Faculty Publications
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Item Optoelectronic properties of novel alkyl-substituted Triphenylamine derivatives(Elsevier B.V., 2017) Fernandes, J.M.; Swetha, C.; Appalnaidu, E.; Navamani, K.; Rao, V.J.; Satyanarayan, M.N.; Umesh, G.Hole transport characteristics in three new organic compounds based on triphenylamine (TPA) moiety are presented. The effect on electrical and optical properties of TPA, attached with methyl or tert-butyl side groups, has been investigated through measurement of current density versus voltage (J-V), capacitance versus voltage (C-V), frequency dependent capacitance, ac conductivity, Impedance spectroscopy, UV-Vis spectroscopy, Photoluminescence (PL) spectroscopy and X-Ray Diffraction (XRD) studies. These measurements reveal that, the attachment of methyl or tert-butyl group in the para-position of the TPA moiety leads to improved optoelectronic properties and greater molecular stability. XRD analysis of the samples indicates that the inter-molecular distance is the lowest for TPA with tert-butyl side group (3.43 Å) as compared to pure TPA (3.57 Å). This leads to stronger inter-molecular interaction as evidenced by the UV-Vis spectra. PL studies indicate significant Quantum Efficiency (?30%) for alkyl attached TPA. In order to get a better understanding of the charge transport phenomena, the effect of molecular structure dynamics on charge transfer kinetics is analyzed by evaluating the charge carrier hopping rate coefficient and dynamic state factor. The dynamic state factor b has higher value for lower bias voltage, corresponding to dc conductivity, whereas, at higher bias, the value of b is smaller, indicating the dominance of ac conductivity. Hopping conductivity is seen to be highest for the device with tert-butyl substitution in TPA moiety. Our experiments indicate an order of magnitude enhancement in charge carrier mobility for alkyl-substituted TPA. © 2017 Elsevier B.V.Item 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.Item 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.