Rare earth ions (Ce3+, Eu2+) activated Ca 3Mg Si2O8 (CMSO) phosphors have been synthesized using solid-state reaction method in 95%N2 + 5%H 2 reduction atmosphere at elevated temperatures by varying Eu 2+ concentration from 0.0075 to 0.0300 at the fixed Ce0.03 concentration to study their photoluminescence (PL) properties. An energy transfer occurs from Ce3+ to Eu2+ through a significant overlap of Eu2+ excitation spectrum with Ce3+ emission spectrum in CMSO, together with the systematic relative decrease and increase in emission bands of Ce3+ and Eu2+, respectively, have been observed. To support the phenomenon, diffuse reflectance spectra show various absorption levels corresponding to Ce3+, Eu2+, and/or mixture of both rare earth ions. An optimum emission was realized at 0.0150 of Eu2+ via. energy transfer from Ce3+ ion. By utilizing the principle of energy transfer, the critical distance (Rc) between activator ions was found to be 18.64 Å. The CIE chromaticity coordinates measured on the Ca3MgSi2O8:Ce3+, Eu2+ phosphors excited under ultraviolet (365 nm) source shows the values lie in cool white light region could be applied to solid state lighting. © Springer-Verlag 2010.