Size dependent local field enhancement factor of CdSe based core@shell spherical nanoparticles

We investigated the size dependent local field enhancement factor (LFEF) of CdSe@Ag and CdSe@ZnSe@Ag core/shell spherical nanoparticles theoretically and numerically within the framework of quasi-static approximation. From the potential distributions in the core, shell(s), and host medium, and using the modified Drude-Sommerfeld model, we separately obtained the expressions for LFEF of core/shell and core/spacer/shell nanocomposites. By changing the sizes of each of the components of the nanocomposites in these expressions, we found that the LFEF of CdSe@Ag increases with a decrease in the size of the core. At the same time, the resonance peaks are red shifted in the inner interface and blue shifted in the outer interface of the shell. The result also reveals that whether the shell radius is kept constant or decreased, increasing the core size produces a lower field enhancement factor showing that the core size is a crucial parameter to change the field enhancement factor of the dielectric core and metal shell nanoparticle (NP). When the spacer (ZnSe) is placed between the core (CdSe) and the shell (Ag), the resonance peaks increased with increase in the size of the core which was not observed in the case of the two layered core/shell nanocomposites having the same core and shell sizes. We also found that placing the spacer and varying the sizes of the core, the spacer, and the shell show different effects on the LFEF of the nanocomposite. The possibility of obtaining size dependent LFEF by adjusting the sizes of nanoparticles makes these nanocomposites attractive for applications in nonlinear optics, photocatalysis, and optoelectronics.