Browsing by Author "Dhananjay Kumar Gaur"

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Highly enhanced fluorescence parameters in a dye-doped liquid crystalline compound
(Taylor and Francis Ltd., 2024) Shivangi Tripathi; Shikha Agarwal; Sadhna Tiwari; Dhananjay Kumar Gaur; Atul Srivastava; Rajiv Manohar
Fluorescent liquid crystalline compounds have been the focal point of research due to their rich applications in organic optoelectronics. Fluorescent dyes have also found great applications in the development of random lasers and non-linear optics. Other than that, materials with high fluorescence intensity and quantum yield have been very desirable for various electro-optical applications over the years. We have attempted to engineer a highly fluorescent nematic liquid crystalline compound (4′-pentyl-4-biphenylcarbonitrile/5CB) with high quantum yield by doping anthracene dye. We have obtained the desired increase in fluorescence intensity due to anthracene being fluorescent as well and a further significantly high quantum yield for higher concentrations of anthracene in the nematic compound. The reduction in non-emissive radiations and the increase in the concentration of fluorophores in the excited state can be held responsible for this increased quantum yield. Lifetime of the fluorophores has been found to increase with the increase in the dye concentration. The obtained results make the anthracene-doped 5CB compound highly desirable for various device applications. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
Investigation of dielectric and optical properties of pure and diamond nanoparticles dispersed nematic liquid-crystal PCH5
(Taylor and Francis Ltd., 2021) Dhananjay Kumar Gaur; Ayushi Rastogi; Harshita Trivedi; Avanish Singh Parmar; Rajiv Manohar; Shri Singh
In the present work, we have dispersed diamond nanoparticles (DNPs) in nematic liquid crystal 4-(Trans-4ʹ-n-Pentylcyclohexyl) Benzonitrile (PCH5) and studied the dielectric and optical properties of pure and DNPs dispersed nematic systems. We have investigated the effect of dispersion of DNPs (concentrations 0.5 and 1.0 wt%) in nematic liquid crystals (NLC) PCH5 on the dielectric permittivity, dielectric loss, dielectric anisotropy, photoluminescence, UV-Vis absorbance. It has been found that these properties are influenced by the dispersion of DNPs in nematic PCH5 system and applied electric field. Due to the dispersion of DNPs (1.0 wt% concentration) in PCH5, a significant decrease in the relative permittivity occurs. The relaxation peaks of dielectric loss shifts towards higher frequency side for NLC-DNPs composites. The dielectric anisotropy has been found to decrease with the dispersion of DNPs into pure NLC. The PL emission and UV-Vis absorbance for the dispersed systems have been decreased. An effort has been made to explain the observed results on the basis of interaction between nematic molecules and diamond NPs. The possible applications have also been suggested for the dispersed systems in this study. © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Investigation of dielectric, optical and zeta potential properties of pure and zinc ferrite nanoparticles dispersed nematic liquid crystal PCH5
(Springer Science and Business Media Deutschland GmbH, 2022) Dhananjay Kumar Gaur; Fanindra Pati Pandey; Ayushi Rastogi; Avanish Singh Parmar; Rajiv Manohar; Shri Singh
The present work reports the results on dielectric and optical properties, and zeta potential of pure and zinc ferrite magnetic nanoparticles (ZnFe2O4 NPs) dispersed nematic liquid crystals (NLC) 4-(trans-4'-n-pentylcyclohexyl) benzonitrile (PCH5). The ZnFe2O4 NPs of three different concentration 0.25, 0.5 and 1.0 wt% have been dispersed in host nematic. The effect of ZnFe2O4 NP dispersion in NLC PCH5 on dielectric permittivity, dielectric anisotropy, ac conductivity, photoluminescence, Raman spectra and zeta potential has been studied. It has been observed that these properties are influenced by the concentrations of NPs in host nematic and applied electric field. Significant decrease in dielectric permittivity and dielectric anisotropy due to the presence of NPs in host nematic matrix has been observed. For the NP concentrations of 0.25 and 0.5 wt% in PCH5, photoluminescence intensity is increased, but it is decreased for the 1.0 wt% concentration of NPs in host nematic matrix. The numerical values of zeta potential are decreased with the concentrations of NPs. This result provides useful information on the stability and aggregation dynamics of the dispersed systems. In the profile of Raman spectra, variation in intensities is found for different orientations. An effort has been made to explain the observed results on the basis of interaction between NPs and nematic molecules. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
Optical properties and zeta potential of polyvinyl pyrrolidone capped gold nanoparticles dispersed nematic liquid crystal mixture E7
(Elsevier B.V., 2023) Dhananjay Kumar Gaur; Kaushlendra Agrahari; Bhupendra Pratap Singh; Md Bayazeed Alam; Avanish Singh Parmar; Rajiv Manohar; Shri Singh
The effect of dispersion of polyvinyl pyrrolidone (PVP) capped gold nanoparticles in nematic mixture E7 on the optical properties (absorbance and photoluminescence, fluorescence life time and Raman imaging) and zeta potential is studied. The gold nanoparticles of 0.25, 0.5 and 1.0 wt% concentrations are dispersed into E7. It has been found that the absorbance and photoluminescence intensity of dispersed systems are increased and depend on the GNPs concentration. These increase correspond to the coupling between the radiation field (electromagnetic waves of the light source) and the GNPs low-energy phonons and constructive coupling of emissions between the E7 and GNPs, respectively. The change in the fluorescence lifetime of pristine and GNPs dispersed E7 systems has confirmed the energy transfer between E7 and GNPs molecules. The study of Raman spectrum shows the variations in the intensity of the Raman peaks with different orientations. Due to dispersion of GNPs in E7 the values of zeta potential are increased. This ensures the good stability of the dispersed systems. The conductivity of dispersed system has increased drastically. In conclusion, the dispersion of GNPs in host nematic mixture E7 has influenced significantly its properties, thereby making the dispersed material more promising for the potential applications. © 2023
Twist-Bend Nematic Phase: Role of Third-Order Legendre Polynomial Term in Chiral Interaction Potential
(Springer, 2020) Shubham Mishra; Dhananjay Kumar Gaur; Shri Singh
Using a mean-field theory, a twist-bend nematic (NTB) phase has been described. In addition to second-order Legendre polynomial term, the chiral interaction potential includes third-order Legendre polynomial term also. It considers the coupling between a nematic director and a pitch axis of the NTB phase. The distortion free energy, order parameter for twist-bend nematic, and orientational distribution function in equilibrium state have been calculated. Based on the free energy minimization, we obtain that the inclusion of third-order Legendre polynomial term in interaction energy makes NTB phase more stable. © 2020, Sociedade Brasileira de Física.