  Strong modification of spontaneous emission of Eu3+ ions placed in close
vicinity to thin and thick gold and silver films was clearly demonstrated in a
microscope setup separately for electric and magnetic dipole transitions. We
have shown that the magnetic transition was very sensitive to the thickness of
the gold substrate and behaved distinctly different from the electric
transition. The observations were described theoretically based on the dyadic
Green's function approach for layered media and explained through modified
image models for the near and far-field emissions. We established that there
exists a "near-field event horizon", which demarcates the distance from the
metal at which the dipole emission is taken up exclusively in the near field.
