Faculty Publications

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Author: search.filters.author.Mahendra, K.Subject: search.filters.subject.Photoluminescence

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    Synthesis and Optical Characterization of Amaranth Dye Doped Thiourea Barium Chloride (TBC) Single Crystals
    (Elsevier Ltd, 2018) Mahendra, K.; D'Souza, A.; Ifthekarahmed; Udayashankar, N.K.
    Thiourea barium chloride (TBC), Amaranth doped (0.05, 0.1 mM) TBC(ADTBC) crystals were synthesized at room temperature by solvent evaporation process. Structural analysis of TBC and ADTBC were studied using powder XRD, results confirmed that dye got incorporated into the host lattice. Optical analysis of the TBC and ADTBC crystals were carried using UV-Visible and photoluminescence spectrophotometer. Results showed that both pure and dye doped crystals had an absorption peak at around 264 nm. Optical bandgap of the crystal was found to be decreasing as the doping percentage of the crystal increased. Pure and doped crystals exhibit a strong emission peak in the blue region. © 2017 Elsevier Ltd.
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    Synthesis, structural, optical and electrical (DC) properties of a semiorganic Thiourea Barium Chloride (TBC) single crystal
    (Elsevier GmbH journals@elsevier.com, 2017) Mahendra, K.; D'Souza, A.; Udayashankar, N.K.
    In the present study, TBC single crystals were synthesized using solution evaporation method. The structural analysis of TBC crystal was studied using Powder X-ray diffraction. Optical properties of TBC crystals were carried out using UV–vis, FTIR, Raman and photoluminescence (PL) spectra. The crystal shows absorbance maxima at 209 nm and transparent in the visible region 300–900 nm. The various optical constants such as refractive index, reflectance, speed of light, extinction coefficient, electrical susceptibility, dielectric constant, optical and electrical conductivity were evaluated. Thus results revealed that all these optical constants shows a strong dependence on optical absorption coefficient. Using single oscillator model (Wemple ?Didomenico), lattice dielectric constant and the ratio of free charge carrier to their effective mass were evaluated. The PL study of TBC crystals shows two emission peaks (419 nm ?S, 441 nm- Ba) in blue region. The DC resistivity and conductivity of the crystal was investigated in the temperature range 26 °C–115 °C. © 2017 Elsevier GmbH
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    Effect of Zn doping on the structural, optical, photoluminescence and mechanical properties of thiourea barium chloride (TBC) crystal
    (Elsevier Ltd, 2017) Mahendra, K.; D'Souza, A.; Udayashankar, N.K.
    In the present work, a synthesis and comparative study on the effect of Zinc (Zn) on thiourea barium chloride (TBC) single crystals has been reported. Crystals of thiourea barium chloride and Zn-doped thiourea barium chloride crystals are prepared using slow evaporation from the saturated solution. The samples were subjected to single crystal and powder X-ray diffraction to study the unitcell parameters and structural variations. The functional groups present in the crystals are derived using FTIR and Raman analysis. The enhancement of transmittance with the addition of Zn and the variations in the parameters such as bandgap, extinction coefficient, reflectance, refractive index, optical and electrical conductivity, real and imaginary part of dielectric constant are studied from UV–vis spectrum analysis. Vickers hardness measurements are conducted for pure and Zinc-doped TBC single crystals. The emission spectrum of pure and Zn doped single crystals are studied using photoluminescence analysis. © 2017 Elsevier Ltd
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    Effect of Erioglaucine dye dopant on the structural, optical, mechanical, electrical and nonlinear properties of ammonium dihydrogen phosphate single crystal
    (Elsevier B.V., 2020) Fernandes, J.M.; Mahendra, K.; Udayashankar, N.K.
