Abstract A phase-shift method was used to study the mercury-photosensitized luminescence of NH 3 and ND 3. The phase angles of the sensitized luminescence and the Hg( 3P 0 absorption relative to the resonance fluorescence at 253, nm were measured. The phase angle of the luminescence was found to vary with the wavelength measured. This result indicates that there are two kinds of emitting species. The phase angle of the short wavelength component of the luminescence was larger than that of Hg( 3P 0) absorption, which implies that the carrier of the short wavelength emission band is produced solely in a reaction of Hg( 3P 0) with ammonia. The lifetime of the stabilized complex was estimated from the phase difference between the short and the long wavelength components of the luminescence. It was 1.49 ± 0.04 μs for Hg-NH 3 * and 1.33 ± 0.06 μs for HgND 3 *.