The luminescence emitted during mercury-sensitized photolysis of NH3 or ND3 arises from the reaction of the ammonia molecules with Hg(3P0) atoms formed during quenching of Hg(3P1). The rates of the reactions with Hg(3P0) have been measured by a rotating sector method. Quantum efficiencies of luminescence have been determined by comparing the integrated intensities of the emission bands with the intensity of scattered mercury radiation in the absence of quencher; the values are 0.70±0.14 for NH3 and 1.05±0.20 for ND3. The emitting species has been identified as a charge-transfer complex of ammonia and Hg(3P0).