailed structural analysis of the Zn1-xCdxS and Zn1-xCd xS:Mn2+ (x = 0, 0.25, 0.5, 0.75 and 1) materials was carried out using powder X-ray diffraction technique. For all the compositions, the crystallite size was controlled to less than 1.5 nm. The optical energy gap for Zn1-xCdxS was found to vary from 3.878 to 2.519 eV and for Zn1-xCd1-xS:Mn2+ it varies from 3.830 to 2.442 eV when x is increased from 0 to 1. Overall, the optical energy gap could be tuned from a minimum of 2.442 eV to a maximum of 3.878 eV. DC conductivity analysis (from 40C to 150°C) and electrical energy gap analysis for all the compositions were also performed. The dc conductivity for Zn 1-xCd1-xS solid solutions varies from 0.3840 × 10-10 to 8.7782 × 10-10 mho/m at 150°C and for Zn1-xCd1-xS:Mn2+ it varies from 0.5751 × 10-10 to 9.8078 × 10-10 mho /m at 150°C (for x = 0 to x = 1). The method of synthesis and the results observed in this investigation may assist in the fabrication of optical devices when the required operational performance falls under the range observed in the study. © 2010 2011 Taylor & Francis.

Saravanan R.S.S.,Physics Research Center | Pukazhselvan D.,Banaras Hindu University | Mahadevan C.K.,Physics Research Center
Journal of Alloys and Compounds | Year: 2011

Zn(1-x)CdxS and Zn(1-x)Cd xS:Mn2+ semiconductor quantum dots (2-4 nm) have been prepared by a novel solvothermal route assisted microwave heating method. The growth parameters governing the smaller size and higher yield have been optimized. The synthesized QDs exhibit a significant blue shift as compared to their corresponding bulk counterpart in the UV-vis optical absorption spectrum. The dielectric constant value varies from 2.79 to 6.17 (at 40 °C, 1 kHz) depending upon the composition of the alloy; lower value corresponds to Zn 0.75Cd0.25S:Mn2+ and the higher value corresponds to Zn0.25Cd0.75S:Mn2+. The crystallite size to exciton bohr radius ratio being <1 indicates a strong quantum confinement effect in both CdS and ZnS QDs. The quantum confinement effect exists in the sequence of ZnS:Mn2+ < Zn (1-x)CdxS:Mn2+ (x < 0.5) < ZnS < Zn(1-x)CdxS < CdS < CdS:Mn2+. © 2011 Elsevier B.V. All rights reserved.

Gnanasambandam C.,Physics Research Center | Perumal S.,Physics Research Center
Journal of Crystal Growth | Year: 2010

A new organic nonlinear optical material l-tartaric acid-nicotinamide (LTN) has been synthesized and single crystals have been grown from its aqueous solution by slow evaporation method. The solubility of the material was measured at various temperatures in de-ionized water. Single crystal X-ray diffraction analysis reveals that the crystal belongs to monoclinic system with the space group P21. The mode of vibration of different molecular groups present in LTN was identified by FTIR spectral analysis. The UV-vis-NIR spectrum of LTN shows less optical absorption and good transmittance in the entire visible region enabling its use in optical application. Second harmonic generation (SHG) was confirmed by the Kurtz powder method. Thermo gravimetric and differential scanning calorimetric (DSC) studies were carried out to determine the thermal properties of the grown crystal. The electrical measurement was made in the frequency range 100 Hz-1 MHz and in the temperature range 313-403 K along b-direction of the grown crystal. The electrical conductivity and dielectric studies were also carried out and reported for the first time. © 2010 Elsevier B.V. All rights reserved.

Srikrishna Ramya S.I.,Physics Research Center | Mahadevan C.K.,Physics Research Center
Journal of Solid State Chemistry | Year: 2014

