Reducing the optical band gap of polyvinyl alcohol (PVA) based nanocomposite

Optical properties of pure polyvinyl alcohol (PVA) and PVA based nanocomposite films have been investigated. The nano-composite samples were prepared by the well known solution cast method. The experimental results shows that the absorption and absorption coefficient parameters are greatly affected by variation of copper oxide (CuO) nanoparticles concentration. The absorption versus wavelength for the doped samples is exponential while the absorbance of pure PVA is sharply varied with wavelength. An obvious surface plasmonic resonance peaks for the nano-composite samples were appeared. The absorption edge was greatly shifted to lower energy for the PVA doped samples. It was observed that optical band gap of pure PVA is significantly reduced upon the addition of CuO nanoparticles. The increase of refractive index with increasing CuO concentration is an evidence for the formation of new energy states and thus decreasing the energy band gap of PVA. The increase of optical dielectric constant was observed upon the addition of CuO nanoparticles. The optical dielectric loss peaks are shifted to higher wavelength with increasing the CuO concentration. The optical conductivity is increased upon the addition of CuO nanoparticles. The dispersion region in the refractive index spectra are well obeyed the single oscillator of the Wemple-Didomenico model for all the samples.