If the modal density available to an excited atom is varied on the time scale of its lifetime, then we can expect the natural process of spontaneous emission (SE) to become dynamically manipulable. We consider various experimental possibilities and focus on an atom embedded in a photonic crystal designed to have a band edge in the vicinity of the frequency of the emitted light. Specifically, we calculate the rate of SE by erbium ions (radiating at the wavelength 1.54 lm) implanted in a one-dimensional silicon/silica photonic crystal. The semiconductor layers are assumed to be strongly doped; by tuning the impurity density the free carrier concentration changes and the photonic bands shift. As a result, the SE rate exhibits significant dependency on the level of charge injection.