A new orange–red phosphor Sr 3 P 4 O 13 : Eu was synthesized by a high temperature solid-state reaction. X-ray powder diffraction (XRD) analysis confirms the formation of Sr 3 P 4 O 13 in a triclinic system with space group P1¯. The photoluminescence spectra indicate that Sr 3 P 4 O 13 : Eu can be excited effectively by near ultraviolet (NUV) light and exhibit bright orange–red emission with excellent color stability. Interestingly, the emission bands of Eu 2+ and Eu 3+ were both observed in the photoluminescence spectra of air-sintered Sr 3 P 4 O 13 : Eu phosphor due to the self-reduction effect. This kind of abnormal reduction was explained by a charge compensation model.