The increasing demand for high-speed X-ray imaging requires scintillators with high light yield and fast response. Perovskite nanocrystals are promising candidates due to their distinctive optical properties and solution processability. However, the fabrication of thick X-ray films, which are several orders of magnitude thicker than conventional optoelectronic devices, leads to severe material waste and reduced light yield caused by strong spectral overlap and self-absorption. In addition, conventional synthesis methods often suffer from low reaction yields and uncontrolled exciton pathways. Here, we develop a low-temperature polar-solvent synthesis method that achieves a reaction yield of 162 mg mL−1 and optimizes exciton routing for improved energy transfer. This approach increases the Stokes shift and reduces the radioluminescence decay to 7.19 ns. Consequently, high-speed X-ray imaging at 7,680 frames per second with a spatial resolution of 27.6 line-pairs per millimeter is achieved, supporting sustainable commercialization of perovskite nanocrystal scintillators for dynamic X-ray imaging.