    The structural, optical, mechanical, electrical and nonlinear properties of standard Ammonium Dihydrogen Phosphate (NH4H2PO4, ADP) single crystals incorporating organic Erioglaucine dye dopant are presented. The effect of Erioglaucine dye dopant at varied concentration on these properties has been investigated through measurement of powder X-Ray Diffraction (XRD), UV–Vis and photoluminescence spectroscopy, Vickers microhardness, light dependent I–V measurements and Second Harmonic Generation studies. These measurements reveal that doping with increasing dye concentration of Erioglaucine leads to change in properties of the ADP single crystals, making them suitable for optoelectronic applications. The Erioglaucine doped ADP single crystals were grown using solvent evaporation technique at room temperature. Optical properties like absorbance and emission of these crystals are determined using UV–vis and photoluminescence spectroscopy, respectively. Optical bandgap and photoluminescence of the crystals are found to increase with dye doping, indicating their suitability in photonic applications. The mechanical properties of the crystals are determined using Vickers microhardness measurement technique. Light dependent I–V measurements exhibit negative photoconductivity behavior of the ADP crystals. However, the current through the crystals is observed to increase with increase in doping concentration of the Erioglaucine dye. Second Harmonic Generation studies show enhancement in nonlinearity for doped crystals. Our experiments indicate gradual variance in the crystallinity, emission, hardness, conductivity and nonlinearity of the sample with change in dye concentration. © 2020 Elsevier B.V.
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    A novel approach to the synthesis of semiorganic ammonium hydrogen oxalate oxalic acid dihydrate single crystal and its characterization
    (Springer Science and Business Media B.V., 2021) Mahendra, K.; Fernandes, J.M.; Udayashankar, N.K.
    A different approach used in the synthesis of ammonium hydrogen oxalate oxalic acid dihydrate (NH4H3(C4O8)·2H2O) single crystals is presented. The crystals are synthesized using solvent evaporation technique. The analysis of the synthesized NH4H3(C4O8)·2H2O single crystals has been carried out through measurements such as single-crystal X-ray diffraction (SCXRD), powder XRD, UV–Vis and photoluminescence spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analysis (TG–DTA), Vickers microhardness measurements and current versus voltage (I–V) characteristics. The evaluation of the molecular structure of the crystals using SCXRD shows that they belong to the triclinic crystal system with space group P-1. The structural properties of the crystals are also evaluated using powder XRD measurements on their finely crushed powder. These measurements corroborate the results of SCXRD and confirm the triclinic system of the crystals. The optical properties like absorbance and emission of these crystals are determined using UV–Vis and photoluminescence spectroscopy, respectively. These measurements show that the crystals exhibit substantial emission in the blue region. The thermal stability and the decomposition mechanism of the crystals is studied using TG–DTA analysis. The mechanical strength of the crystals is determined using Vickers microhardness technique. The photoresponse of the NH4H3(C4O8)·2H2O crystals is analyzed from light-dependent I–V characteristics, and it is observed that the crystals exhibit photoresistive behavior. © 2020, Akadémiai Kiadó, Budapest, Hungary.
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    Insight into the Structural and Physical Properties of Semiorganic KHOOD Single Crystal
    (Springer Science and Business Media Deutschland GmbH, 2022) Mahendra, K.; Fernandes, J.M.; Udayashankar, N.K.
    A metal–organic hybrid compound named potassium hydrogen oxalate oxalic acid dihydrate (KH3(C4O8)·2H2O) single crystal (KHOOD) is synthesized using a facile and different approach. The obtained crystals are thoroughly investigated using single crystal XRD (SCXRD), powder XRD (PXRD), UV–Vis absorption, photoluminescence, TGA-DTA and dielectric measurements. The crystal system is confirmed and the structure of the crystal is solved using single crystal X-ray diffraction (SCXRD) analysis to the R value of 0.024. The PXRD measurements are employed to evaluate the structural properties of the crystal. Absorption measurements are carried out in the UV–visible region, and photoluminescence measurements show strong blue emission at 427 nm. Thermal stability and degradation in the crystal is explored using TGA-DTA analysis. Frequency dependent electrical response of the crystal is investigated and parameters such as frequency dependent complex dielectric constant, complex impedance, loss factor, ac conductivity and Cole–Cole plots are determined. These results demonstrate the feasibility of facile synthesis of KH3(C4O8)·2H2O single crystal used in modern optoelectronic applications. © 2022, The Tunisian Chemical Society and Springer Nature Switzerland AG.