Herein we report an isostructural solid solution of Mg-2(Ti1-x,Sn-x)O-4:0.002Mn (0 <= x <= 1) in which cation substitution leads to the presence of two different Mn luminescence centers. When Mn sources of different valance states (MnCO3/MnO2/Mn3O4) were introduced into Mg2TiO4, the self-redox reaction of MnCO3 occurred in air that can be proved by experimental results, from Mn2+ -> Mn4+ -> Mn3+ and eventually Mn3O4 can be obtained. Low valance state Mn2+/3+ ions in Mn3O4 can be further oxidized to Mn4+ ions by O-2 in Mg2TiO4:Mn.Mn4+ red emission can be observed along with oxygen defects-induced blue emission in Mg-2(Ti1-xSnx)O-4:Mn (0 <= x < 1). Eventually, the spectral emission of Mn4+ was converted to that of Mn2+, green emission, in Mg2SnO4:Mn though electrons transfer from oxygen vacancies (V-0(center dot)) to Mn3+. This is the first time that compositional-tunability that induces Mn ions of different valance states luminescent behaviors and further interprets its spectral transition mechanism.