Tuning Near-Field Interactions Using the Bright and Dark States of a Quantum Dot

We demonstrate that the cycling between internal states of quantum dots during fluorescence blinking can be used to tune the near-field coupling with a sharp tip. In particular, the balance between tip-induced field enhancement and energy transfer depends explicitly on the intrinsic quantum yield of the quantum dot. Our measurements show that for internal states with low quantum yield, energy transfer is strongly suppressed in favor of field enhancement, and explicitly demonstrate that suppressed blinking of quantum dots near metal surfaces is due to fast energy transfer.