Optoelectronic properties of dye doped polymer based on PVA: Structural and UV–vis studies

Abstract

This study investigates the structural and optical modifications in polyvinyl alcohol (PVA) films doped with a natural dye extracted from Cosmos sulphureus (CSC). FTIR analysis confirms the presence of functional groups in the dye, including NH, OH, and CO, indicating strong intermolecular interactions with PVA and the plasticizer. The optical properties were examined using UV–vis spectroscopy, revealing a significant redshift in the absorption edge with increasing dye concentration. The optical bandgap decreased from 5.18 eV for pure PVA to 2.41 eV for PVA doped with 6 mL dye, while the Urbach energy increased from 0.35 eV to 0.39 eV, indicating enhanced structural disorder. The refractive index increased to 2.13, suggesting improved light confinement. The optical dielectric function was analyzed to assess surface and volume energy losses. At the same time, the Wemple-DiDomenico (W-D) model was applied to determine the effective oscillator energy (2.91 eV) and dispersion energy (1.13 eV). The nonlinear refractive index exhibited an increasing trend with dye concentration. These findings demonstrate that CSC dye significantly alters PVA's optical properties, making it a promising candidate for optoelectronic and photonic applications.