Undoped and Tl‐Doped Cs3Cu2I5 Thin Films as Potential X‐ray Scintillators

0D halide perovskite Cs 3 Cu 2 I 5 ‐based nanocrystals and bulk crystals are proven to be sensitive and efficient scintillators for X‐ray and γ‐ray detection. Herein, undoped and Tl‐doped Cs 3 Cu 2 I 5 microcrystalline films are synthesized by a thermal evaporation method. Both films crystallize into a Pnma space group of orthorhombic crystal lattice with preferred (004) growth orientation. The undoped Cs 3 Cu 2 I 5 thin film shows a sole emission peaking at 440 nm associated with the self‐trapped exciton emission. Doping of Tl + ions introduces another emission that peaks at 520 nm. The scintillation efficiency of both undoped and Tl‐doped Cs 3 Cu 2 I 5 thin films is about one‐third of that of CsI:Tl thin film with the same size and thickness. Within the first 5 s after X‐ray cutoff, afterglow signals of both the undoped and Tl‐doped Cs 3 Cu 2 I 5 thin films are over one order of magnitude lower than that of CsI:Tl thin film.