Isothermal Near‐Room‐Temperature Growth of Mechanically Robust Cs ₃ Cu ₂ I ₅ Single Crystals for Gamma‐Ray Detection and X‐Ray Imaging

ABSTRACT Cs 3 Cu 2 I 5 is a lead‐free, zero‐dimensional inorganic perovskite noted for its low toxicity, excellent stability, and outstanding optical properties, making it a promising scintillator. Large Cs 3 Cu 2 I 5 single crystals are attainable by solution‐ or melt cooling; however, thermal stress associated with temperature changes often degrades processing yield and crystal quality. Here, we report the growth of large Cs 3 Cu 2 I 5 single crystals (≈3 cm) using a settled temperature and controlled antisolvent diffusion method. The isothermal near‐room‐temperature growth condition eliminates thermal stress and improves mechanical robustness. The as‐grown crystals are readily machined into wafers with high structural integrity, evidenced by a narrow rocking curve FWHM of 20.6″. Cs 3 Cu 2 I 5 single‐crystal wafers used for γ‐ray detection to multiple sources ( 1 3 7 Cs, 2 4 1 Am, 6 0 Co, and 2 2 Na) exhibit outstanding scintillation performance, including a high light yield of 67 500 ph/MeV and an energy resolution of 4.4% ( 1 3 7 Cs). Furthermore, Cs 3 Cu 2 I 5 crystal wafers were utilized as an x‐ray imaging screen, achieving a spatial resolution of 19.3 lp/mm at an MTF of 0.2. The developed technique promotes Cs 3 Cu 2 I 5 crystals toward ready‐for‐use applications.