  We discuss the spontaneous emission from a coherently prepared and microwave
driven doublet of potentially closely spaced excited states to a common ground
level. Multiple interference mechanisms are identified which may lead to
fluorescence inhibition in well-separated regions of the spectrum or act
jointly in cancelling the spontaneous emission. In addition to phase
independent quantum interferences due to combined absorptions and emissions of
driving field photons, we distinguish two competing phase dependent
interference mechanisms as means of controlling the fluorescence. The
indistinguishable quantum paths may involve the spontaneous emission from the
same state of the doublet, originating from the two different components of the
initial coherent superposition. Alternatively the paths involve a different
spontaneous photon from each of two decaying states, necessarily with the same
polarization. This makes these photons indistinguishable in principle within
the uncertainty of the two decay rates. The phase dependence arises for both
mechanisms because the interfering paths differ by an unequal number of
stimulated absorptions and emissions of the microwave field photons.
