γ-Irradiated PVA/Ag nanocomposite films: Materials for optical applications

Abstract

Polyvinyl alcohol–silver (PVA/Ag) nanocomposites were prepared through in situ reduction of silver nitrate (AgNO3) within PVA hydrogel under continuous stirring at 60°C. The observed characteristic surface plasmon resonance band at around 425nm in the recorded UV–Visible absorption spectrum confirmed the formation of Ag nanoparticles embedded in a dielectric matrix. It was found that pure PVA exhibited indirect optical energy gap (Eg) of 4.92eV, which reduced to 4.57eV after embedding Ag nanoparticles, suggesting the formation of charge transport complexes (CTCs) between the localized highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy bands of PVA. On exposure to gamma (γ) radiations at a dose of 50kGy, the value of Eg was reduced further and found to be 3.72eV. The decrease in optical energy gap and the observed increase in refractive index (n) of PVA/Ag nanocomposites before and after gamma irradiation in comparison with pure PVA suggest the possibility of their use in optical device applications. The induced structural changes in PVA after the formation of embedded Ag nanoparticles and subsequently through gamma irradiation, were revealed through X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) spectroscopy, corroborating the observed changes in their optical behavior.