<p>This study investigates the optical characteristics of CMC/PVP based bionanocomposites reinforced with carbon nanostructures, including graphene oxide (GO), multi-walled carbon nanotubes (MWCNTs), and their hybrid combinations. Four films, BNC0 (pristine CMC/PVP), BNC1 (GO), BNC2 (MWCNT), and BNC3 (GO/MWCNT), were fabricated via an environmentally friendly solution casting method and characterized using UV–Vis spectroscopy, FTIR, and SEM. SEM analyses revealed microscale heterogeneity arising from partial agglomeration, while the carbon fillers remained overall uniformly dispersed within the polymer matrix. FTIR confirmed functional group interactions among CMC, PVP, and the nanofillers, while UV–Vis measurements demonstrated enhanced optical absorption and a pronounced red shift in the absorption edge upon incorporation of GO and MWCNTs, particularly in the hybrid BNC3 film. The optical band-gap energy (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({E}_{g}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>E</mi> <mi>g</mi> </msub> </math></EquationSource> </InlineEquation>) was determined using Tauc, Absorbance Spectrum Fitting (ASF), Kubelka–Munk (K–M), and dielectric loss methods, all of which consistently indicated significant band-gap narrowing with increasing filler content due to the formation of localized states and improved charge transfer pathways. Urbach energy (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({E}_{u}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>E</mi> <mi>u</mi> </msub> </math></EquationSource> </InlineEquation>) calculations revealed broader band tails and increased structural disorder in the nanocomposites. Furthermore, the presence of carbon fillers markedly increased the refractive index (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(n\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>n</mi> </math></EquationSource> </InlineEquation>), dielectric constants (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({\varepsilon }_{r}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ε</mi> <mi>r</mi> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\({\varepsilon }_{i}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ε</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation>), and extinction coefficient (<InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(k\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>k</mi> </math></EquationSource> </InlineEquation>), confirming improved polarization, carrier mobility, and electromagnetic loss behavior. Overall, the combined incorporation of GO and MWCNTs improves the optical absorption and dielectric properties of CMC/PVP bionanocomposites, suggesting their potential for optoelectronic and photonic applications.</p>