Fig. 4: Thermal quenching in Mn⁴⁺-doped fluorides.

a, b Configuration coordinate diagrams showing luminescence quenching due to a thermally activated crossover via the F⁻ → Mn⁴⁺ charge-transfer (CT) state and b thermally activated crossover via the Mn^{4+ 4}T₂ excited state. c Quenching temperature T_½ of Mn⁴⁺-doped fluoride phosphors as a function of the ⁴A₂ → ⁴T₂ transition energy. The red dashed line is a linear fit to the data points. d Quenching temperature T_½ of Mn⁴⁺-doped fluorides (blue dots) and Mn⁴⁺-doped oxides (red dots) as a function of the ⁴A₂ → ⁴T₂ transition energy