Bismuth functionalized PVA film: field, plasmonic and pH effect on PVA originated broad photoluminescence

Abstract

Bismuth (Bi) NPs have been synthesized by Laser Ablation Synthesis in Solution (LASiS) at different pH in different aqueous solutions [viz. H₂O (H), H₂O + NaOH (HN), and H₂O + HCl (HC)]. The NPs in aqueous solution have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV-Vis-NIR techniques. The NPs are spherical, core shell type and hollow spheres in H, HN and HC, respectively. The vibrational features have been studied using Raman technique and correlated with different states of NPs (neutral NPs, ionized NPs, hollow NPs, core shell type NPs and NPs complex, etc.). The NPs were later dispersed in polyvinyl alcohol (PVA). The electronic spectra of PVA molecules along with different types of Bi NPs films have been studied at different excitation wavelengths (λ_exci = 240 nm, 270 nm, 300 nm and 360 nm). The sequences of optical sensitization in increasing order are NPs, core shell type NPs, and hollow spherical NPs. The enhanced emission is discussed in terms of plasmonic and field effects and is verified by lifetime measurements.