Flexible PVA/Ag₂S nanohybrid films as dual-functional materials for UV shielding and nonlinear optical applications

The present study examines the optical, structural, morphological and nonlinear optical (NLO) properties of polyvinyl alcohol (PVA) and silver sulfide (Ag₂S) nanocomposites for UV shielding and optical limiting applications. Herein, the solution casting method is employed to synthesize flexible, free-standing films of pure PVA and PVA/Ag₂S nanocomposites containing 0.5, 1, and 3 wt% Ag₂S nanoparticles (NPs). Besides, an in-depth analysis was performed for the synthesized films using various advanced characterizations techniques. In that, the X-ray diffraction (XRD) study confirmed the semi-crystalline structure of both pure PVA and PVA/Ag₂S nanocomposites. The Fourier transform infrared (FTIR) spectroscopy revealed the functional groups corresponding to PVA and vibrational modes resulting from the interaction between PVA and Ag₂S. The surface micrograph of the synthesized samples obtained using a field-emission scanning electron microscopy (FESEM) confirmed the formation of composite films with spherical Ag₂S nanostructures. In addition, UV–visible spectroscopy was employed to analyze the wavelength-dependent changes in absorbance, transmittance, optical bandgap, and Urbach energy of the samples. For Ag₂S incorporated PVA, the absorbance in the UV region (200–400 nm) has drastically increased, while retaining its transmittance in the visible range, making it suitable for UV-shielding applications. Furthermore, the incorporation of Ag₂S (0–3%) into PVA results in a narrowing of the bandgap (from 5.51 to 3.11 eV) and an increase in the Urbach energy (from 0.506 to 0.915 eV). Z-scan technique using a continuous wave (CW) laser source (λ = 532 nm) was used to study the NLO properties. The incorporation of Ag₂S NPs led to enhanced nonlinear absorption coefficient and susceptibility, with reduced optical limiting thresholds.