Single-doped(Ce~(3+),Tb~(3+)), co-doped(Ce~(3+)-Tb~(3+), Ce~(3+)-Yb~(3+), Tb~(3+)-Yb~(3+)) and tri-doped(Ce~(3+)-Tb~(3+)-Yb~(3+)) Y_3Al_5O_(12) phosphors were synthesized by a solid-state reaction method. The XRD, excitation and emission spectra and the fluorescence lifetime of the samples were measured. The energy transfer mechanism was also investigated. The results showed that the energy transfer efficiency from Tb~(3+) to Ce~(3+) was 51% and the energy transfer efficiency from Ce~(3+) to Yb~(3+) was 63.1%. Concomitantly, both were more efficient than that from Ce~(3+) to Tb~(3+)(7%) and from Tb~(3+) to Yb~(3+)(10.2%). Also, the Yb~(3+) ions received energy mainly from Ce~(3+) ions in Ce~(3+)-Tb~(3+)-Yb~(3+) tri-doped Y_3Al_5O_(12) phosphors. Among these materials, Ce~(3+)-Yb~(3+) co-doped YAG phosphors are a better choice than others as a down-conversion material due to their higher energy transfer efficiency. Single-doped (Ce ~ (3 +), Tb ~ (3+)), co-doped Ce ~ (3 +) - Tb ~ Tb 3+ - Yb 3+ and tri - doped Ce 3+ - Tb 3+ - Yb 3+ Y 3 Al 5 O 12 phosphors were synthesized by a The energy transfer mechanism was also investigated. The energy transfer mechanism was also investigated. The results showed that the energy transfer efficiency from Tb ~ (3+) to Ce ~ ( 3+) was 51% and the energy transfer efficiency from Ce ~ (3+) to Yb ~ (3+) was 63.1%. Concomitantly, both were more efficient than that from Ce ~ (3+) to Tb ~ (3+) (3+) to Yb ~ (3 +) (10.2%). Also, the Yb ~ (3 +) ions received energy mainly from Ce ~ (3+) ions in Ce ~ ( (3+) - Yb ~ (3+) tri-doped Y_3Al_5O_ (12) phosphors. Among these materials, Ce ~ (3 +) - Yb 3+ co- doped YAG phosphors are a better choice than others as a down-conversion material due to their higher energy transfer efficiency.