Structural, Optical, Dielectric and Nonlinear Properties of PVA/Na-Alg/ITO Nanocomposite Films

Flexible and optically active polymer nanocomposites have attracted significant attention for next-generation optoelectronic and photonic applications. In this study, PVA/Na-Alg/ITO nanocomposite films were successfully fabricated via a solution casting method, and the effect of indium tin oxide (ITO) nanoparticle incorporation (2–5 wt%) on their structural, optical, dielectric, and nonlinear optical properties was systematically investigated. X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and Raman analyses confirmed good miscibility between polyvinyl alcohol (PVA) and sodium alginate (Na-Alg), along with uniform dispersion of ITO nanoparticles with an average crystallite size of 21.7 nm. Morphological analysis revealed homogeneous films with minimal agglomeration. UV–visible spectroscopy showed a red shift in the absorption edge accompanied by a systematic reduction in optical band gap from 3.59 eV (pristine PVA) to 3.18 eV (5 wt% ITO), indicating enhanced electronic interactions and charge delocalization. The refractive index increased from 1.47 to 1.78, while the dispersion energy (Ed) improved from 8.28 eV to 12.17 eV with increasing ITO content, reflecting enhanced electronic polarizability. The dielectric constant (ε∞) also increased from 2.37 to 3.46, confirming strengthened interfacial polarization effects. Photoluminescence (PL) analysis revealed significant quenching of emission intensity with increasing ITO concentration, indicating efficient charge transfer and suppression of radiative recombination. Furthermore, the nonlinear refractive index (n₂) increased from 0.675 × 10⁻¹² to 4.83 × 10⁻¹², while the third-order nonlinear susceptibility (χ⁽³⁾) increased from 0.314 × 10⁻¹³ to 2.84 × 10⁻¹³ (esu) as ITO content increased from 0 to 5 wt%. These results demonstrate that controlled incorporation of ITO nanoparticles significantly enhances the structural disorder, optical tunability, dielectric response, and nonlinear optical performance of PVA/Na-Alg films. The developed nanocomposites show strong potential as environmentally friendly, flexible materials for advanced optoelectronic, photonic, and nonlinear optical device applications.