Chrysanthemum-extracted natural dye for developing dye-doped solid PVA films with improved optical and optoelectronic properties

In this study, a green chemistry method was used to synthesize dye-doped polymer based on polyvinyl alcohol (PVA). Polymer films were subsequently fabricated using a casting process. This method is cost-effective and environmentally friendly. The dye was synthesized for 24 h via the combination of a purple chrysanthemum extract solution with distilled water and added to PVA in different concentrations. Then, UV–Vis and FTIR characterizations were conducted for both pure and dye-doped polymers. The FTIR spectra exhibit that the additive dye contains sufficient functional groups (O-H, C-H, C=O, C=C, and C-O) to react with those of the polymer. The optical properties of dye-doped polymer films, via UV–Vis spectroscopy, were rigorously studied. The doped samples show a larger refractive index of approximately n = 2.65 and notable dispersion due to varying doping concentrations on the polymer. The nonlinear optical properties were further investigated. With increasing dye concentration, the nonlinear refractive index n2 rose from 2.41 × 10–12 to 2.41 × 10–11. The band gap Eg is calculated by examining the absorption edge, which is quantitatively reduced from 5.1 eV to 2.8 eV upon increasing the concentration of dye in the PVA samples. The decline of the band gap indicates a pronounced increase in structural disorder, resulting in the formation of localized states and a subsequent reduction in Eg.