Effect of the dopant salt on the optical parameters of PVA:NaNO₃ solid polymer electrolyte

In this work we investigate the impact of the dopant salt on the optical constants of PVA:NaNO₃ composite system. Samples with various NaNO₃ dopant contents were prepared by casting technique using distilled water as a solvent. The refractive index (n), extinction coefficient (k), dielectric constants (ɛ _r and ɛ _i ) and complex optical conductivity (σ*) for the systems have been investigated. Through applying Tauc’s equation and Wemple–DiDomenico (W–D) model, the optical energy gap (E _g ) and Urbach tail energies (E _u ) were correlated and analyzed. The exponent value (n) in Tauc’s equation has been calculated numerically and it was utilized to understand the nature of electronic transitions. The change in the refractive index from 1.14 for pure PVA to 2.25 for 12 % doped PVA was noticed, indicating the presence of few interactions between photon and electrons. This doping effect has considerably increased the real dielectric constant from 1.30 for pure PVA to 5.10 for 12 % doped PVA. The results showed that dispersion region of refractive index obeyed the W–D model.