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X‐ray radiography, playing a crucial role in the daily life of humans, extends the application landscapes of perovskites. Lead halide perovskites remain superior candidates because of strong X‐ray absorption and effective conversion of X‐ray to visible photons. Unfortunately, the perovskites exhibiting efficient band‐edge emission (3D, quasi‐2D or 2D) usually suffer from severe self‐absorption, while the perovskites showing broadband emission with large Stokes shift (0D, 1D or 2D) usually have low quantum yield, long afterglow or poor solution‐processability. Halide‐intercalated perovskites, with incorporated halides in organic layers, exhibit attractive optoelectronic properties due to reduced confinement of excitons, but their development falls far behind due to limited molecular design strategies and wet‐chemistry methods. Here, the use of universal‐wet‐chemistry‐synthesized novel halide‐intercalated perovskites as an efficient X‐ray scintillator for X‐ray imaging is reported. These novel perovskites exhibit superior luminescence by exploiting both free and self‐trapped excitons via halide intercalation. Accordingly, such perovskite scintillators present higher radioluminescence performance compared with conventional perovskite scintillators through enhanced radiative recombination and suppressed self‐absorption simultaneously. With such a scintillator screen, high‐performance X‐ray imaging is demonstrated. The results not only represent a universal synthesis route for the development of perovskites, but also provide valuable guidance for high‐performance X‐ray radiography. [ABSTRACT FROM AUTHOR]

To study stability issues of three-dimensional perovskites, there is a strategy to introduce the thiocyanate ion (SCN - ) into CH 3 NH 3 PbI 3 (MAPbI 3 ) to solve these problems. Here, we report the bulk growth of layered perovskite MA 2 Pb(SCN) 2 I 2 single crystals by different growth methods in an ambient atmosphere. We also investigate the structural determination and refinements, band gap, and photoluminescence of MA 2 Pb(SCN) 2 I 2 single crystals. More importantly, the phase transition and stability of MA 2 Pb(SCN) 2 I 2 are systematically demonstrated. MA 2 Pb(SCN) 2 I 2 undergo the reversible single-crystal to single-crystal phase transition in the orthorhombic systems from the space group Pmmn (no. 59) to the space group Pmn 2 1 (no. 31) at low temperature. Moreover, the temperature-dependent recovery behaviors of MA 2 Pb(SCN) 2 I 2 single crystals, powders, and thin films at high temperature are studied in detail. Besides, the moisture stability of MA 2 Pb(SCN) 2 I 2 is described when exposed to moisture condition by the experiment and theoretical calculations. It would be interesting to not only conduct a comprehensive study on the crystal structures and the phase transition processes of layered perovskites but also provide guidance for further optoelectronic applications of these perovskite materials.