Size-dependent optical properties of transparent, spin-coated polystyrene/ZnO nanocomposite films

Zinc oxide (ZnO) nanoparticles are synthesized using a simple chemical method at room temperature. A variation in molar concentration of the precursor, potassium hydroxide, from 0.25 to 0.01 mol L-1 is accompanied by a decrease in the average size of the nanoparticles. These nanoparticles are used for the preparation of polystyrene/ZnO nanocomposite films using the spin-coating technique. These films are found to be highly transparent throughout the visible region and absorb UV light in the region from 395 to 190 nm, almost covering the near and middle UV ranges (400 to 200 nm). This observation highlights the possible prospects of these films in UV shielding applications. The wavelength corresponding to the onset of UV absorption is found to be blue shifted with a decrease in size of the ZnO particles in the composite films due to confinement effects. The photoluminescence spectra of the composite films also change as a function of particle size. The emissions at longer wavelength due to defects and impurity-related states in ZnO are almost quenched as a result of surface modification by the polymer matrix. The observed band-gap enlargement with a decrease in size of the ZnO particles in the composite films is significant for band-gap engineering of nanoparticles for various applications. (C) 2011 Society of Chemical Industry