Spontaneous emission near the edge of a photonic band gap

We study spontaneous emission near the edge of a photonic band gap. Instead of a simple exponential decay in the vacuum, spontaneous emission displays an oscillatory behavior. A single photon-atom bound dressed state exhibits a fractional steady-state atomic population on the excited state. For a three-level atom we evaluate the spectral splitting and subnatural linewidth of spontaneous emission. In the presence of N-1 unexcited atoms we show that the collective time scale factor is equal to N^φ, where {φ}=2/3 for an isotropic band gap and {φ}=1 or 2 for anisotropic two-dimensional or three-dimensional band edges, respectively.