Reduction of Mn4+ to Mn2+ in CaAl12O19 by co-doping charge compensators to obtain tunable photoluminescence

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.