Comprehensive investigation of linear and nonlinear optical properties and tunable band gaps in CS/PVP-GnP nanocomposites

Abstract The growing demand for low-cost and environmentally friendly polymer nanocomposites has intensified research efforts toward advanced functional materials. In this work, chitosan/polyvinylpyrrolidone (CS/PVP) nanocomposites reinforced with graphene nanoplatelets (GnP) were fabricated using a solution-based method and systematically characterized to evaluate their electrical and optical performance. The study focuses on electrical conductivity, optical band gap energy ( E g ), Urbach energy ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>u</mml:mi> </mml:mrow> </mml:msub> </mml:math> ), reflectance ( R ), refractive index ( n ), optical conductivity, and optical dielectric properties. To gain deeper insight into the dispersive and electronic behavior of the nanocomposites, the Wemple–DiDomenico (WD) model, the Spitzer–Fan model, and the Drude free-electron model were employed. In addition, the nonlinear optical (NLO) parameters, including optical susceptibility and nonlinear refractive indices, were analyzed. The results reveal significant enhancements in both linear and nonlinear optical properties with increasing GnP content, highlighting the strong structure–property relationships within the nanocomposite system. These findings demonstrate that CS/PVP-GnP nanocomposites are promising candidates for advanced applications in optoelectronics, energy storage, and photonic technologies.