Li Substitution Strategy for Enhancing Quantum Efficiency and Improving Thermal Stability of Red-Light Mn⁴⁺-Activated Fluoride for Wide-Gamut Displays

Mn4+-activated red-light fluorides are widely used in high-quality displays, due to the narrow-spectral emission. However, achieving exceptional chromaticity coordinates and appropriate quantum efficiency (QE) at the same time is a great challenge. Herein, a Li substitution strategy is proposed for enhancing QE and improving the thermal stability of red-light Mn4+-activated Cs2NaGaF6 (CNGF). The external quantum efficiency (EQE) of optimal Cs2NaGaF6: Mn4+, Li+ (CNGF: Mn4+, Li+) is improved from 15.79% to 33.61% and thermal stability increases from 68.4% to 85.5% (intensity at 150(degrees)C relative to room temperature). EQE enhancement mechanism on the strategy is explored that Li substitution increases the local structural distortion of Mn4+ for relieving the parity forbidden, and promotes Mn4+ doping in the host lattice, which provides new insights for improving the QE of Mn4+ non-equivalent doped fluorides. Moreover, with exceptional chromaticity coordinates of (0.7029, 0.2970), optimal sample CNGF: 4.8 mol% Mn4+,0.9 mol% Li+ can be used to fabricate white light-emitting diode (w-LED) backlight, which obtains wide color gamut of 110.68% National Television Standards Committee (NTSC) and high luminous efficacy of 110.57 lm W-1, indicating that CNGF: Mn4+, Li+ is a promising candidate for the next generation of wide gamut and efficient displays.