The synthesis, luminescence, and potential applications in white light diodes of Mn4+/Si4+ codoped Y3Al5O12 phosphors are presented. The Mn4+ doped Y3Al5O12 phosphor shows the deep red emission with a strongest emission peak at about 646 nm. By codoping Si4+ in Y3Al5O12:Mn4+, the intensity and peak wavelength of Mn4+ emission are tuned. The appropriately codoped Si4+ can enhance the Mn4+ emission intensity due to the formation of Mn4+-Si4+-O2- pairs. The formed Mn4+-Si4+-O2- pairs interrupts the energy migration from Mn4+ to O2- quenching centers. The codoped Si4+ also induces the blue shift of Mn4+ emission since the substitution of Al23+ by smaller Si4+ leads to a longer Mn-O bond length.