Crystal-site engineering approach for preparation of Mg B2O4:Mn2+, Mn4+ (B = Al, Ga) phosphors: Control of green/red luminescence properties

•The luminescence color of Mg B2O4:Mn (B=Al, Ga) was controlled by crystal-site engineering approach.•The samples prepared through adjusting the quantity of MgO in raw materials.•The samples with deficient-MgO and excess-MgO showed only green and red emission.•The stoichiometric samples (Mg/B=1:2) indicated both green and red luminescence.•We proposed the mechanism of green/red luminescence in Mn-doped Mg B2O4 (B=Al, Ga) phosphors.