The effects of local excitation density and of applied electric field on the luminescence spectra of CdS and CuCl induced by bombardments with MeV H+or He+have been studied. It is found that the intensity of theMline (4870 Å) relative to that of thePline (4906 Å) in CdS increases as the local excitation density increases and the intensity of theMline is reduced by applied electric field. The ratio of the intensity of theMT(3911 Å) andML(3918 Å) lines to that of theXline (3926 Å) in CuCl is found to be almost insensitive to the local excitation density and the intensities of each line are insensitive to applied electric field. TheXline is also found to be less sensitive to the radiation induced defects than theMTandMLlines. Theoretical calculation of the thermalization of the electrons and holes in an ion track is also made, showing that the density of electrons and holes in ion tracks is sufficiently high for the electron-hole plasma to be created. It is suggested that theMline in CdS and theXline in CuCl is due to the electron-hole plasma. With this assignment the dependence of the intensity of each luminescence line on the excitation density and on the applied electric field and their line shapes are explained.