ZnS:Cu:Cl and ZnS:Cu:Al phosphors are fabricated by a flux fusion method to be used in cathode ray tube (CRT) monitors for green emission. The emission spectra of the phosphors depend on the Cu concentration. A series of luminescence measurements have been conducted, and several models are applied to explain the luminescent phenomenon of these phosphors. It is revealed that ZnS:Cu:Cl and the ZnS:Cu:Al phosphors exhibit green emission yet their luminescence mechanisms are different. The emission spectrum from the as-fabricated green phosphors is not a typical Gaussian distribution. The combination of blue and green band luminescence is attributed to the green-luminescence quenching derived from the interstitial Cu+ ions.