A Surprising Role of Ferromagnetic Ions in Poly(vinyl alcohol) Polymer Films as Novel Composites for Photo-Switches Applications

In this work, we synthesized PVA films via casting technique and used them as a container matrix for iron ions at different valence ratios. The influence of the ratio of the Fe³⁺/Fe²⁺ ions on the structural, spectroscopic, and optical characteristics of PVA films has been evaluated through analysis of FTIR and UV‒Vis, techniques data. The FTIR results indicated the substitution of iron ions in the polymer matrix at the expense of the OH groups. The optical transmission spectra demonstrated a complete blocking in a particular UV and visible (200–474 nm) spectrum for composites of PVA-Fe³⁺/Fe²⁺ films, which is excellent for photo-switches applications. Moreover, the obtained values of the optical energy gap E_g based on Tauc and ASF methods indicate fast transformation from insulating state 4.80 eV in pure PVA film to semiconducting state 2.35 eV for PVA-20% Fe³⁺/Fe²⁺ film. The prepared composites can be candidates for signal delay devices where the calculated values of refractive indices increase from 1.75 to 2.2 by increasing the Fe³⁺/Fe²⁺ ratio from 0 to 20%, respectively, and as a result, their optical density increases and the light speed decreases through them. The impact of the iron ions additives on the electrical and dielectric properties has been studied according to the data of the two probes method and LCR bridge. The electrical characteristics results showed a decrease in both dielectric and dielectric loss factors (\(\epsilon {\kern 1pt} '\) and \(\epsilon {\kern 1pt} ''\)) with increasing frequency. The matrix of PVA film host for Fe³⁺/Fe²⁺ with a ratio equal to unity displays the highest value of \(\epsilon {\kern 1pt} '\). The measured data of the I–V indicate the dominant ohmic behavior over a wide voltage range (0–400 V) due to a good transport of charge carriers through the prepared samples and the highest value of electrical current has been found through the PVA film sample with Fe³⁺/Fe²⁺ ratio equal to unity.