Insights into optical band gap identification in polymer composite films based on PVA with enhanced optical properties: Structural and optical characteristics

In this study, poly(vinyl alcohol) (PVA) was integrated with various amounts of dibismuth trioxide (Bi2O3) to produce PVA:Bi2O3 composites using casting methodology. The influence of Bi2O3 filler loading on the structure of PVA was investigated through the XRD and FTIR approaches. The XRD and FTIR outputs revealed polymer/ filler interactions. For all the composite films, the transition of electrons from the filled valence band to empty conduction bands is a complicated subject in condensed matters. Band gap detection is discussed in the aspect of two models to identify the nature of electron transitions as an obscured topic in condensed matter physics. The application of Tauc's model was successful in determining the direct and indirect band gap energies. The band gap of PVA was 6.3 eV and reduced to 3.28 eV upon the insertion of 12 wt% of Bi2O3 filler. With the help of optical dielectric loss versus photon energy, the most probable exponent (y) value in Tauc's equation was fixed. The wavelength-dependent on the real and imaginary parts of the optical dielectric function and the W-D model were utilized to determine the fundamental parameters, including N/m*, epsilon infinity, z, mu opt, wp, popt, Ed, Eo and no. The N/m* is enhanced from 3.65 x 1055 m3/kg to 42.58 x 1055 m3/kg. The improvement of dispersion energy from 1.36 to 6.71 is evidence of amorphous enrichment in composite films. The W-D model uses the refractive indexes to estimate the optical band gap. The single oscillator parameter (Eo) determined from the W-D model is close enough to the band gap received from the Tauc model.