  Optical cavities, plasmonic structures, photonic band crystals, interfaces,
as well as, generally speaking, any photonic media with homogeneous or
spatially inhomogeneous dielectric permittivity (including metamaterials) have
local densities of photonic states, which are different from that in vacuum.
These modified density of states environments are known to control both the
rate and angular distribution of spontaneous emission. In the present study, we
ask the question whether the proximity to metallic and metamaterial surfaces
can affect other physical phenomena of fundamental and practical importance. We
show that the same substrates and the same nonlocal dielectric environments
that boost spontaneous emission, also inhibit F\"orster energy transfer between
donor and acceptor molecules doped into a thin polymeric film. This finding
correlates with the fact that in dielectric media, the rate of spontaneous
emission is proportional to the index of refraction n, while the rate of the
donor-acceptor energy transfer (in solid solutions with random distribution of
acceptors) is proportional to n^-1.5. This heuristic correspondence suggests
that other classical and quantum phenomena, which in regular dielectric media
depend on n, can also be controlled with custom-tailored metamaterials,
plasmonic structures, and cavities.
