  We report on an experimental technique to quantify the relative importance of
electric and magnetic dipole luminescence from a single nanosource in
structured environments. By attaching a $Eu^{3+}$-doped nanocrystal to a
near-field scanning optical microscope tip, we map the branching ratios
associated to two electric dipole and one magnetic dipole transitions in three
dimensions on a gold stripe. The relative weight of the electric and magnetic
radiative local density of states can be recovered quantitatively, based on a
multilevel model. This paves the way towards the full electric and magnetic
characterization of nanostructures for the control of luminescence at the
single emitter level.
