Faculty Publications
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Item Studies on third-order nonlinear optical properties and reverse saturable absorption in polythiophene/poly (methylmethacrylate) composites(Springer Verlag, 2009) Poornesh, P.; Umesh, G.; Hegde, P.K.; Manjunatha, M.G.; Manjunatha, K.B.; Vasudeva Adhikari, A.V.We report here the studies on third-order nonlinear optical properties of two novel polythiophene composite films investigated using the Z-scan technique. The measurements were carried out using a Q-switched, frequency doubled Nd:YAG laser producing 7 nanosecond laser pulses at 532 nm. Z-scan results reveal that the composite films exhibit self-defocusing nonlinearity. The real and imaginary parts of the third-order nonlinear optical susceptibility were of the order 10-12 esu. The effective excited-state absorption cross section was found to be larger than the ground state absorption cross section, indicating that the operating nonlinear mechanism is reverse saturable absorption (RSA). The polythiophene composite films also exhibit good optical power limiting of the nanosecond laser pulses. The nonlinear optical parameters are found to increase on increasing the strength of the electron-donor group, indicating the dependence of ? (3) on the electron-donor/acceptor units of polythiophenes. © 2009 Springer-Verlag.Item Evolutionary algorithm based structure search and first-principles study of B12C3polytypes(Elsevier Ltd, 2017) Harikrishnan, H.; Ajith, K.M.; Chandra, S.; Mundachali Cheruvalath, V.The structure search based on evolutionary algorithm has yielded six unique Boron Carbide structures in B12C3stoichiometry, three of them with negative formation energies. Their formation energies lie within a band of 166 meV/atom, so they can be formed together in any optimal high temperature synthesis of B12C3and they are thermodynamically stable at temperatures up to 660 K. This work is the first independent confirmation using structure search that B11Cp(CBC) is the ground state structure of B12C3stoichiometry. New structures like the 14-atom-cage and the supercell (B11Cp)(B10Cpe 2)(CBC)(CBB) have also emerged in the structure search. Five structures have base-centered monoclinic symmetry and the supercell has triclinic symmetry, implying that the determination of monoclinic symmetry in B12C3by experimental measurements is an option for further inquiry. The mechanical stability of these systems are established through the analysis of their elastic constants and their dynamical stability from the phonon data. The high value of Bulk modulus (?250 GPa) indicates their high hardness and the B/G value confirms their brittle nature. The electronic structure shows that they are semiconductors with a significant reduction in the band gap when the structure does not contain the CBC chain. The curve fitting of the cumulative IR spectrum against the experimental spectrum implies that the presence of B11Cp(CBC) in the ground state composition could mostly be through structures of larger unit cells. The hardness values of these systems estimated by using the semi-empirical model based on bond strength are in excellent agreement with the experimental values. For the four structures with chain the hardness values are close to the superhard regime (>40 GPa). © 2016 Elsevier B.V.Item Semiconducting B13C2 system: Structure search and DFT-based analysis(Institute of Physics, 2019) Pillai, H.G.; Madam, A.K.; Chandra, S.; Cheruvalath, V.M.DFT calculation on Boron Carbide in B13C2 stoichiometry using a 15-atom unit cell necessarily results in metallic ground state regardless of the crystal structure. This is because such a unit cell consists of odd number of electrons, and hence complete filling of the top most band(s) of nonzero occupancy is impossible. This is in contrast to the observed semiconducting nature. If the crystal structure of B13C2 is made of a 30-atom unit cell which cannot be reduced to a 15 atom cell, there is a possibility of obtaining either a metallic or a semiconducting state as such a cell consists of an even number of electrons. In this work the evolutionary algorithm based structure search using 30-atom unit cells has yielded a previously unreported semiconducting system of B13C2 with unique bonding pattern. The mechanical and dynamical stability of the system have been properly established through the computation of elastic constants and phonon spectra. Its bond lengths, elastic moduli, hardness and infrared spectrum are in good agreement with experimental data. ©2019 IOP Publishing Ltd.Item Enhanced photostability and optical nonlinearity of nickel and cobalt organometallic complexes(Elsevier B.V., 2019) Manjunatha, K.B.; Rajarao, R.; Poornesh, P.; Rudresha, B.J.; Umesh, G.; Badekai Ramachandra, B.R.Nonlinear optical and limiting properties of nickel, cobalt metal-organic complexes and ligand (L) {L = N,N?-o-phenylenebis (4-hyrdoxy-salicylideneimine)} were studied using Z-scan technique using Q-switched Nd: YAG laser with nanosecond pulses at 532 nm. The results reveal that metal complexes exhibit large negative nonlinear refractive index (n2) of the order of 10?11 esu. The metal complexes displays large nonlinearity than the ligand due to effective charge delocalization between metal ion and ligand. The magnitude of ground state absorption cross section is small compared to the effective excited-state absorption cross section implying the observed nonlinearity is due to reverse saturable absorption. Further, metal-organic complexes exhibit enhanced optical limiting behaviour at nanosecond laser pulses. © 2019 Elsevier B.V.Item Exploring the possibilities of double proton transfer in hydrazides: A theoretical approach(John Wiley and Sons Ltd vgorayska@wiley.com Southern Gate Chichester, West Sussex PO19 8SQ, 