Synthesis, structure and tunable red emissions of Ca(Al/Si)2N2(N1−xOx):Eu2+prepared by alloy-nitridation method

► Eu-doped Ca(Al/Si)2N2(N1−xOx) were synthesized by alloy-nitridation method. ► Two types of Eu2+-coordination modes are formed due to preferential occupancy of oxygen. ► Two types of Eu2+-coordination modes account for luminescence properties.