Tb 3+ activated Sr 4 Al 14 O 25 phosphors were synthesized by the high temperature solid-state reaction. For the sample, the color of the photoluminescence (PL) was green, but that of the afterglow was blue. The spectral results indicated that the photoluminescence was mainly due to the transitions from 5 D 4 to the ground energy levels of Tb 3+ and obeyed the cross-relaxation mechanism; however, the afterglow was derived from the transitions from 5 D 3 and independent with the concentration of Tb 3+ . This difference was attributed to the reason that the energy transfer process of cross-relaxation was halted by the traps during the period of afterglow.