Enhanced linear and nonlinear optical properties of thermally stable ZnO/poly(styrene)-poly(methyl methacrylate) nanocomposite films

摘要

Highly transparent and thermally stable zinc oxide (ZnO)/poly(styrene)-poly(methyl methacrylate) (PS-PMMA) nanocomposite films have been deposited on glass substrates, from the ZnO incorporated (PS-PMMA) solutions in toluene, using spin coating technique. A chemical route at room temperature is used to synthesize the ZnO nanopartides. Transmission electron microscope and high-resolution transmission electron microscope images show that the ZnO nanopartides are of size around 10 nm. The composite films have been characterized by X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, Ultraviolet-visible-Near Infrared (UV-vis-NIR) spectroscopy, Thermo-gravimetric analysis, photoluminescence (PL) spectroscopy and Z-scan technique. From the UV-vis-NIR spectra it is observed that the ZnO/PS-PMMA nanocomposite films with 10 wt.% ZnO content exhibit excellent shielding property in the UV region and, high transparency in the visible region. The PL spectrum of the composite films is different from that of ZnO and PS-PMMA blend and exhibits an exdtonic emission peak at -375 nm. The optical absorptive nonlinearity in the nanocomposite films is investigated using open aperture Z-scan technique. The results indicate optical limiting type nonlinearity in the films due to two photon absorption. A transmittance minimum of around 0.25 has been observed in the ZnO/PS-PMMA nanocomposite films which is much lower compared to that in ZnO/PMMA and ZnO/PS nanocomposite films. The ZnO/PS-PMMA nanocomposite films also show a self-defocusing type negative nonlinear refraction in closed aperture Z-scan experiment. These nanocomposite films extend ample scope of applications as excellent optical limiters and efficient UV protectors.