Low energy ion beam sputtering of magnesium exhibits rich and intense optical spectrum containing a number of Mg(T) and Mg(II) lines. It has been found that the emission intensities of Mg(I) and Mg(II) behave differently against the backfilled oxygen pressure. No single explanation can be given for the two different oxygen dependences observed. Considering the similarities with that of secondary ions, it is suggested that the sputtered ions are the precursors for the excited neutral or ionic species formation. It is thought that while the bond-breaking model is appropriate to the excited neutral atom production, the dominant mechanism for excited secondary ion formation is the doubly charged secondary ion production by kinetic processes as proposed by Joyes followed by electron capture processes from the surface.