  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.
