Plasmonic–Molecular Resonance Coupling: Plasmonic Splitting versus Energy Transfer

Plasmonic–molecular resonance coupling was systematically studied using quasistatic approximation, Mie theory, and rigorous finite-difference time-domain calculations. The results indicate that the two types of coupling behaviors, plasmonic splitting and energy transfer, which are commonly manifested in experiments as peak splitting and a quenching dip, respectively, can be unified by considering a Au nanocrystal core coated with dye molecules. The dye coating is treated as a dielectric shell with Lorentzian-type absorption. By varying the oscillator strength and molecular transition line width, either plasmonic splitting or a quenching dip can be observed on the scattering spectrum of the dye-coated Au nanocrystal. The effects of the thickness of the dye coating, the spacing between the dye shell and the Au core, the partial dye coating, and the Au core shape on the coupled spectral shape were also ascertained. Our results will be useful for further exploring new phenomena in plasmon-based light–matter interactions as well as for developing highly selective and sensitive detection devices on the basis of plasmonic–molecular resonance coupling.