In order to uncover the real origin of red luminescence from Sr_3Al_2O_6:Eu and the physical mechanisms that were involved in the dynamical process of luminescence, variant amount of Eu and Dy activated Sr_3Al_2O_6 phosphors were synthesized with the solid-state reaction and the combustion-assisted solid-state reaction, respectively, using the fine graphite powder or the mixed H_~(2+)N_2gases as a reducing agent. The phase was examined with XRD analysis and the photoluminescence properties were characterized by a fluorescence spectrometer. Although the phosphors possessed the same Sr_3Al_2O_6 phase, different emission colors(red or green) were obtained, relying on synthesis conditions. The simultaneous existence of Eu~(2+) and Eu~(3+) was not only observed in the emission and excitation spectra, but also identified with the near edge X-ray absorption fine structure spectroscopy(NEXAFS).The mixed valence(higher than +2 and less than +3) of Eu may be related with the six different sites of Sr, whose effective valence ranged from +1.5058 to +2.2698, in the crystal lattice of Sr_3Al_2O_6 that could accommodate Eu. Moreover, the reduction of Eu~(3+) to forming Eu~(2+) depended on the amount of Eu~(3+) or Dy~(3+) doped, due to the different energy barrier in each site of Sr that Eu had to overcome. The residual Eu~(3+), similar to the doped Dy~(3+), played an important role in supplying the hole for Eu~(~(2+)) to form a bound trap(Eu~(2+))* after excitation. During electron returning to the 4f~7 ground state of Eu~(2+), the red luminescence was radiated. Therefore, the synergetic effects of Eu~(2+) and Eu~(3+)(Dy~(3+)) produce red luminescence. In order to uncover the real origin of red luminescence from Sr_3Al_2O_6: Eu and the physical mechanisms that were involved in the dynamical process of luminescence, variant amount of Eu and Dy activated Sr_3Al_2O_6 phosphors were synthesized with the solid-state reaction and the combustion-assisted solid-state reaction, respectively, using the fine graphite powder or the mixed H_ ~ (2+) N_2gases as a reducing agent. The phase was examined with XRD analysis and the photoluminescence properties were characterized by a fluorescence spectrometer. Although the phosphors possessed the The simultaneous existence of Eu ~ (2+) and Eu ~ (3+) was not only observed in the emission and excitation spectra, but also identified with the near edge X-ray absorption fine structure spectroscopy (NEXAFS). The mixed valence (higher than +2 and less than +3) of Eu may be related with the six different sites of Sr, whose effective valence ranged from +1.5058 to +2.2698, in the crystal lattice of Sr_3Al_2O_6 that could accommodate Eu. Moreover, the reduction of Eu ~ (3 +) to forming Eu ~ (2+) depended on the amount of Eu (3+) or Dy ~ (3+) doped, due to the different energy barrier in each site of Sr that Eu had to overcome. The residual Eu ~ (3+), similar to the doped Dy ~ (3+) , played an important role in providing the hole for Eu ~ (2+) to form a bound trap (Eu ~ (2 +)) * after excitation. During electron returning to the ground state of Eu ~ ( 2+), the red luminescence was radiated. Thus, the synergetic effects of Eu 2+ and Eu 3+ Dy 3+ produce red luminescence.