Mixed-Ligand Engineering to Enhance Luminescence of Mn2+-Based Metal Halides for Wide Color Gamut Display

Lead-free Mn2+-based metal halide materials are now being considered as clean candidates for backlight displays and lights due to the d–d transition, diverse components, and environmental friendliness. Therefore, efficient and stable Mn2+-based metal halide phosphors are in great demand for practical applications. In this work, adopting the mixed-ligand strategy, a series of [(CH3)4N]2−x[(C2H5)4N]xMnCl4 phosphors were synthesized by mechanochemical process. With the increase molar ratio of (CH3)4N/(C2H5)4N, the phase of phosphors is transformed from orthorhombic to tetragonal. Compared to [(CH3)4N]2MnCl4 and [(C2H5)4N]2MnCl4 phosphors, the mixed-ligand strategy significantly boosts the green emission intensity of Mn2+-based metal halide phosphors. The obtained [(CH3)4N][(C2H5)4N]MnCl4 phosphors exhibit a high photoluminescence quantum yield (PLQY) of 83.78% under 450 nm excitation, which is attributed to the modulation of the adjacent [MnCl4]2- distance by using the different chain length of organic cations, effectively suppressing non-radiative recombination. Additionally, the [(CH3)4N][(C2H5)4N]MnCl4 phosphors exhibit a green emission at 516 nm, narrow full width at half-maximum (FWHM) of 45.53 nm, and good thermal stability. The constructed white light-emitting diode (WLED) device exhibits a wide color gamut of 108.3% National Television System Committee, demonstrating the suitability of the [(CH3)4N][(C2H5)4N]MnCl4 phosphors as a green emitter for WLED displays and lightings. This work provides a new way to modulate the PL performance of manganese-based metal halides for application in the optoelectronic field.