Figure 4.

a) The X‐ray absorption coefficients of Cs₃Cu₂I₅, CsPbBr₃, CsI:Tl and carbon dots as a function of photon energy. The inset shows the photographs of colloidal solution of Cs₃Cu₂I₅ NCs under room light and X‐ray irradiation with the energy of 50 keV. b) The RL spectrum of NCs film under 50 keV X‐ray excitation and the curve of photon detection efficiency of SiPM. The inset shows the photograph of the Cs₃Cu₂I₅ film under X‐ray. c) The response intensity of Cs₃Cu₂I₅ NCs and CsPbBr₃ NCs as a function of X‐ray dose rate. The inset schematically shows the measurement, in which the NC films on glass are coupled with SiPM. d) Schematic of the prototype projection system for X‐ray imaging, and the sequence is an X‐ray source, a circuit board, Cs₃Cu₂I₅ NC scintillators and a smartphone camera. e) The photograph and f) the corresponding X‐ray image of a circuit board. g) Point spread function (red arrow in (f)) of the intensity profile is fitted with Gaussian function, and the FWHM is obtained as the spatial resolution. h) The photograph and i) X‐ray image of a universal board. j) The photograph and k) X‐ray image of a ball‐point pen with an encapsulated metallic spring.