In this article, we report the preparation and luminescence properties of a series of novel rare-earth doped KBaY(MoO4)3 phosphors. The XRD patterns for the as-prepared samples have been assigned to the pure KBaY(MoO4)3 phase. The Tb3+, Eu3+ and Sm3+ singly-doped phosphors all show good luminescence properties with their characteristic excitations and emissions. We have optimized the rare-earth ion doping concentrations, yielding the compositions KBaY0.60(MoO4):0.40Tb3+, KBaY0.50(MoO4):0.50Eu3+ and KBaY0.96(MoO4):0.04Sm3+ with corresponding quantum yields of 15.80% (λex = 376 nm), 40.67% (λex = 392 nm) and 16.79% (λex = 402 nm), respectively. In addition, we have chosen co-doping of Tb3+/Eu3+ and Tb3+/Sm3+ into the host to realize tunable emission colors. We have observed energy transfer from Tb3+ to Eu3+ and from Tb3+ to Sm3+ ions in the as-prepared samples, which resulted in tunable emission colors from green to red and to orange-red under UV excitation, respectively. Moreover, investigation of the excitation and emission spectra, and decay lifetimes with increasing doping concentrations confirmed efficient energy transfer from Tb3+ to Eu3+ and from Tb3+ to Sm3+ ions in the co-doped samples. We also analyzed the energy transfer mechanisms between Tb3+ and Eu3+ and between Tb3+ and Sm3+ and both were determined to be dipole-dipole interactions. These results show that the as-prepared materials could serve as candidate phosphors for use in UV-pumped w-LEDs.