Two series of single-composition (Ca,Mg,Sr) 9 Y(PO 4 ) 7 :Eu 2+ and (Ca 0.5 Sr 0.5 ) 9 Y(PO 4 ) 7 :Eu 2+ ,Mn 2+ phosphors were synthesized via high-temperature solid-state reactions. Their emission colors could be tuned from blue to green and eventually to red through tuning the crystal field splitting and energy transfer. On examining the Mn 2+ concentration-dependent photoluminescence properties, we found that co-doping with Mn 2+ would lead to a change in Eu 2+ /Eu 3+ ratio. Moreover, an energy transfer from Eu 2+ to Mn 2+ occurs because of the spectral overlap between the emission band of Eu 2+ and the excitation band of Mn 2+ . The resonance-type energy transfer via a dipole-quadrupole interaction mechanism was supported by decay lifetime data and the critical distance of energy transfer was calculated to be 11.09 Å. A trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca 0.5 Sr 0.5 ) 9 Y(PO 4 ) 7 :0.007Eu 2+ ,0.02Mn 2+ and blue-emitting (Ca 0.5 Mg 0.5 ) 9 Y(PO 4 ) 7 :0.007Eu 2+ phosphors into a single package. Such a composite device emitted white light with a correlated color temperature of 6303 K, a color rendering index of 87.4, and color coordinates (0.314, 0.348) close to those of ideal white light. The results suggest that a phosphor blend of (Ca 0.5 Sr 0.5 ) 9 Y(PO 4 ) 7 :0.007Eu 2+ ,0.02Mn 2+ and (Ca 0.5 Mg 0.5 ) 9 Y(PO 4 ) 7 :0.007Eu 2+ is potentially useful for white n-UV light-emitting diodes (LEDs).