A series of single phase Ba_9−x−ySc_2−zSi₆O₂₄:xCe,yEu,zMn phosphors was synthesized by high-temperature solid-state reactions. The luminescent properties of single-doped, co-doped and tri-doped Ce³⁺/Eu²⁺/Mn²⁺ in the host Ba₉Sc₂Si₆O₂₄ were studied on the basis of the photoluminescence excitation/emission spectra, photoluminescence decay behaviors and time resolved emission spectra. Two types of luminescent centers of Eu(1)/Eu(2,3) as well as Ce(1)/Ce(2,3) occupying different crystallography sites were confirmed, and the sensitizing effects of Ce³⁺ → Eu²⁺, Ce²⁺ → Mn²⁺ and Eu²⁺ → Mn²⁺ were clearly observed. In the tri-doped samples, Eu²⁺ competed with Mn²⁺ for the energy transferred from Ce³⁺ and also transferred its observed energy to Mn²⁺. Furthermore, the tri-doped Ba₉Sc₂Si₆O₂₄ phosphors emitting white light with various correlated color temperatures were obtained by adjusting the relative content of Ce³⁺, Eu²⁺ and Mn²⁺.