Long Range Enegry Transfer via Hybrid Plasmonic-Photonic Structures

Dipole-Dipole resonant coupling is a common mechanism for short-range (typically 1-10nm) energy transfer (ET). Surface plasmons (SP) may enhance ET and indeed, it was demonstrated that SP on opposite sides of a thin metallic film may extend the ET range by carrying the donor emission to the acceptor [1,2], when both are located close to the metal. We demonstrate that a metallic microcavity which couples plasmonic and photonic modes [3] can further extend the ET range, exceeding 100nm. Our structure, (shown schematically in Fig. 1a) supports cavity-confined photons as well as surface plasmons on the top metal-air interface. When the dispersion curves of the SP and cavity-photon cross, normal-mode splitting is observed (Fig. 1b) and around this point hybrid photonic-plasmonic modes form. These modes reside both outside and inside the cavity (as shown in Fig. 1a) and here their unique field distribution for mediating ET between a donor overlay (Fluorescein) to intra-cavity acceptor molecules (Rhodamine-B), weakly-coupled to the hybrid modes which are tuned to the donor emission (Fig. 1b, solid line) and the acceptor absorption (dashed line) by adjusting the cavity dimensions. Photoluminescence measurements (Fig. 1c), show an emission peak around 570nm for a cavity containing the acceptor alone (black curve) and at 523nm for the donor alone (blue). When both are present (red) we find a 3-4 fold emission enhancement. Measuring the excitation spectrum at the acceptor emission wavelength for the mixed sample, we find a clear peak at the donor absorption maximum. Without the donor this signal disappears, proving that ET indeed occurs. This innovative and flexible ET mechanism allows selecting any desired pair of molecules, even if the spectral overlap is small, and may find potential applications in photovoltaic devices, where energy should be collected and efficiently conveyed into the photovoltaic cell.

[1] P. Andrew et al., Science 290, 785 (2000).

[2] E. Collini et al., J. Am. Chem. Soc. 134, 10061 (2012).

[3] S. Chen et al., Nanoscale 5, 9129 (2013).

katrinakulov@gmail.com