A series of single-component red/white-emitting CaScAlSiO6:Ce3+,Tb3+,Mn2+ phosphors have been synthesized by a solid-state reaction. It is observed that CaScAlSiO6:Ce3+,Tb3+ phosphors exhibit two dominating bands situated at 380 and 542 nm, originating from the allowed 5d -> 4f transition of the Ce3+ ion and the D-5(4) -> F-7(J) = (J = 6, 5, 4, 3) transition of the Tb3+ ion, respectively. As for CaScAlSiO6:Ce3+,Mn2+, our results indicate that Mn2+ may occupy not only a Ca2+ site to generate an orange emission [Mn2+(I)] at 590 nm but also a Sc3+ site to generate a red emission [Mn2+(II)] at 670 nm. Both energy transfers from Ce3+ to Tb3+ and from Ce3+ to Mn2+ in the CaScAlSiO6 host are investigated and have been demonstrated to be of the resonant type via a dipole dipole mechanism. By proper tuning of the relative composition of Tb3+/Mn2+, white light can also be achieved upon excitation of UV light, indicating that the developed phosphor may potentially be used as a single-component red/white-emitting phosphor for UV-light-emitting diodes.