  We theoretically discuss how to tune the competition between Forster transfer
and spontaneous emission in a continuous and nondestructive fashion. The
proposed approach is especially suitable for delicate biological systems like
light harvesting complexes and fluorescent protein oligomers. We demonstrate
that the manipulation of the density of photonic states at the emission
frequency of the energy donor results in a change of the quantum efficiencies
of the competing energy transfer and spontaneous emission processes. This
change will be manifested in a modification of the donor and acceptor emission
intensities. Thus, by controlling the local density of photonic states Forster
coupled systems can be manipulated and analyzed without the need to physically
separate donor and acceptor chromophores for individual analysis, which is of
interest, for example, for oligomeric reef coral fluorescent proteins.
