Simultaneously giant enhancement of Förster resonance energy transfer rate and efficiency based on plasmonic excitations

We present a first-principles calculation on the rate and efficiency of F\"orster resonance energy transfer (FRET) from a donor to an acceptor when they are located in the hotspots of nanoparticle clusters. Nonlocal effect has been considered by using a hydrodynamic model. It is found that FRET rate and efficiency can be enhanced simultaneously by more than 9 and 3 orders of magnitude, respectively. The physical origins for these phenomena have been disclosed. Two opposite phenomena, the energy transfer rate is independent or dependent of the local density of optical states (LDOS), have been observed in the same system under different conditions. These findings not only help us to understand the unresolved debate on how the FRET rate depends on the LDOS, but also provide a new way to realize ultrafast energy transfer process with ultrahigh efficiency.