Eu2+/Dy3+-doped Sr2MgSi2O7 powders were synthesized using a solid-state reaction method with flux (NH4Cl). Thebroad photoluminescence (PL) excitation spectra of Sr2MgSi2O7:Eu2+ were assigned to the 4f7-4f65d transition of the Eu2+ ions,showing strong intensities in the range of 375 to 425nm. A single emission band was observed at 470nm, which was the resultof two overlapping subbands at 468 and 507nm owing to Eu(I) and Eu(II) sites. The strongest emission intensity ofSr2MgSi2O7:Eu2+ was obtained at the Eu concentration of 3mol%. This concentration quenching mechanism was attributableto dipole-dipole interaction. The Ba2+ substitution for Sr2+ caused a blue-shift of the emission band; this behavior was discussedby considering the differences in ionic size and covalence between Ba2+ and Sr2+. The effects of the Eu/Dy ratios on thephosphorescence of Sr2MgSi2O7:Eu2+/Dy3+ were investigated by measuring the decay time; the longest afterglow was obtainedfor 0.01Eu2+/0.03Dy3+.