Control of Spectral Shift of Plasmon Resonance of Ag-PVP Nanocomposite By Varying The PVP Shell Thickness In Core-Shell Structure

Abstract

Metal-polymer nanocomposite materials have interesting physical, chemical, and optical properties which were highly utilized in electronic, optical,and biomedical applications. Here, we have experimentally and theoretically studied the crucial role of polymer Polyvinylpyrrolidone (PVP) on the localized surface plasmon resonance (LSPR) spectra of silver (Ag) nanoparticles (NPs). In this work, we have synthesized PVP stabilized Ag NPs in Ethelene Glycol (EG) medium and observed a large blueshift (20 nm)of LSPR peak and tunable plasmonic properties of PVP coated Ag NPs by only varying the concentration of PVP. A reduction of Ag NP size from 13 nm to 5 nm with the increase in PVP concentration from 0.125 mM to 3 mM is seen. We found that the observed large blueshift of the LSPR bands with the varying in PVP concentration is not just due to the reduced Ag NP size but due to the combined effect of thickness of the PVP shell and radius of the Ag NP core. The polymer PVP used in the synthesis process of Ag NPs plays role of a surface modifier and forms a protective shell/layer surrounding the (core) particle. This is supported by the theoretical optical absorption data obtained from a modified effective medium theory. To accommodate such a large blueshift of the LSPR bands we have considered the Ag-PVP core-shell structure. The LSPR peak shift in the core-shell nanostructure is well accommodated by varying the effective shell thickness of PVP while taking the core size of Ag NPs as measured experimentally for each case. This clearly indicates that the observed large blueshift of SPR band of Ag NPs cannot be justified by considering the decrease in Ag NP size alone. It is also confirmed that the shell thickness of PVP plays a crucial role in explaining the blueshift of the SPR band of Ag NPs. This study can help to understand the optical response especially plasmonic properties of other metal NPs coated with organic polymers.