Influence of KI salt concentration on the hydroxypropyl methylcellulose films: Optical study

Abstract

Herein the optical properties of Hydroxypropyl methylcellulose/Potassium iodide (HPMC/KI) composite films were determined. The casting technique was introduced to make HPMC/KI films with different KI salt concentrations (0.1–1) wt%. The absorbance model was used to determine parameters like absorption edge, refractive index, real and imaginary sections of the optical dielectric function, extinction coefficient, Urbach energy, band gap, and optical conductivity in the spectral range 200–800 nm. As shown by the study, KI salt doping affects the optical properties of HPMC. The absorption edge (Ee) was widely displaced towards a region of lower photonic energy. The direct and indirect optical bandwidth gaps were lowered from 5.6 to 2.56 eV and 5.86 to 2.5 eV for the 1 wt % HPMC/KI film, respectively. The optical dielectric loss method was effectively employed as an alternate method for estimating the optical band gap. In addition, Tauc's extrapolation method identified the kind of electronic transition. The variation of the optical energy band gap and optical dielectric constant (ε1) based on KI salt concentration was used to investigate the credibility of Penn's model. In KI salt-composite films, an increase in Urbach energy and optical conductivity was observed which may be evidence of a large shift from tail-to-tail and band-to-tail transitions. Meanwhile, X-ray diffraction (XRD) examination revealed that the KI salts damaged the HPMC polymer's crystalline phase. Lastly, the films were subjected to Fourier Transform Infrared Spectroscopy (FTIR). The considerable variation in transmittance and band change was observed for doped films in FTIR spectra.