Bi-doped red phosphor series LiEu1-xMo2O8:xBi were prepared by solid-state reactions which present bright red luminescence (615 nm) dominated by a D-5(0)-> F-7(2) transition of Eu3+. With Bi3+ doping, the excitation bands of the phosphors extend to longer wavelength (from 350 to 380 nm), and the excitation efficiency for optimized Bi3+ content is dramatically increased, which favors the phosphors for the white-light ultraviolet light emitting diode applications. The luminescent model for the phosphors studied in this work is proposed. Because the 6p level of Bi3+ is immerged in the conduction band (CB), the excitation 6s -> 6p of Bi3+ is overlapped by the excitation 6s -> CB, which results in extension of the excitation band. The absorbed energy by the excitation 6s -> CB can be effectively transferred to Eu3+, but the 6p -> 6s emission of Bi3+ disappears.