Highly efficient FRET from a single nitrogen-vacancy center in nanodiamonds to a single organic molecule.

We show highly efficient fluorescence resonance energy transfer (FRET) between negatively charged nitrogen-vacancy (NV) centers in diamond as donor and dye molecules as acceptor, respectively. The energy transfer efficiency is 86% with particles of 20 nm in size. Calculated and experimentally measured energy transfer efficiencies are in excellent agreement. Owing to the small size of the nanocrystals and careful surface preparation, energy transfer between a single nitrogen-vacancy center and a single quencher was identified by the stepwise change of energy transfer efficiencies due to bleaching of single acceptor molecules. Our studies pave the way toward FRET-based scanning probe techniques using single NV donors.