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-[(C₂H₅)₄N]MnCl₄ 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.