Rabi Splitting in Photoluminescence Spectra of Hybrid System of Gold Nanorods and J-aggregates

One of the main objectives of nanophotonics research is the control of the light−matter interaction on the nanoscale. The coupling between plasmonic and excitonic resonances (plexitonic coupling) is of great interest for fundamental studies and for many practical applications. The interaction between plasmons and excitons strongly affects energy and electron-transfer pathways and, as a result, absorption and emission properties. For many applications the so-called strong coupling regime is especially attractive, which is produced when the rate of coherent energy exchange between the excitonic and plasmonic systems exceeds the rate of the losses in the system. In this regime the two new hybrid states are generated, both having features of light and matter. These new states are separated by an energy called Rabi splitting.

While observation of Rabi splitting in extinction or transmission spectra of plexitonic structures that combine metal nanoparticles and molecular systems has been reported in a number of publications, photoluminescence properties of a plexitonic hybrid system in strong coupling regime remained more elusive to experimental investigation.

In this work the interactions between localized plasmons in gold nanorods and excitons in supramolecular J-aggregates were experimentally and theoretically investigated.

The evolution of the two extinction and emission peaks separated by Rabi energy was followed as the plasmon energy was gradually detuned from the excitonic resonance. By this way, clear anticrossing behavior of the hybridized modes was demonstrated not only in the extinction but (for the first time) also in the photoluminescence spectra of this system. Both the extinction and photoluminescence results were found to be in good agreement with the theoretical predictions obtained for the model that assumes two interacting modes with a significant Rabi splitting of ∼200 meV. It turned out that the evolution of the photoluminescence line shape with increasing detuning depends on the illumination wavelength. This effect was attributed to an incoherent excitation given by decay processes in either the metallic rods or the J-aggregates.

Rabi splitting in absorption (right, bottom) and photoluminescence (right, top) spectra of hybrid system of gold nanorods and J-aggregates (left, bottom). The Scheme on the left (top) shows the formation of lower (LB) and upper (UB) bands as a result of exciton-plasmon interaction.