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Copper metal halides have emerged as a strong contender in the scintillator field due to the self‐trapped excitons (STEs) mechanism. However, their development has been hindered by the preparation process. Single crystals have long growth cycles and cannot achieve large areas and flexibility. Quantum dots have a low yield and can easily cause chemical pollution, and the thickness of films prepared by the spin coating cannot be controlled. To address these challenges, a new method for preparing Cs3Cu2Cl5 using sequential vacuum evaporation is developed. This allows successful preparation of large‐area (≈100 cm2) and flexible films. The STEs mechanism of Cs3Cu2Cl5 gives it unique properties such as a large Stokes shift that reduces self‐absorption effects, and a wide full width at half‐maximum that improves coupling with photodiodes. Therefore, Cs3Cu2Cl5 is applied to X‐ray imaging with a light yield of ≈30 000 photons MeV−1, a spatial resolution of over 10 lp mm−1, and a low detection limit below 0.8 µGyair s−1. In addition, the flexible Cs3Cu2Cl5 film enables effective dynamic imaging and clear imaging on non‐planar objects. It also exhibits good resistance to harsh environments, maintaining good imaging performance after 150 days. It is believed that sequential vacuum evaporation provides an important idea for preparing scintillators. [ABSTRACT FROM AUTHOR]

Real‐time in vivo detection of cancer via attenuation‐based plain X‐ray imaging is proposed to fundamentally overcome the penetration depth limits of current fluorescence‐based imaging techniques. Using cesium lead bromide (CsPbBr3, CPB) quantum dot (QD) scintillators, real‐time X‐ray detection of 5 mm‐sized Panc‐1 cell tumors grown in a mouse is successfully performed. The QDs are rapidly co‐synthesized and double‐encapsulated with silicon dioxide (SiO2) to completely prevent them from being aggregated, decomposed, or released; they are then conjugated with antibodies to target pancreatic cancer. Due to the dramatic X‐ray attenuation, the X‐ray signal from the CPB QDs placed under the 2 cm‐thick tissue is clearly observed, while their fluorescence signal is not detected at all. In in vivo mouse experiments, the injection of a tiny amount (2.8 μg on a QD basis) of the CPB–SiO2@SiO2–Ab nanoparticles gives rise to a bright spot at the location of the tumor. Cell viability assay and histological analysis confirm the biocompatibility and nontoxicity of the nanoparticles. [ABSTRACT FROM AUTHOR]