The effective medium approach was applied to a dielectric slab between one-
dimensional photonic crystals and the dispersion curves together with the f
ield amplitudes were determined. The probability amplitude and the spontane
ous emission spectrum were investigated for a two-level atom immersed in th
e region between the photonic crystals. The spontaneous emission rate was c
alculated numerically and an interesting feature is that this rate is zero
for certain slab thicknesses. The probability amplitude and the spontaneous
spectrum show peaks and dips when the mode frequency approaches the photon
ic gap regions.