Non-equivalent Mn4+ doping into A2NaScF6 (A = K, Rb, Cs) hosts toward short fluorescence lifetime for backlight display application

Mn4+-doped fluoride red-emitting phosphors have been developed for backlighting white light-emitting diodes (WLEDs). However, the long fluorescence lifetime (τ > 5 ms) leads to the image-retention phenomenon for the human eye when Mn4+ is doped into equivalent X sites in A2XF6 (A = Na, K, Rb, Cs; X = Si, Ge, Ti, Zr). Herein, we report on novel red-emitting A2NaScF6:Mn4+ (A = K, Rb, Cs) (ANSF) phosphors with short fluorescence lifetimes (τ < 4 ms) and characteristic zero phonon line (ZPL) emission, which can be realized via non-equivalent doping of Mn4+ into Sc3+ sites. Density functional theory (DFT) calculations verified the formation of a slightly distorted environment of Mn4+ and an Na+ vacancy to balance the charge with Mn4+ non-equivalent doping. The WLED backlight using ANSF as a red-light component can reach a wide color gamut above 105% of the National Television Standards Committee (NTSC) standard, and the image-retention on the backlighted screen can be effectively avoided compared to the backlight obtained using commercial K2SiF6:Mn4+. Such a Mn4+ non-equivalent doping strategy opens a new perspective for the modification of local symmetry and enhancement of the luminescence properties of Mn4+-doped red-emitting fluoride phosphors.