A series of Ce3+-and Mn2+-(co-) activated SrAl2Si2O8 phosphors have been prepared at 1350 C under a reducing atmosphere and their photoluminescence properties have been studied as a function of the (co-) dopant ions concentrations. We have discovered that energy transfer (ET) not only from Ce3+ to Mn2+ but also from "defects" to Mn2+ by the facts that there is existing significant overlap between the emission spectrum of Ce3+ ("defects") and the excitation spectrum of Mn2+. The source of the "defects" in the host lattice is originated from the different charge substitution between Ce3+ and Sr2+. By adopting the principle of ET, the material SrAl2-Si2O8: Ce, Mn can act as a phosphor for white-light ultraviolet light-emitting diodes (UV-LEDs) by tuning of the dopants contents.