The incorporation of Hg atoms was carried out into liquid-encapsulated Czochralski GaAs by high-energy ion implantation. Hall effects measurements at room temperature and 2 K photoluminescence spectra revealed that rapid thermal annealing method is superior to furnace annealing method in view of electrical and optical activation. Activation rate of Hg acceptors as high as 30% was obtained. Optically activated Hg acceptor was found to produce at least six Hg-related shallow emissions in the vicinity of band edge. In addition to the conduction band to Hg acceptor transition, associated with moderately deep acceptor binding energy (52 meV) of Hg, the Hg majority acceptor is found to produce a neutral acceptor complex defect. Moreover, two relatively broad emissions, [g-g] and [g-g]α were noticeably observed which indicated apparent red- and blue-energy shift with increasing net hole concentration |NA - ND|, respectively.