Unraveling the Near-Unity Narrow-Band Green Emission in Zero-Dimensional Mn-Based Metal Halides: A Case Study of (CHN)ZnMnBr Solid Solutions.

Zero-dimensional (0D) Mn-based metal halides are potential candidates as narrow-band green emitters, and thus it is critical to provide a structural understanding of the photophysical process. Herein, we propose that a sufficiently long Mn-Mn distance in 0D metal halides enables all Mn centers to emit spontaneously, thereby leading to near-unity photoluminescence quantum yield. Taking lead-free (CHN)ZnMnBr ( = 0-1) solid solution as an example, the Zn/Mn alloying inhibits the concentration quenching that is caused by the energy transfer of Mn. (CHN)MnBr exhibits highly thermal stable luminescence even up to 150 °C with a narrow-band green emission at 518 nm and a full width at half maximum of 46 nm. The fabricated white light-emitting diode device shows a high luminous efficacy of 120 lm/W and a wide color gamut of 104% National Television System Committee standard, suggesting its potential for liquid crystal displays backlighting. These results provide a guidance for designing new narrow-band green emitters in Mn-based metal halides.