Be2+‐Induced Red Emission Enhancement in CaAl12O19:Mn4+ for Wide Color Gamut Display: Suppressing Self‐Reduction of Mn4+ to Mn2+

Abstract Mn 4+ ‐activated CaAl 12 O 19 (CAO: Mn 4+ ) is recognized as a promising candidate for red phosphor used in wide color gamut displays. However, the spontaneous self‐reduction of Mn 4+ to Mn 2+ occurs for charge compensation through Mn 2+ ‐Mn 4+ substitution for Al 3+ ‐Al 3+ , lowering the quantum efficiency of Mn 4+ . To suppress the self‐reduction, some divalent metal ions, including Ba 2+ , Sr 2+ , Cd 2+ , Zn 2+ , and Mg 2+ , are added for charge compensation instead of Mn 2+ , but only small luminescence enhancement is observed. In this paper, remarkable luminescence enhancement in CAO: Mn 4+ via co‐doping Be 2+ is reported. The photoluminescence properties are studied as a function of Be 2+ doping concentration, and the optimal Be 2+ concentration of 0.01 is found. The internal quantum efficiency of 74.9% and external quantum efficiency of 56.3% are achieved under UV excitation, higher than those via co‐doping other divalent metal ions. This study indicates that the addition of Be 2+ dominates the charge compensation because Be 2+ is closer to Al 3+ in size than Mn 2+ and other divalent metal ions. The backlight light‐emitting diodes using CAO: Mn 4+ , Be 2+ are fabricated, exhibiting a 110.1% Nation Television Standards Committee (NTSC) color gamut, wider than both the current commercial backlight using K 2 SiF 6 : Mn 4+ (KSF) red phosphor and the conventional one using YAG yellow phosphor.