We investigate the spontaneous-emission properties of a two-level atom embedded in a three-dimensinal anaisotropic photonic crystal. In addition to the modified density of states, the atom is driven by a coherent intense lowfrequency field (LFF), which creates additional multihoton decay channels with the exchange of two low-frequency photons and one spontaneous photon during an atomic transition, Due to the ow frequency of the appliced field, the various transition pathways may interfere with each other and thus give rise to a modifeed system dynamics. We find that even if all the atomic(bare and induced) transition frequencies are in the conducting band of the photonic crystal, there still mya exist a photon-atom bound state in coexistence with propagating modes. the system also allows us to generate narrow linesin the spontaneous-emission spectrum. This spectrum is a funcion of the distance of the observer form the atom due to the band gap in the photonic crystal. The system properties depend on three characteristic frequencies, which are influenced by quantum interfernce effects. Thus these results can b attributed to a combination of interference and band-gap effects.