Resonance Energy Transfer and Purcell Effect in a Cu2O/Au Hybrid Optical Antenna

Light trapping in subwavelength structures is a fascinating effect inspiring innovative technologies for solar energy harvesting, such as photocatalysis and photovoltaics. In these applications, energy trapped in an excited Mie mode must be efficiently converted to and transported by charge carriers. To this end, resonance energy transfer (RET) is a beneficial mechanism circumventing the challenge of charge transport to electrodes. Here, 48–64 nm diameter Cu₂O nanospheres on Au are investigated by single-particle light scattering and fluorescence spectroscopies. Modeling such a hybrid Cu₂O/Au optical antenna (OA) as an oscillator, where RET from the excited hybrid Mie mode to Au film is described as a damping channel (in addition to scattering and absorption), we measure a RET probability of 70 ± 9% for 532 nm excitation. The OA also mediates RET in the reverse direction, from an excited electron-hole pair in Au to the resonator mode, followed by photon emission (scattering) that enhances fluorescence quantum yield of Au up to 1.3 × 10⁵ times. This giant Purcell enhancement is attributed to strong concentration of the photon states around the Cu₂O/Au interface which spatially overlap with the emitter (coupled Au volume) along with low absorption and scattering damping in Cu₂O particles (i.e., dipole-forbidden gap and smaller particle size).