Optical investigation of the effect of laser radiation on lignosulfonate–polyvinyl alcohol/nickel oxide nanocomposite membrane

In the present work, we used the solgel and ex situ casting techniques to synthesize a nanocomposite membrane (NCM) composed of lignosulfonate (LGS), polyvinyl alcohol (PVA), and nickel oxide (NiO) nanoparticles. Samples from the synthesized NCM were exposed to different laser fluences in the range 2–22 J/cm2. UV–vis spectroscopy and the CIE methodology were used to study the resultant effect of laser on the optical and color characteristics of the NCM. The increase of fluence up to 22 J/cm2 causes a drop in the optical bandgap (Eg) values from 5.88 to 5.56 eV when n = 1/2, associated with a rise in the refractive index. We attribute these changes to cross-linking that destroys the ordered regions and thus increases the amorphous phase. This cross-linking can lead to a more compacted structure of the LGS–PVA/NiO NCM. Additionally, the values of optical dielectric loss were calculated and plotted versus energy. The values of Eg attained from ɛ″ versus energy are nearby to those values attained by means of Tauc's relation when n = 1/2, indicating that the LGS–PVA/NiO NCM exhibited direct allowed transition. Furthermore, the CIE method was used to evaluate the color differences between the exposed NCMs and the pristine ones. We found that the value of color intensity is more than 5, suggesting permanent color changes.