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The development of metal‐halide perovskite nanocrystals (NCs) that yield bright and stable emission is of great importance. Previous reported perovskite NCs are mostly based on APbX3‐type family fabricated via ligand‐ or surfactant‐assisted chemical approaches. However, realizing bright and stable emission remains a challenge because of desorption of ligands/surfactants during long‐term operation. Herein, Ruddlesden–Popper (RP)‐type (A)2(MA)n‐1PbnBr3n+1 NCs with size less than Bohr radius stabilized in mesoporous silica scaffold, which are prepared in situ via physical approach at low temperature are introduced. The RP NCs in mesoporous silica exhibit the formation of spatially and electronically separated quantum wells, efficient energy funneling between different n phases for bright emission (photoluminescence quantum yields of ≈99%), high irradiation stability (T70 = 110 days), and long‐term stability (T90 = 110 days). These RP NCs have broad potential for bright light‐emitting diodes, high‐resolution PL imaging, and waterproof inks. Importantly, for the first time, stretchable perovskite X‐ray scintillator is demonstrated with excellent X‐ray imaging with resolution greater than 14 line pairs mm−1. These findings offer a paradigm to motivate future research toward stable and efficient perovskite optoelectronics. [ABSTRACT FROM AUTHOR]

The development of metal‐halide perovskite nanocrystals (NCs) that yield bright and stable emission is of great importance. Previous reported perovskite NCs are mostly based on APbX3‐type family fabricated via ligand‐ or surfactant‐assisted chemical approaches. However, realizing bright and stable emission remains a challenge because of desorption of ligands/surfactants during long‐term operation. Herein, Ruddlesden–Popper (RP)‐type (A)2(MA)n‐1PbnBr3n+1 NCs with size less than Bohr radius stabilized in mesoporous silica scaffold, which are prepared in situ via physical approach at low temperature are introduced. The RP NCs in mesoporous silica exhibit the formation of spatially and electronically separated quantum wells, efficient energy funneling between different n phases for bright emission (photoluminescence quantum yields of ≈99%), high irradiation stability (T70 = 110 days), and long‐term stability (T90 = 110 days). These RP NCs have broad potential for bright light‐emitting diodes, high‐resolution PL imaging, and waterproof inks. Importantly, for the first time, stretchable perovskite X‐ray scintillator is demonstrated with excellent X‐ray imaging with resolution greater than 14 line pairs mm−1. These findings offer a paradigm to motivate future research toward stable and efficient perovskite optoelectronics. [ABSTRACT FROM AUTHOR]

Environmental friendly metal halides have become emerging candidates as energy downconverting emitters for lighting and X‐ray imaging applications. Herein, luminescent single crystals of tetramethylammonium manganese chloride (C4H12NMnCl3) and tetraethylammonium bromide ((C8H20N)2MnBr4) are synthesized via a facile room‐temperature evaporation method. C4H12NMnCl3 and (C8H20N)2MnBr4 with octahedrally and tetrahedrally coordinated Mn2+ have correspondingly exhibited red and green emission peaking at 635 and 515 nm both originating from 4T1–6A1 transition of Mn2+ with high photoluminescence quantum yield (PLQY) of 91.8% and 85.1% benefiting from their specific crystal structures. Thanks to their strong photoexcitation under blue light, high PLQY, tunable emission spectra, good environmental stability, the white light‐emitting diode based on blending of C4H12NMnCl3 and (C8H20N)2MnBr4 delivers an outstanding luminous efficacy of 96 lm W−1, approaching commercial level, and shows no obvious photoluminescence intensity degradation after 3000 h under operation. In addition, manganese halides also demonstrate interesting characteristics under X‐ray excitation, C4H12NMnCl3 and (C8H20N)2MnBr4 exhibit steady‐state X‐ray light yields of 50 500 and 24 400 photons MeV−1, low detectable limits of 36.9 and 24.2 nGyair s−1, good radiation hardness, and X‐ray imaging demonstration with high‐resolution of 5 lp mm−1. This work presents a new avenue for luminescent Mn‐based metal halides toward multifunctional light‐emitting applications. [ABSTRACT FROM AUTHOR]