Spontaneous emission in a three-level atom is investigated inside a dielectric cavity between asymmetrically photonic crystals. The photonic crystals are treated within the effective medium approach and the modes dispersions and field amplitudes are determined. The atomic probability amplitudes and spontaneous emission spectra are evaluated for different atomic and cavity parameters. The probability amplitudes show interference effects due to spontaneous emissions from the upper levels to the lower level. Interesting features arise for the variations of the probability amplitudes and spontaneous emission spectra with the variations of frequency near the photonic crystals including dark lines and multi-peaks.