2019) Mohan, M.; Satyanarayan, M.N.; Trivedi, D.Hydrazides are known to exhibit keto-enol tautomerism upon photoexcitation. Theoretical aspects uncovering excited state intramolecular proton transfer (ESIPT) of N-acylsubstituted hydrazides with bithiophene core have been investigated. Geometrical aspects of the system are expected to undergo double proton translocation at its excited state. However, potential energy surface study for all the molecules reveals an impossible concurrent double proton translocation and to a greater extent dubious step-wise double proton translocation in the system. Potential energy scans reveal molecules possessing a lower forward barrier at its excited state in comparison with their ground state suggestive of possible excited state single proton transfer. Geometrical attributes and spectral analysis suggest the strengthening of intramolecular hydrogen bond (N?H???O) at its excited state, favoring single proton translocation. Theoretical estimation of electronic energy transition for all the conformers yields good correlation with the experimental figures with an energy overestimation <0.17 eV. © 2019 John Wiley & Sons, Ltd.Item Magnetic complexity, magnetodielectric effect and DFT calculations on correlation driven Gd2CoMnO6 insulator(Elsevier B.V., 2022) Prashanth, C.H.; Reddy, I.; Tarafder, K.; Chandrasekhar Kakarla, D.; Yang, H.D.; Adyam, V.; Jyothinagaram, K.In the family of Re2CoMnO6 manganite double perovskites, in contrast to parent La2CoMnO6 compound, Gd2CoMnO6 exhibits multiple magnetic transitions; ferromagnetic (FM) ordering, TC ∼ 112 K followed by AFM transition, TN ∼ 47 K, Gd spins ordering for T < 10 K and large isothermal entropy changes. A study of DC field-superimposed AC magnetic susceptibility measurements revealed the field-induced magnetic glassy behavior below TC and enhancement of FM correlations above TC. From the analysis of Almeida-Thouless behavior and dynamical power-law fit to frequency dependent AC susceptibility, Gd2CoMnO6 exhibits a volume spin glass-like nature below the freezing temperature, Tf ∼ 117.5 K. The isothermal field-dependent magnetic and dielectric permittivity data and temperature dependent Raman measurements (reported in ref. R. X. Silva et al., J, Appl. Phys. 114 194,102 (2013)) confirms the spin-phonon coupling induced magnetodielectric effect. Further, the ground-state electronic structure and magnetic properties of Gd2CoMnO6 are investigated using DFT + U formalism with Vienna Ab-initio Simulation Package (VASP) code and predicted the material to be a correlation-driven insulator. The correlation value of the Hubbard U parameter at the 4f-Gd elements changes the stability of the magnetic state from Ferri to FM spin alignment for Ueff ≥ 3 eV and is correlated to the experimentally observed field-induced transformation of the short-range-order FiM/spin-glass-like phase into the long-range ordered FM phase. © 2022Item Synthesis, optical, electrochemical, and computational investigation of new cyanopyridine-centered organic dyads(Elsevier B.V., 2023) Naik, P.; Pilicode, N.; Keremane, K.S.; Acharya, M.; Vasudeva Adhikari, A.V.Herein we report the molecular design, synthesis, and inclusive investigation of four novel di-anchored symmetric dyes (CP1-4) centered on electron deficient cyanopyridine scaffold as possible photosensitizers for DSSC application. These new chromogens (CP1-4) comprise a powerful electron-withdrawing cyanopyridine moiety linked with additional electron attracting functionalities such as cyanoacetic acid (CP1), 3-(carboxymethyl) rhodanine (CP2), 2,4,6-pyrimidinetrione (CP3), and 2,6-dihydroxy-2-mercaptopyrimidine (CP4), as effective acceptor/anchoring units via biphenyl donor units. Their in-depth optical and electrochemical behaviour were investigated to assess their suitability as photosensitizers. Further, the molecular modeling calculations were undertaken to understand their ground state properties and energy level potentials. The comprehensive studies revealed that they own all the requisites to performance as a potential photosensitizer for DSSC application. © 2023 Elsevier B.V.Item Low field-cooled induced large exchange bias effect and DFT calculations in ferromagnetic Sm2CoMnO6(Elsevier Ltd, 2024) Nayak, A.; Prashanth, C.H.; Bala, D.; Reddy, I.R.; Tarafder, K.; Adyam, V.; Jyothinagaram, K.In the present report, we study the large exchange bias effect in Sm2CoMnO6 (SCMO) polycrystalline samples synthesized with the presence of two crystallographic phases: ordered-phase (monoclinic; P21/n) and disordered-phase (orthorhombic; Pnma). X-ray photoelectron spectroscopy study revealed the presence of mixed valence states for Co (2+ & 3+) and Mn (4+ & 3+). M(T) data exhibits an inhomogeneous magnetic state with the presence of ferromagnetic ordering at TC ∼128 K due to the super-exchange interactions of Co2+-O2--Mn4+ and antiferromagnetic-like spin correlations for T < 50 K, attributed to Co3+-O2--Co3+, and Mn3+-O2--Mn3+ interactions. M(H) loop shift with a conventional exchange bias (EB) effect of 10 kOe for a field-cooled (HFC) of 10 kOe at 2 K was observed. Such a large value of the EB effect for low HFC in SCMO is comparable to that of large EB compounds, such as La1·5Sr0·5CoMnO6 and NiFe2O4/CoO nanocomposites. The zero-field cooled asymmetry in the M(H) loop is termed a spontaneous exchange bias effect (SEB) observed for T < 20 K. The systematic study of EB effects like HEB and MEB with T(K) and HFC was explained qualitatively by the presence of unidirectional anisotropy formed at the interface of inhomogeneous magnetic phases. Further, density functional theory (DFT) calculations validate the ferromagnetic ground state of SCMO with Co and Mn networks. Moreover, the semiconductor characteristics of SCMO are established with a band gap of 1.3 eV. © 2023