X-ray　scintillators　are　widely　used　in　medical　imaging,　industrial　flaw　detection,　security　inspection,　and　space　exploration.　However,　traditional　commercial　scintillators　are　usually　associated　with　a　high　use　cost　because　of　their　substantial　toxicity　and　easy　deliquescence.　In　this　work,　an　atomically　precise　Au-Cu　cluster　scintillator　(1)　with　a　thermally　activated　delayed　fluorescence　(TADF)　property　was　facilely　synthesized,　which　is　environmentally　friendly　and　highly　stable　to　water　and　oxygen.　The　TADF　property　of　1　endows　it　with　an　ultrahigh　exciton　utilization　rate.　Combined　with　the　effective　absorption　of　X-ray　caused　by　the　heavy-atom　effect　and　a　limited　nonradiative　transition　caused　by　close　packing　in　the　crystal　state,　1　exhibits　an　excellent　radioluminescence　property.　Moreover,　1　has　good　processability　for　fabricating　a　large,　flexible　thin-film　device　(10　cm　×　10　cm)　for　high-resolution　X-ray　imaging,　which　can　reach　40　μm　(12.5　LP　mm-1).　The　properties　mentioned　earlier　make　the　coinage　metal　cluster　promising　for　use　as　a　substitute　for　traditional　commercial　scintillators.　©　2023　The　Authors.　Published　by　American　Chemical　Society.