Browsing by Author "Chandra Mathpal, Mohan"

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    Defects induced enhancement of antifungal activities of Zn doped CuO nanostructures
    (2021) Kumar, Promod; Inwati, Gajendra Kumar; Chandra Mathpal, Mohan; Ghosh, Soumya; Roos, W. D.; Swart, H. C.
    CuO nanostructures doped with different concentration of Zn have been synthesized by a simple low-cost combustion method. The prepared samples have been tested by the various techniques such as X-ray diffraction (XRD), Transmission Electron Microscope (TEM), Optical absorption spectroscopy, Photoluminescence, and X-ray photoelectron spectroscopy (XPS). XRD confirmed the presence of the monoclinic phase of CuO along with an extra ZnO phase in the CuO:Zn. TEM results confirmed almost spherical - shaped nanoparticles as well as some irregular shaped NPs for pure CuO and Zn doped CuO with the average size from 24 to 55 nm. The change in morphology revealed a structural change in the CuO:Zn crystal due to different concentration of the Zn. The chemical study was done by XPS and the results were also correlated with XRD based results. The role of localized defects was compared and interpreted for the change in the luminescence spectral bands, micro-stains and oxidation states of the CuO:Zn for the different concentrations. CuO:Zn nanostructures demonstrated significant antifungal activities against two South African plant pathogens, Alternaria alternata CGJM3078 and Alternaria alternate CGJM3006, in comparison to pure CuO samples. The result showed that the pure and Zn doped CuO samples could be used as a good antifungal agent that could have an extensive applications in the agricultural and biotechnological industries.
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    Optical limiting applications of resonating plasmonic Au nanoparticles in a dielectric glass medium
    (2021) Kumar, Promod; Chandra Mathpal, Mohan; Jagannath, Gangareddy; Prakash, Jai; Maze, Jero-R; Roos, W. D.; Swart, H. C.
    Plasmonic nanostructures exhibiting high optical nonlinearities are widely used in the rapidly growing modern nanotechnology of nonlinear optics including biomedical applications due to their tunable plasmonic behavior. In this work, we investigate the nonlinear optical properties of uniformly distributed Au nanoparticles (NPs) embedded in pre-synthesized sodium-zinc borate glass by the well-known ion-exchange technique for optical limiting (OL) applications. Various techniques such as optical absorption spectroscopy, x-ray photoelectron spectroscopy, Transmission Electron Microscope (TEM), Photoluminescence, Time of Flight secondary mass spectroscopy and the Z scan technique were used for the characterization of these NPs. TEM confirmed spherically shaped Au NPs with varying sizes of up to 16 nm, in agreement with optical absorption spectroscopy. Nonlinear optical (NLO) properties of these Au NPs were investigated by using an open as well as close aperture Z scan technique which exhibited enhanced optical nonlinearities. The two-photon absorption (2PA) coefficients demonstrated an increasing trend while the OL threshold values demonstrated a decreasing trend as a function of heat treatment. The improved 2PA coefficients and decreased OL threshold values endorsed the Au NPs containing glasses as contending materials for the fabrication of promising optical limiters for the protection of eyes and other sensitive instruments from laser induced damages.