Scalable Synthesis of Lead‐Free Tetramethylammonium Manganese Halides for Highly Efficient Backlight Displays

Abstract Lead‐free halides have emerged as clean candidates for lighting and display applications because of their superior optoelectronic properties and environmental friendliness. As for the commercialization, the simple synthetic process, scaled production, low‐cost, and excellent performance are the upmost factors. In this work, lead‐free tetramethylammonium manganese halides are quantitatively synthesized using a mechanochemical approach, in which [(CH 3 ) 4 N] 2 MnCl 4 powders show green emission with a photoluminescence quantum yield (PLQY) of 21% and (CH 3 ) 4 NMnCl 3 powders possess red emission with a PLQY of 51%, arising from the intrinsic 4 T 1 ( 4 G) → 6 A 1 ( 6 S) d‐d transition of Mn 2+ . To further boost the green emission efficiency, the composition engineering strategies by Br/Cl substitution and excess organic halide compensation are developed, achieving a high PLQY of 98% for the obtained [(CH 3 ) 4 N] 2 MnBr 4 powders. Furthermore, white light emitting diode (WLED) devices are fabricated by combining green [(CH 3 ) 4 N] 2 MnBr 4 powders with red (CH 3 ) 4 NMnCl 3 powders or single crystals, which exhibit a high luminous efficacy (98.06 or 142.40 lm W −1 ), wide color gamut (over 100 % of NTSC in CIE 1931), and good operating stability (maintained above 80% efficiency after 176 h). This work suggests ball‐milling as a mass synthesis method for metal halides and provides a new Mn 2+ ‐based phosphor for white LEDs in backlight display applications.