Funneling of Molecular Electronic Energy through Surface Lattice Resonances

Hybrid plasmonic-photonic modes associated with lattices of plasmonic nanoparticles show high quality factors, making them suitable for widespread applications requiring enhanced light-matter interaction at high spectral selectivity. One such application is resonance energy transfer from donor to acceptor fluorophores. In this paper, we report a simple and practical theory of lattice plasmon mediated resonant energy transfer based on the coupled dipole approximation of electrodynamics. A matrix formalism is developed to obtain induced dipoles resulting from energy transfer for a finite array with multiple donors. The theory can be further extended to an infinite array and for polarizable donors. Achieving enhanced energy transfer as a result of surface lattice resonance (SLR) excitation is demonstrated, but the wavelength of peak energy transfer can be red-shifted from that for the peak extinction when the emitters are not strongly coupled to the SLRs. In addition, a wavelength dependent power law dependence of the energy transfer rate on donor-acceptor separation is found, with the smallest exponent occurring at the wavelength that enables the most significant energy transfer. Importantly, energy transfer is still significant (few percent) over distances of hundreds of microns. The optimum energy transfer enhancement is over 10⁴ for linear arrays, so even if the donor-acceptor separation is hundreds of microns, the net energy transfer rate can be larger than that for much smaller separations (<1 μm) in the absence of the array. We also find that energy transfer is robust for structural deviations from the perfectly periodic lattice condition, and for stacked arrays. This work demonstrates practical realization of long-distance energy transfer in solid-state devices using the array as a mediator.