Localized Charge Accumulation Driven by Li+ Incorporation for Efficient LED Phosphors with Tunable Photoluminescence

Mn4+ ion-doped red-emitting oxides are promising candidates for light-emitting-diode phosphors, but the formation and stabilization of Mn4+ in the oxide matrix remain a challenge due to the spontaneous reduction of Mn4+ to Mn2+. In this work, we demonstrate that the incorporation of Li+ can regulate the valence of Mn ions doped in spinel-phase ZnAl2O4 and enable tuning of the luminescence of Mn2+ and Mn4+ dopants. Both experimental and calculation results show that the incorporation of Li+ ions can lead to localized charge accumulation around themselves, thereby consuming the excess charges and suppressing the self-reduction of Mn4+. This finding allows for the realization of pure red emission of Mn4+ in ZnAl2O4 for the first time and the fabrication of a corresponding warm white-light-emitting-diode prototype. The Li+-dependent dual emission of Mn2+ (green) and Mn4+ (red) co-doped in ZnAl2O4 can be conveniently utilized to design a ratiometric optical thermometer with excellent visual responses. This work not only offers new atomistic insights into regulating the valence state of Mn ions but also provides an effective method for improving the performance of Mn4+-activated light-emitting-diode phosphors and devising a good phosphorescent probe for fluorescence-intensity-ratio temperature sensing.