Eu 3+ and Sm 3+ activated double molybdates, KY 1−x Ln x (MoO 4 ) 2 (Ln=Sm 3+ , Eu 3+ ), were synthesized by a convenient solid-state method. The photoluminescence properties, energy transfer and concentration quenching were investigated in the excitation and emission spectra. The results exhibit that with Sm 3+ and Eu 3+ ions co-doped into the host, the excitations around 394nm and 465nm become broader and their intensities are prominently enhanced compared to that of the single Eu 3+ doped sample. The effective energy transfer from Sm 3+ to Eu 3+ is found to exist for Sm 3+ and Eu 3+ co-doped KY(MoO 4 ) 2 phosphors. Besides, with increasing Eu 3+ doping concentration, the chromaticity coordinates of KY 1−x Ln x (MoO 4 ) 2 (Ln=Sm 3+ , Eu 3+ ) approach to the NTSC standard values in a systematic way. The KY(MoO 4 ) 2 :Sm 3+ , Eu 3+ phosphors may be potentially used as red phosphors for white light-emitting diodes.