  By studying the fluorescence and optical properties of a three-level system,
we propose a new point of view on the coherent control of these spectra. With
the definite phase difference between the fields of the air band and dielectric
band in photonic band gap (PBG) reservoirs, the spectra of spontaneous
emission, absorption, and dispersion exhibit the coherent property and quantum
interference effect. This coherent interference depending on the position of
the embedded atom and the width of band gap causes the coupling of the
free-space light and the PBG light to result in blue shift of spectra and the
appearance of dark lines and kinks. By coherently controlling the
position-dependent dispersion, we can tune the frequency of slow light.