Pure and Mn2+ / Co2+ / Cu2+ doped (1 and 2 at.%) spherical hematite (α-Fe2O3)nanocrystals have been synthesized by a simple solvothermal method using a domestic microwave oven. XRD measurements confirm that all the seven nanocrystals prepared consist of nanocrystalline hematite phase without any other phases. The energy dispersive X-ray and Fourier transform infrared spectral analyses confirm the phase purity of the nanocrystals prepared. TEM analysis shows the average particle sizes within the range 33-51 nm. Optical absorption measurements indicate that all the three dopants enhance the optical transmittance and reflectance. A red shift is observed in the bandgap energy values estimated from optical absorption and reflectance spectra. Results of magnetic measurements made at room temperature using a vibrating sample magnetometer indicate significant changes in the magnetic properties (coercivity, retentivity and saturationmagnetization) due to doping. Results of magnetic measurements indicate significant changes in the magnetic properties. Results of AC electrical measurements made at various temperatures in the range 40-130 C and frequencies in the range 100 Hz -1 MHz indicate low dielectric constants and AC electrical conductivities and consequently show the occurrence of nanoconfined states. © 2013 Elsevier Inc.

Saravanan R.S.S.,Physics Research Center | Mahadevan C.K.,Physics Research Center
Journal of Alloys and Compounds | Year: 2012

A series of wurtzite Zn (1-x)Cd xS (x = 0, 0.25, 0.5, 0.75 and 1) nanocrystals with average crystallite size of 1.98, 1.82, 1.80, 2.04 and 2.51 nm, respectively, have been synthesized by simple solvothermal microwave heating method. The photoluminescence yield is found to be higher in the case of alloyed nanocrystals (x = 0.25, 0.5, 0.75) as compared to ZnS (x = 0) and CdS (x = 1). The optical emission is tuned from blue (440 nm) to orange (575 nm) with the increase of Cd composition in Zn (1-x)Cd xS nanocrystal. The impedance analysis for Zn (1- x)Cd xS nanocrystals has been measured as a function of frequency and temperature. The real and imaginary part of complex impedance plots exhibit semicircle behavior in the complex plane. The AC activation energies of ZnS, Zn 0.75Cd 0.25S, Zn 0.5Cd 0.5S, Zn 0.25Cd 0.75S and CdS nanocrystals were calculated from electrical conductivity analysis and are found to be 0.188, 0.378, 0.456, 0.284 and 0.255 eV, respectively. The conductivity of the alloyed nanocrystals was higher than that of ZnS and CdS. © 2012 Published by Elsevier B.V.

Saravanan R.S.S.,Physics Research Center | Pukazhselvan D.,Banaras Hindu University | Mahadevan C.K.,Physics Research Center
Journal of Alloys and Compounds | Year: 2012

This paper presents a comparative analysis of ZnS QDs synthesized by conventional and microwave heating techniques using zinc acetate and sodium sulphide reactants. The size of the quantum dots achieved by the latter technique (∼3 nm) is at least 30 times smaller than the former technique. Incorporation of excess Na 2S and microwave treatment are the important factors responsible for controlling the size of ZnS nanocrystals. Furthermore, the distribution of quantum dots is highly influenced by the addition of small amount of NaOH. The UV-vis analysis reveals that the band gap can be widened up to 3.94 eV (correspond to ∼3 nm ZnS) from 3.67 eV (correspond to bulk ZnS). Surprisingly better conductivity is observed for the widest band gap ZnS of the present study; this could be due to defects/vacancies present in the system and its influence in the band structure. The higher conductivity value is supported by the smaller activation energy value, smaller dielectric constant and higher dielectric loss, etc. The conduction is further explained by thermionic emission mechanism. © 2011 Elsevier B.V.

Ramya S.I.S.,Physics Research Center | Mahadevan C.K.,Physics Research Center
Materials Letters | Year: 2012

A simple microwave assisted solvothermal route has been developed to prepare amorphous (γ-) and crystalline (ε-, β- and α-) Fe 2O 3 nanophases. The prepared nanophases have been characterized chemically, structurally, optically and magnetically by the available methods like thermogravimetric and differential scanning calorimetric analyses, X-ray powder diffraction analysis, scanning electron microscopic and transmission electron microscopic analyses, energy dispersive X-ray spectroscopic and UV-visible spectral analyses, and vibrating sample magnetometric measurements. The average particle sizes obtained through transmission electron microscopic analysis are 19, 24, 29 and 33 nm respectively for the γ-, ε-, β- and α-Fe 2O 3 phases. Results obtained in the present study indicate that the method adopted is an effective one for preparing the γ-, ε-, β- and α-Fe 2O 3 nanophases with good purity, stoichiometry, homogeneity, and optical and magnetic properties. © 2012 Elsevier B.V.

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