Thermally activated delayed fluorescence (TADF) X-ray scintillators have attracted increasing attention because of their theoretical ability to utilize 100% radiation-induced excitons. However, their scintillation performance is severely hampered by their typically low X-ray attenuation efficiencies or mechanochromic properties. Here, we demonstrate hybrid organic–inorganic TADF scintillators with remarkably high X-ray absorption cross sections based on non-mechanochromic Cu2X2 (X = Cl, Br, or I) nanoclusters. The Cu2X2 nanoclusters display radioluminescence light yields as high as 175 000 photons MeV–1, attributable to their low self-absorption and spatially separated HOMO and LUMO orbitals. Furthermore, because of their non-mechanochromic properties, these nanoclusters can be formed into scintillating screens with excellent radiation and humidity stability via soft-pressing. The fabricated TADF scintillating screens display a high X-ray imaging efficiency, benefiting from their high light yields and high spatial resolutions (∼30 lp mm–1). This work highlights the promise TADF Cu2X2 nanocluster-based scintillators have in meeting the demanding requirements of cutting-edge X-ray imaging.