Optical properties of NaI doped polyvinyl alcohol films

Abstract

The optical characteristics of polyvinyl alcohol (PVA) doped with different concentrations (0, 1, 2, 3 and 4 wt%) of NaI nanocrystalline powders were studied. The films are prepared using solution casting technique, in order to investigate the effect of NaI additions on the optical properties of PVA host. The optical properties of samples are investigated by measuring optical absorption spectra in the wavelength range from 190 to 850 nm at 300 K using UV-Vis spectroscopy. The influence can be explained by the PVA matrix. The results show that Eg_opt. of the films decreases with increasing NaI contents. The absorbance, absorption coefficient, extinction coefficient, finesse coefficient, refraction index and reflectance of PVA doped with NaI increase with increasing of doping percentages except the transmittance. The real and imaginary parts of the dielectric constant and optical conductivity increases with increase sodium iodine concentration. The indirect optical band gaps for these undoped and doped PVA films were estimated to be about 5.05, 4.91, 4.79, 4.70 and 4.55 eV for indirect allowed transitions, whereas the indirect forbidden band gaps were determined as 4.91, 4.82, 4.75, 4.65 and 4.54 eV with increase sodium iodine contents, respectively. Absorption spectra peaks of the pure and doped films have shown an absorption band at 284.5 nm assigned to the monovalent state of sodium and iodine ions. The spectra peak points are between 204 and 259 nm for the calculated variables.

Keywords: Polyvinyl-alcohol, doping, optical properties, sodium iodine, optical energy gap, concentration.