Department of Physics

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Physics

An addition of chiral dopant to two achiral smectic liquid crystals from a homologous series, by varying weight percentages with known low values of layer shrinkage, leads to chiral smectic-C* phase with a finite value of the spontaneous polarisation. The electro-optical response arising from changes in the induced apparent tilt angle brought about by a weak electric field in the SmA* phase gives rise to power law dependency on the reduced temperature. The critical exponent γ of the power law depends on the dopant concentration but its value is found to be greater than the typical value of 1.32. This implies that the short-range correlation extends from two dimensions to three dimensions in these materials in the SmA phase. The layer thickness of smectic layers in the guest–host system remains unaltered up to the 15 wt % addition of the chiral dopant to two achiral smectics. The system thus retains the low layer shrinkage of the achiral smectic as evidenced by measurements of the layer thickness from X-ray scattering and thickness measurements from optical interferometry. Results on the optical birefringence and the apparent tilt angle lead us to the conclusion of having successfully obtained chiral smectic materials for devices with de Vries characteristics by chiral doping. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

School of Advanced Sciences

Chennai Campus

World University root node

Liquid Crystals

The effect of chiral doping in achiral smectic liquid crystals on the de Vries characteristics: smectic layer thickness, electro-optics and birefringence

We study a simple left-right symmetric extension of the Zee model for neutrino mass generation. An extra SU(2)L/R singlet charged scalar helps in generating a loop-induced Majorana mass for neutrinos in this model. The right-handed neutrinos in this case are very light of the order of a few electron volts to a few mega-electron-volts, which makes this scenario quite different from other left-right symmetric models. We have analyzed the scalar potential and Higgs spectrum in detail, which also play an important role for the neutrino phenomenology. We identified the parameter regions in the model which satisfy the experimentally observed neutrino masses and mixings along with other experimental constraints. We then studied the collider signatures of the charged scalar at e+e- colliders with different benchmark points. It is possible to get a huge enhancement in the production cross section of the charged scalar at a lepton collider compared to the hadron colliders, resulting in a much stronger signal, which can be easily observed at the upcoming International Linear Collider or Compact Linear Collider experiments. © 2018 authors. Published by the American Physical Society.

Fulltext

Physical Review D

Neutrino and collider implications of a left-right extended Zee model

Bulk single crystals of Imidazolium adipate (IA) were grown by solution growth method at 35 °C temperature. The solubility measurement of the material was carried out. FT-IR spectral analysis confirms the functional groups of the IA compound. Linear and nonlinear optical properties of the crystal were analyzed by UV-Vis-NIR transmittance and SHG studies. The high transparency with wide band gap is useful for optoelectronic applications are indicated. The SHG efficiency was higher than KDP. Vickers hardness study confirmed that the crystal was soft nature. Thermal stability of the material is up to 80 °C and the electrical study was carried out. © 2019, © 2019 Taylor & Francis Group, LLC.

Molecular Crystals and Liquid Crystals

Growth and characterization of Imidazolium adipate (IA) single crystal

An organic nonlinear optical material, guanidinium tosylate was synthesized adopting slow evaporation method and the crystals were harvested from aqueous methanolic medium with dimensions 13 × 9 × 3 mm3. Constitution of crystalline material was confirmed by single crystal X-ray diffraction study. The title compound crystallizes in the monoclinic crystal system with space group P21/c. The UV–vis–NIR spectral study of the grown crystal exhibits high transparency of 80% in the entire visible region with lower cut-off wavelength at 282 nm. Optimized molecular geometry of the grown crystal was obtained using density functional theory (DFT) and the frontier energy gaps calculated from the DFT aids to understand the charge transfer taking place in the molecule. The dielectric properties were studied as a function of temperature and frequency to find the charge distribution within the crystal. The titular compound is thermally stable up to 230 °C assessed by thermogravimetric and differential thermal analysis. Anisotropy in the mechanical behavior was observed while measuring for individual planes. The laser induced surface damage threshold of the grown crystal was measured to be 0.344 GW/cm2 for 1064 nm Nd:YAG laser radiation. Z-scan technique confirms the third-order nonlinear optical property with the ascertained nonlinear refractive index (n2), nonlinear absorption coefficient (β) and third order nonlinear susceptibility (χ(3)). Optical limiting study divulges that the transmitted output power step-up linearly with the increase of the input power at lower power realms and saturates from the threshold 24.95 mW/cm2 and amplitude 0.23 mW/cm2. © 2017 Elsevier Ltd

Optics & Laser Technology

Synthesis, growth, structural modeling and physio-chemical properties of a charge transfer molecule: Guanidinium tosylate

Third-order nonlinearity of monoclinic and orthorhombic phase of CuNb2O6 is studied in low power regime of 532 nm by Z-scan technique. In open aperture, monoclinic CuNb2O6 possess stronger saturable absorption due to the distorted structure arising from unequal arrangement of copper atoms. Closed aperture exposes the self-defocusing nature and orthorhombic phase exhibits stronger nonlinear refraction. Variation in third-order NLO coefficient due to change in phase and morphology of CuNb2O6 confirms the influence of sintering temperature and time. Microrod monoclinic CuNb2O6 possess maximum nonlinear absorption coefficient (6.47 × 10−3 cm/W) and pure orthorhombic CuNb2O6 attains maximum nonlinear refractive index (5.13 × 10−8 cm2/W) along with higher third-order nonlinear optical susceptibility (1.91 × 10−6 esu). Higher thermal nonlinearity resulted in stronger optical limiting action with pure orthorhombic CuNb2O6 (5.16 mW, 1.26 mW) compared to other phases. For understanding the material suitability for laser safety device, nonlinearity and limiting action of CuNb2O6 thin films were demonstrated. Earlier formation of monoclinic phase with morphology change (700 °C) and transition of monoclinic rich mixed orthorhombic phase to pure orthorhombic phase (900 °C) with increase in sintering time (3–12 h) was confirmed by XRD, FTIR and SEM analysis. Thus orthorhombic CuNb2O6 material with stronger self-defocusing and optical limiting action makes it more preference than monoclinic CuNb2O6 for third-order NLO applications. © 2018 Elsevier Ltd

