Green and red photoluminescence (PL) is obtained from manganese activated phosphor CaAl₁₂O₁₉ (CAO) synthesized using a solid-state reaction method. The red PL is attributed to Mn⁴⁺ at an octahedral Al³⁺ site and the green PL is from Mn²⁺ at a tetrahedral Al³⁺ site. Thermal reduction of Mn⁴⁺ to Mn²⁺ in CAO lattice does not complete, even in a reducing atmosphere, but can be fully realized through co-doping of trivalent ions such as Bi³⁺ and La³⁺ with ion radii similar to that of Ca²⁺. The intensity of the Mn²⁺ green luminescence strongly depends on the co-doping concentration of the trivalent ions.