Investigation of the Absorption Edge and the Optical Bandgap of PVA/PVP-based Thin Films

The absorption edge, optical bandgaps, and optical losses of synthesized polyvinyl alcohol/polyvinylpyrrolidone-based polymeric composite films have been studied. The films were examined by different techniques, while absorbance measurements have been conducted to investigate the optical parameters. X-ray diffraction reveals that incorporation of acetic acid or hydrofluoric acid with the polymeric blend results in an increase in the amorphousness of the polymeric-based composites. FTIR analysis confirms the interaction between blend chains and the different additives. SEM reveals the smooth and homogenous surface morphology of all the studied films. The significant shift in the absorption edge of the films confirms the decrement of the optical bandgap of the composites. It was found that the allowed direct and indirect energy gap values, for all the films in this work are lower than many recently reported polyvinyl alcohol/polyvinylpyrrolidone-based films. Inclusion of 1% hydrofluoric acid to the polymeric blend results in the greatest reduction in both the allowed, and forbidden direct energy gaps, compared to other investigated films. Introducing 1% acetic acid to the polymeric blend results in the smallest allowed indirect energy gap, while the addition of 1% glycerol to the former composite results in the smallest forbidden indirect energy gap, among the other studied films. Furthermore, the films show low optical losses in the telecommunications range. This substantial modification in the optical parameters of the films enables the employing of such polymeric-based composites in different optical and optoelectronic applications.