Design Principles for Enhancing Photoluminescence Quantum Yield in Hybrid Manganese Bromides

Abstract

Hybrid manganese halides have attracted widespread attention on account of their highly emissive optical properties. To understand the underlying structural factors that dictate the photoluminescence quantum yield (PLQY) of these materials, we report five new hybrid manganese bromides with the general formula AmMnBr4 [m = 1 or 2, A = dimethylammonium (DMA), 3methylpiperidinium (3-MP), 3-aminometylpiperidinium (3AMP), heptamethylenimine (HEP) and trimethylphenylammonium (TMPEA)]. By studying the crystal structures and optical properties of these materials and combining our results with the findings from previously reported analogs, we have found a direct correlation between Mn … Mn distance and the PLQY, where high PLQYs are associated with long Mn … Mn distances. This effect can be viewed as a manifestation of the concentration-quenching effect, except these are in stoichiometric compounds with precise interatomic distances, rather than random alloys. To gain better separation of the Mn centers and prevent energy transfer, a bulky singly-protonated cation that avoids H-bonding is ideal. We have demonstrated this principle in one of our newly reported material, (TMPEA)2MnBr4, where a PLQYs of 70.8 % for a powder sample and 98 % for a large single crystal sample is achieved. Our study reveals a generalized method for improving PLQYs in hybrid manganese bromides and is readily extended to designing all varieties of highly emissive hybrid materials.

Mn2+‐Doped Metal Halide Perovskites: Structure, Photoluminescence, and Application

“…Importantly, the PLQY is closely relative to nearest Mn─Mn distance, where the sufficiently long Mn─Mn distance is the prerequisite for realizing high PLQY in these 0D Mn 2+ ‐based metal halides. [ 26,207 ] This inspires us to adopt similar design principles not only to optimize PLQY and other unique performances, such as optical, electrical, and magnetic properties. To fully understand the effect of Mn─Mn coupling interactions on the properties of Mn 2+ ‐related emission in metal halide perovskites, some advanced characterization methods should be used, which can provide some detailed information on the local structures of Mn 2+ . Artificial intelligence (AI) learning can better help us to analyze the relationship between structure and properties. For example, we can construct the relationship between distance (Me─Me/X, Me: central metal ion; X: halogen) and PLQY or emission wavelength for the discovery of compounds in the current database that meet the predicted results.…”

“…Importantly, the PLQY is closely relative to nearest Mn─Mn distance, where the sufficiently long Mn─Mn distance is the prerequisite for realizing high PLQY in these 0D Mn 2+ ‐based metal halides. [ 26,207 ] This inspires us to adopt similar design principles not only to optimize PLQY and other unique performances, such as optical, electrical, and magnetic properties.…”

“…also propose the similar conclusion that a direct correlation exists between Mn─Mn distances and the PLQY, where the longer the Mn─Mn distances, the higher the PLQY. [ 207 ] In addition, they reveal the significance of organic cation in hybrid Mn 2+ ‐based halides for realizing the high PLQY (Figure 15d). The bulky singly protonated cation that avoids H‐bonding is essential, it can effectively separate Mn 2+ centers and prevent energy transfer.…”

“…d) Schematic diagrams of [MnBr 4 ] 2− tetrahedral structure in different environments. [ 207 ] The insets are crystal photograph of Mn 2+ ‐based halide at visible and UV light. a) Reproduced with permission.…”

“…It is worth noting that this work has practical guiding significance in the development of high‐efficiency Mn 2+ ‐based emitters from the perspective of Mn─Mn distance, and similar views have been further proved in the same period. [ 207 ] Besides, Mn 2+ ‐doped halides can also be used for electroluminescence (EL) devices. Congreve's group found that the doping engineering of Mn 2+ ions can significantly improve the PQLY and chemical stability of perovskites.…”