Generally, growing phase pure CsPbBr3 single crystals is challenging, and CsPb2Br5 or Cs4PbBr6 by‐products are usually formed due to the different solubilities of CsBr and PbBr2 in the single solvent. Herein, the growth of high‐quality phase pure CsPbBr3 perovskite single crystals at room temperature by a humidity controlled solvent evaporation method is reported first. Meanwhile, the room temperature phase transition process from three dimensional (3D) cubic CsPbBr3 to two dimensional (2D) layered tetragonal CsPb2Br5 and the detailed mechanism induced by humidity are revealed. Moreover, compared with the organic–inorganic perovskite, the prepared CsPbBr3 single crystals are much more stable under high humidity, which satisfies the long‐term working conditions of X‐ray detectors. The X‐ray detectors based on CsPbBr3 single crystals show a high sensitivity and a low detection limit of 1.89 μGyair s–1, all of which meet the needs of medical diagnosis.

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CsPbBR 3 PEROVSKITE SINGLE CRYSTALSHigh quality phase pure CsPbBr 3 perovskite single crystals are grown by solvent evaporation method under controlled humidity conditions. Meanwhile, the humidity is revealed as a key factor affecting the phase transformation of CsPbBr 3 at room temperature. Moreover, the prepared CsPbBr 3 single crystals are applied for the long-term working high performance X-ray detectors. More details can be found in article number 2103482 by Jingjing Chang and co-workers.

Doping engineering is necessary in the preparation of high-performance devices based on ultra-wide bandgap semiconductors. However, we do not yet understand the impurity level properties and their effects on performance modulation of transition metal doped α-Ga 2 O 3 . Here, using first-principles calculations with a hybrid functional, we find that I B and II B transition metal dopants exhibit relatively lower formation energies with a theoretically high hole concentration compared with Mg dopant. However, the induced acceptor levels are so deep that the impurity levels are transformed into AX centers. Although such AX centers hinder the formation of p-type conductivity, they can increase the optical absorption, ranging from deep ultraviolet to infrared regions. For electron-rich doped α-Ga 2 O 3 , the donor levels go from deep to shallow, then turn into deep levels again and finally to relatively shallow again as the transition metal dopant goes from group III B to VIII B of the periodic table. Because ionic bonds are formed between O and a dopant (IV B to V B ) with a raised d-orbital, covalent characteristics are observed for the O dopant (VI B to VIII B ) bonds with evident d-orbital splitting. These results add new insights into the impurity levels of α-Ga 2 O 3 , but also reveal potential applications of transition metal dopants in α-Ga 2 O 3 .