As we know that a shell can be modeled as hybridization of a cavity and sphere. There is equation to find out the two different mode frequency of a metal shell if the dimension and bulk plasmon frequency is known.
When the structure is a core-shell, these two modes of hollow shell will again interact with Au sphere and provide different modes of core-shell structure.
The equation used to find out the hollow shell mode has a provision of a single bulk plasmon frequency. Whenever it comes to a core-shell structure, there are two bulk plasmon frequencies.
My question is what is the equation to find out the interaction of core and different modes of hollow shell?