Pure ZnO and ZnO–Bi2O3 nanocomposites with 5 wt% and 10 wt% of Bi2O3 content were synthesized using the co-precipitation method. Optical properties such as refractive index (n), extinction coefficient (k), bandgap (Eg), and Urbach energies, as well as the band structure, were determined by modeling the experimental transmittance and reflectance UV–Vis spectra. The deduced bandgap and Urbach energies for pure ZnO (3.758 eV) increase with the increase of the doping degree of Bi2O3 in ZnO–Bi2O3 nanocomposite films. X-ray diffraction and scanning electron microscopy (SEM) was used to study the structural and morphological properties of these nanocomposite films. Pure ZnO and nanocomposites with Bi2O3 exhibit crystalline domains with wurtzite hexagonal structures, and as the doping degree of Bi2O3 increases, the crystallite size decreases. Based on SEM micrographs, the ZnO nanoparticles (NPs) structure shows the presence of aggregation. Moreover, Bi2O3 NPs in the nanocomposite film led to the further aggregation in the form of large rods. The elemental and chemical properties of the nanocomposites were investigated using infrared and energy-dispersive X-ray spectroscopy. The charge transfer process in the studied system is between ZnO and Bi2O3 conduction bands. Density-functional theory (DFT) calculations were performed for ZnO, Bi2O3, and ZnO-Bi2O3 compounds to investigate structural, optical, and electronic properties, being in agreement with the experimental results. © 2021 Elsevier Ltd and Techna Group S.r.l.