Exploring the Influence of Sudan IV Azo Dye on the Structural, Optical, and Dispersion Characteristics of PVA/Su-IV Composites

Abstract Flexible polymeric film composites consisting of polyvinyl alcohol (PVA) and Sudan IV azo dye (Su-IV) were synthesized using a casting method. Despite the known optical properties of PVA and azo dyes individually, the combined effects of Su-IV doping in PVA on the material’s optical and nonlinear optical properties have not been thoroughly investigated. This study addresses this gap by exploring the interactions between PVA and Su-IV at various doping concentrations (0.1–0.8 wt%) and their subsequent impact on the material’s structural and optical characteristics. Fourier transform infrared (FTIR) spectroscopy was employed to identify distinct vibrational groups within the composites, revealing that the incorporation of Su-IV induced random deviations in most absorption intensities compared to pristine PVA. Notably, new peaks at 519 and 444 cm −1 emerged, intensifying with increasing Su-IV concentrations, indicating significant interactions between the composite constituents. The optical properties were analyzed through transmittance and reflectance measurements, which uncovered new absorption peaks at 518 and 357 nm in PVA/Su-IV composites. These peaks correspond to electronic energy transitions of 2.4 and 3.6 eV, respectively, and their intensities increased with higher Su-IV content. Additionally, the indirect and direct bandgaps were decreased as Su-IV concentrations increased. The refractive index (n) analysis showed typical dispersion behavior between 850 and 2500 nm, aligning with the Wemple-DiDomenico (WDD) model. Furthermore, the oscillator parameters were calculated. Also, the nonlinear optical susceptibility (χ (3) ) was boosted from 4.19 × 10 −6 for pure PVA to 3.60 × 10 −4 for the sample with 0.8 wt% Su-IV. The nonlinear refractive index (n 2 ) was also measured at 8.55 × 10 −2 for the doped sample. These findings demonstrate the potential of PVA/Su-IV composites for applications in nonlinear optics and photonics.