Third order nonlinear optical properties of monoclinic and orthorhombic CuNb2O6 under CW laser illumination

By simple hydrothermal method, nanorods of barium boate were successfully loaded on reduced graphene oxide sheets. Powder XRD confirms the incorporation of barium borate (2θ = 29°, (202)) along with the transition of graphene oxide (2θ = 12°, (001)) into reduced graphene oxide (2θ = 25°, (002)). In the FTIR spectra, presence of characteristic absorption peaks of rGO (1572 and 2928 cm−1) and barium borate (510, 760 and 856 cm−1) further evidences the formation of BBO:rGO nanocomposite. FESEM images potray the existence of graphene sheets as thin layers and growth of barium borate as nanorods on the sheets of reduced graphene oxide. Ground state absorption studies reveal the hypsochromic shift in the absorption maxima of the graphene layers due to reduction of graphene oxide and hypochromic shift in the absorbance intensity due to the inclusion of highly transparent barium bortae. The photoluminescence of BBO:rGO shows maximum emission in the UV region arising from the direct transitions involving the valence band and conduction band in the band gap region. Z-scan technique using CW diode pumped Nd:YAG laser (532 nm, 50 mW) exposes that both nanocomposite and individual counterpart possess saturable absorption and self-defocusing behavior. Third-order nonlinear optical coefficients of BBO:rGO nanocomposite is found to be higher than bare graphene oxide. In particular the nonlinear refractive index of nanocomposite is almost four times higher than GO which resulted in superior optical power limiting action. Strong nonlinear refraction (self-defocusing) and lower onset limiting thershold makes the BBO:rGO nanocomposite preferable candidate for laser safety devices. © 2017 Elsevier B.V.

Optical Materials

Barium borate nanorod decorated reduced graphene oxide for optical power limiting applications

Cobalt substituted La2CuO4/LaCoO3 perovskite nanocomposites were prepared using a microwave combustion method.

VIT Unitversity

New Journal of Chemistry

Co2+ substituted La2CuO4/LaCoO3 perovskite nanocomposites: synthesis, properties and heterogeneous catalytic performance

Organic crystal of 2-aminopyridinium diphenylacetate diphenylaetic acid with dimensions 22 × 13 × 11 mm3 was grown by slow cooling technique. The structural confirmation has been done using single crystal X-ray diffraction study. The title compound crystallizes in the monoclinic crystal system with noncentrosymmetric space group P21. The C-H-O, N-H-O type of packing for the title compound has been reported. Optical transmittance shows a wide transparency in the visible region with lower cutoff wavelength at 349 nm. The four independent tensor coefficients of dielectric permittivity were found to be ε11 = 12.16, ε22 = 10.68, ε33 = 11.90 and ε13 = −4.24 from the dielectric measurements. The thermal stability of the 2APD compound was found to be 128˚C assessed by TG-DTA analyses. The particle size SHG of the 2APD reveals that it is a phase-matchable NLO crystal. © 2018

Computer Science

School of Computer Science and Engineering

Department of Multimedia

School of Design

Vellore Campus

Journal of Crystal Growth

Crystal engineering, structural and optical properties of 2-aminopyridinium diphenylacetate diphenylacetic acid crystal

A new organic nonlinear optical material, imidazolium diphenylacetate diphenylacetic acid, with excellent structural characterization and nonlinear optical activity has been reported.

Crystal structure, molecular packing, FMO, NBO, nonlinear optical and optical limiting properties of an organic imidazolium diphenylacetate diphenylacetic acid single crystal

Single crystals of L-Glutamic acid hydrochloride (LGHCl) were grown by slow evaporation solution technique and good crystalline perfection was confirmed by Powder X-ray diffraction studies. The complete vibrational studies of the compound were analyzed by FT-IR, FT-Raman and UV–visible spectra combined with Normal Coordinate Analysis (NCA) following the scaled quantum mechanical force field methodology and density functional theory (DFT). Twisted Intramolecular Charge Transfer (ICT) occurs due to the presence of strong ionic intra-molecular N[sbnd]H⋯O hydrogen bonding was confirmed by Hirshfeld Surface analysis. The existence of intermolecular N[sbnd]H⋯Cl hydrogen bonds due to the interaction between the lone pair of oxygen with the antibonding orbital was established by NBO analysis. The Z-scan result indicated that the title molecule exhibits saturable absorption behavior. The attractive third-order nonlinear properties suggest that LGHCl can be a promising candidate for the design and development devices for optical limiting applications. LGHCL exhibits distinct emission in the blue region of the fluorescence lifetime which proves to be a potential candidate for blue- Organic light-emitting diodes (OLEDs) fabrication. © 2017 Elsevier B.V.

VIT School for Agricultural Innovations and Advanced Learning

Journal of Molecular Structure

Twisted intramolecular charge transfer investigation of semi organic l -Glutamic acid hydrochloride single crystal for organic light-emitting and optical limiting applications