Processing luminescent metal halide microcrystals into counterpart nanocrystals (NCs) can rationally enhance the resolution in X-ray scintillation imaging. It remains a challenge for the controlled synthesis of the hybrid NC luminescence materials, which is important for the fabrication of the organic films. Herein, we design the synthesis of copper(I)-based halide Cu 6 I 8 (bu-ted) 2 (Cu 6 I 8 C 20 H 42 N 4 ) (bu-ted: 1butyl-1,4-diazabicyclo [2.2.2] octan-1-ium) NCs via a surfactant-assisted method utilizing surface tension to limit the crystal size. Cu 6 I 8 (bu-ted) 2 NCs with prominent near-to-unity photoluminescence quantum yield results in ultrahigh light output that is calculated to be 480% of a commercial Lu 3 Al 5 O 12 :Ce 3+ scintillator with a low detection limit of 32 nGy/s. X-ray imaging with a spatial resolution of 17 lp mm −1 is demonstrated based on the fabrication of large-area Cu 6 I 8 (bu-ted) 2 composite scintillation screens. This study provides a foundation method to nanocrystallize the copper(I)-based hybrid halide scintillators for prominent X-ray imaging.