Effects of position and density distribution of atoms on spontaneous emission (SE) from excited two-level atoms in an anisotropic and two-band photonic crystal (PC) are investigated. By considering these atoms with a Gaussian distribution in the PC, which acts as a coherent photonic-band-gap reservoir, we find that a photon-atom bound state occurring in the single-band model becomes a decay state as the center of atomic distribution is moved from the void region toward the dielectric region. The strong coupling between the atom and electromagnetic (EM) modes from both the air and dielectric bands leads to one of the enhanced decay behaviors. This effect is position-dependent and is dominant for a narrow atomic density distribution. The other decay behavior comes from the collective emission through the tunnel processes of the localized photons, which is dominant for a wide atomic density distribution. Therefore, for the wider atomic distribution, the collective effect on SE is stronger than the position-dependent one. By tuning the position and atomic density distribution, we can thus control the fluorescence of atoms in PC systems effectively. (C) 2016 Elsevier B.V. All rights reserved.
