Strong Plasmon-Exciton Coupling in Ag-Conjugated Polymer Core-Shell Nanoparticles

Light-matter interactions at the nanoscale is a major prospect of nanophotonics. Tightly-bound Frenkel excitons in organic semiconductors are particularly interesting for coupling with light because of their stability at room-temperature, giving rise to exotic physics such as Bose-Einstein condensation and low-threshold lasing of exciton-polaritons. By exploiting the strong electromagnetic fields confined to the surface of metal nanoparticles, surface plasmons enable strong light-matter coupling within nanoconfined geometries. Thus, strong coupling between surface plasmons and organic excitons can serve as platforms for exploring room-temperature macroscopic quantum phenomena.

Typically, excitons with narrow resonances, such as laser dyes have been employed to achieve strong plasmon-exciton coupling. However, these dyes have limited applications for optoelectronic devices compared with conjugated polymers, which exhibit large chromophore densities and minimal self-quenching in the solid state. Here, we demonstrate that, despite their broad spectral linewidth, ultrastrong plasmon-exciton coupling can be achieved for Ag-conjugated polymer core-shell nanoparticles, with potential Rabi splitting energies of >1000 meV.