A series of Eu2+ and Mn2+ coactivated Ca3Al2(SiO4)3−δCl4δ phosphors have been synthesized by solid state reactions and their luminescence properties have been investigated by means of powder diffuse reflection, photoluminescence excitation and emission spectra, and lifetimes. The phosphor Ca3Al2(SiO4)3−δCl4δ:Eu2+, Mn2+ exhibits two dominating bands situated at 460 and 550 nm, originate from the allowed 5d → 4f transition of the Eu2+ ion and the 4T1g(4G) → 6A1g(6S) transition of the Mn2+ ion, respectively. We have discovered that energy transfers from Eu2+ to Mn2+ by directly observing significant overlap of the excitation spectrum of Mn2+ and the emission spectrum of Eu2+ as well as the decline of lifetimes of Eu2+. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content Ca3Al2(SiO4)3−δCl4δ:Eu2+, Mn2+ phosphors exhibit potential to act as a phosphor for near ultraviolet light-emitting diodes.