DOI: 10.5176/2301-3516_OPAP13.50
Authors: M. Sajimol Augustine, P.B. Anand, S. Jayalekshmi
Abstract:
Development of methods for the synthesis and stabilization of monodispersed semiconductor nanoparticles in transparent matrices is an interesting research area in experimental nanotechnology. The present work is an attempt to realize highly luminescent and transparent nanocomposite films of chitosan capped, manganese doped ZnS nanocrystals (ZnS:Mn) in polyvinyl alcohol (PVA). Both the chitosan capped ZnS:Mn and PVA are water soluble and hence transparent luminescent films of the nanocomposite, chitosan capped ZnS:Mn +PVA can be grown easily on both glass and flexible substrates using spin – coating technique. Though there are numerous publications related to ZnS:Mn nanocrystals, there are no reports on the growth and characterization of the chitosan capped ZnS:Mn/PVA nanocomposite films. The fact that chitosan capped ZnS:Mn luminescent nanocrystals can be synthesized using simple and cost effective chemical precipitation technique, projects the significance of the present work. From the X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies, the nanocrystalline nature and the size of the chitosan capped ZnS:Mn nanocrystals have been confirmed and the crystallite size is approximately 10 nm. The chemical composition of the chitosan capped ZnS:Mn nanocrystals has been established based on the energy dispersive X-ray (EDX) studies. Field emission scanning electron microscope (FESEM) image of the nanocomposite films shows the homogeneous dispersion of the nanocrystals in the polymer matrix. UV-Visible spectra in transmission mode show that these films are highly transparent throughout the visible region and absorb UV light in the wavelength region from 300 to200 nm. There is an absorption window of width around 100 nm where the UV absorption is close to 100{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465}. This aspect highlights the prospects of applications of these films as transparent UV protectors. One of the highlights of the present work is the realization of transparent and flexible UV-shielding films using the cost effective polymer nanocomposite, ZnS:Mn/PVA. The chitosan capping has the additional advantage of considerably reducing the inherent toxic nature of ZnS. These chitosan capped polymer nanocomposite films also show intense room temperature photoluminescence (PL) emission around 597 nm under UV excitation. The intensity of PL emission in chitosan capped ZnS:Mn/PVA nanocomposite films is significantly higher than that in uncapped films. Another highlight of the present investigations is the identification of these highly luminescent, transparent, and flexible nanocomposite films as possible bio-compatible materials for bio-imaging applications. These transparent nanocomposite films with strong orange luminescence can also be used for ink-jet printing invisible writings onto transparent substrates. Under excitation with UV light, the writings become visible by the luminescence of the nanocomposite material.
Keywords: chitosan capped nanocrystals, nanocomposite films, UV-shielding, photoluminescence
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