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2D hybrid perovskites are attractive for optoelectronic devices. In thin films, the color of optical emission and the texture of crystalline domains are often difficult to control. Here, a method for extinguishing or enhancing different emission features is demonstrated for the family of 2D Ruddlesden–Popper perovskites (EA1−xFAx)4Pb3Br10 (EA = ethylammonium, FA = formamidinium). When grown from aqueous hydrobromic acid, crystals of (EA1−xFAx)4Pb3Br10 retain all the emission features of their parent compound, (EA)4Pb3Br10. Surprisingly, when grown from dimethylformamide (DMF), an emission feature, likely self‐trapped exciton (STE), near 2.7 eV is missing. Extinction of this feature is correlated with DMF being incorporated between the 2D Pb‐Br sheets, forming (EA1−xFAx)4Pb3Br10∙(DMF)y. Without FA, films grown from DMF form (EA)4Pb3Br10, retain little solvent, and have strong emission near 2.7 eV. Slowing the kinetics of film growth strengthens a different emission feature, likely a different type of STE, which is much broader and present in all compositions. Films of (EA1−xFAx)4Pb3Br10∙(DMF)y have large, micron‐sized domains and homogeneous orientation of the semiconducting sheets, resulting in low electronic disorder near the absorption edge. The ability to selectively strengthen or extinguish different emission features in films of (EA1−xFAx)4Pb3Br10∙(DMF)y reveals a pathway to tune the emission color in these compounds. [ABSTRACT FROM AUTHOR]

The aerobic photochemical oxidation of benzylamine was carried out on the ternary oxides CuWO4 and BiVO4 as a test proton-coupled-electron-transfer reaction in acetonitrile. Both oxides give the coupled imine product, N-benzylidenebenzylamine, in near quantitative (98–99%) yield, with rate constants of 0.34 h−1 g−1 and 0.70 h−1 g−1 for CuWO4 and BiVO4, respectively. [ABSTRACT FROM AUTHOR]

Metal sulfide ion exchange materials (MSIEs) are of interest for nuclear waste remediation applications. We report the high stability of two structurally related metal sulfide ion exchange materials, Na 2 x Mg 2 y - x Sn 4- y S 8 (Mg-NMS) and Na 2 SnS 3 (Na-NMS), in strongly acid media, in addition to the preparation of Na 2 x Ni 2 y - x Sn 4- y S 8 (Ni-NMS). Their formation progress during synthesis is studied with in-situ methods, with the target phases appearing in <15 min, reaction completion in <12 h, and high yields (75-80%). Upon contact with nitric or hydrochloric acid, these materials topotactically exchange Na + for H + , proceeding in a stepwise protonation pathway for Na 5.33 Sn 2.67 S 8 . Na-NMS is stable in 2 M HNO 3 and Mg-NMS is stable in 4 M HNO 3 for up to 4 h, while both NMS materials are stable in 6 M HCl for up to 4 days. However, the treatment of Mg-NMS and Na-NMS with 2-6 M H 2 SO 4 reveals a much slower protonation process since after 4 h of contact both NMS and HMS are present in the solution. The resultant protonated materials, H 2 x Mg 2 y - x Sn 4- y S 8 and H 4 x [(H y Na y -1 ) 1.33 x Sn 4--1.33 x ]S 8 , are themselves solid acids and readily react with and intercalate a variety of organic amines, where the band gap of the resultant adduct is influenced by amine choice and can be tuned within the range of 1.88(5)-2.27(5) eV. The work function energy values for all materials were extracted from photoemission yield spectroscopy in air (PYSA) measurements and range from 5.47 (2) to 5.76 (2) eV, and the relative band alignments of the materials are discussed. DFT calculations suggest that the electronic structure of Na 2 MgSn 3 S 8 and H 2 MgSn 3 S 8 makes them indirect gap semiconductors with multi-valley band edges, with carriers confined to the [MgSn 3 S 8 ] 2- layers. Light electron effective masses indicate high electron mobilities.

Methylammonium lead iodide (MAPbI 3 ) perovskite nanocrystals (NCs) offer desirable optoelectronic properties with prospective utility in photovoltaics, lasers, and light-emitting diodes (LEDs). Structural rearrangements of MAPbI 3 in response to photoexcitation, such as lattice distortions and phase transitions, are of particular interest, as these engender long carrier lifetime and bolster carrier diffusion. Here, we use variable temperature X-ray diffraction (XRD) and synchrotron-based transient X-ray diffraction (TRXRD) to investigate lattice response following ultrafast optical excitation. MAPbI 3 NCs are found to slowly undergo a phase transition from the tetragonal to a pseudocubic phase over the course of 1 ns under 0.02-4.18 mJ/cm 2 fluence photoexcitation, with apparent nonthermal lattice distortions attributed to polaron formation. Lattice recovery exceeds time scales expected for both carrier recombination and thermal dissipation, indicating meta-stability likely due to the proximal phase transition, with symmetry-breaking along equatorial and axial directions. These findings are relevant for fundamental understanding and applications of structure-function properties.

The aerobic photochemical oxidation of benzylamine was carried out on the ternary oxides CuWO 4 and BiVO 4 as a test proton-coupled-electron-transfer reaction in acetonitrile. Both oxides give the coupled imine product, N-benzylidenebenzylamine, in near quantitative (98-99%) yield, with rate constants of 0.34 h -1 g -1 and 0.70 h -1 g -1 for CuWO 4 and BiVO 4 , respectively.