Strong Coupling State on Plasmonic Lattice Structures Under Electrochemical Potential Control

Abstract

The collective oscillation of free electrons in the metal nanostructures induced by the visible light illumination is recognized as the localized surface plasmon (LSP). The coherent light energy exchange between excitons of molecules and LSP can modulate not only the absorption characteristic but also the individual energy decay. This reversible light energy exchange process between LSP and molecular exciton is called as the strong coupling regime. Although the strong coupling can allow use the light energy efficiently, the relative short lifetime of LSP due to the energy dissipation via the radiative damping limits the application. On the other hand, the surface lattice plasmon (SLR) mode which is excited on the two dimensionally arranged metal nanoparticles shows the longer excited lifetime because the diffractive light scattered from each particle is used for the excitation of the LSP at neighboring nanoparticle, resulting in the suppression of the scattering loss. As we demonstrated in our previous study, we have successfully achieved the fine electrochemical structure control method for obtaining the longest lifetime of the SLR mode. From these backgrounds, in this study, we have fabricated the Au lattice structure on a conductive glass and to support organic dye molecules on it to achieve the strong coupling regime. Through the extinction and fluorescence measurements, we have successfully observed the peak splitting which was originated from the formation of the strong coupling. In addition, by the combination of electrochemical method, we have confirmed our successful results for the reversible tuning of the coupling strength. From all experiments, we have successfully estimated the number of the molecules contributing to the strong coupling state.[1] H. Minamimoto et al., Phys. Chem. C 2018, 122, 14162.