The structure transition and luminescence performance of a high moisture resistant KNaNbOF5:Mn4+ red phosphor

The relationship between the luminescence performance and structure of an Mn⁴⁺-doped oxyfluoride phosphor is a key factor in developing an incredible phosphor. Herein, a pair of novel KNaNbOF₅:Mn⁴⁺ phosphors (α- and β-type) was successfully synthesized by controlling HF usage. The structures, morphologies and luminescence properties, including thermal quenching and moisture resistance, of the phosphors were systematically studied. The optimal Mn⁴⁺ doping concentrations of the two phosphors were 1% mol. The α-type phosphor shows stronger luminous intensity and better thermal quenching resistance. Its thermal quenching temperature (T_1/2) is about 350 K and quantum efficiency is 60.74%. Correspondingly, the β-type phosphor exhibits a strong zero phonon line emission located at 626 nm and an obvious red shift. Fluorescence lifetimes were fitted to 2.18 ms and 1.07 ms for the α- and β-type phosphors, respectively. Both of the phosphors exhibit excellent moisture resistances with 90.6% and 88.1% initial intensities after 24 h water immersion. The above results demonstrate the promising application of the as-prepared KNaNbOF₅:Mn⁴⁺ phosphors in the field of warm-WLEDs.