In Situ Eu Redox in Cs₃YCl₆ Enabling Colorful Scintillators for Multicolor Radiography and Real-Time Dosimetry

Colorful scintillators with multilayer structures have attracted considerable attention for advanced radiography, but their layered architectures suffer from intrinsic interlayer excitation and photon crosstalk problems. Here, we design and report a single-phased Cs₃YCl₆:Eu³⁺ scintillator with tunable blue/red emissions via in situ x-ray-induced Eu³⁺ reduction. Partial transient reduction of Eu³⁺ with 4f→4f transition to Eu²⁺ with 5d→4f transition in Cs₃YCl₆ is attributed to low-lying defect states, confirmed by thermoluminescence and density functional theory calculations. Thanks to multicolor characteristics, the colorful Cs₃YCl₆:Eu³⁺ scintillator achieves x-ray dose real-time dosimetry within the range from 0.068 to 3.387 mGy, with a maximum relative sensitivity of 233.9% mGy^{- 1}. Furthermore, it exhibits multicolor x-ray imaging with a resolution of 10 lp mm^-1, allowing simultaneous material discrimination and x-ray dose dosimetry. This work provides a new design principle for the innovation of colorful scintillators and high-precision multicolor x-ray detection technologies.