PACS 71.55. Ht, 78.55.Hx Manganese (Mn)-doped GaS single crystals were grown by the Bridgman technique. Radiative recombination mechanisms have been investigated using photoluminescence (PL) measurement. The PL spectrum (at 77 K) related to the impurity level is dominated by the new emission band at 2.002 eV. The temperature dependences of the PL intensity, peak energy, and full width at half-maximum are characterized by the recombination mechanism of the configurational coordinate model. It was found that the 2.002 eV emission band is related to the acceptor -vacancy complex center. Moreover, the concentration of the defect is very high in the Mn-doped GaS.