Effect of TiO2/ZnO nanofillers on structural, optical and nonlinear optical properties of PVA

Polyvinyl alcohol (PVA)/(x)Titanium dioxide (TiO2) (15-x) Zinc oxide (ZnO) nanocomposites for x = 0, 1, 5, 7.5, 10, 14 and 15 wt% concentration was prepared using solution casting method with the help of an ultrasonicator. The XRD spectra of films validate the formation of nanocomposites, as evidenced by the presence of peaks corresponding to both PVA and TiO2/ZnO nanoparticles. FTIR spectroscopy reveals the formulation of complexes between the PVA main chain and nano fillers. The homogeneous distribution of nano fillers in PVA nanocomposites was observed using SEM and EDAX. The optical studies conducted using an ultraviolet-visible spectrometer reveals that PVA/(x)TiO2(15-x) ZnO shows minimum energy gap of 2.66 eV at x = 15 wt%. The photoluminescence measurements carried out at an excitation wavelength of 370 nm using spectrophotometer exhibits unique strong emission band at 680 nm in the visible region for all the films. The open aperture (OA) Zscan traces of PVA filled TiO2-ZnO nanocomposites at various filling levels were explored by means of Z-scan technique with DPSS continuous wave laser at 532 nm wavelength and 200 mW output power reveals that the absorption coefficient (beta) of PVA nanofilms rises from 3.19 x 10- 5 cm/W (for pure) to 1.17 x 10-3 cm/W (for x = 14 wt %) with rise in filling level. The closed-aperture (CA) z-scan analysis gives the nature of third order nonlinear refractive index (NRI) (n2) of PVA nanofilms. The value of nonlinear refractive index (NRI) increases from -1.57 x 10-9cm2/W (pure PVA) to -3.24 x 10-8 cm2/W for x = 14 wt% filling level. The observed enhancement in Nonlinear absorption (NLA) coefficient (beta), NRI (n2) and third order nonlinear susceptibility (chi 3) of prepared nanocomposites is due to added nanofillers to the PVA matrix. The improved third order nonlinear optical properties make these PVA nanocomposites as good candidates for optical switching device and optoelectronic device applications.