Triplet Excitons Harvesting in Organometallic [Cu(P^P)(N^N)] ⁺ Scintillators Toward Highly Resolved and Robust X‐Ray Imaging

Organic scintillators have attracted great attention in the fields of medical imaging, radiotherapy, and non‐destructive testing. However, most of the organic scintillators suffer from low exciton utilization and severe thermal quenching. Herein, we report a series of high‐temperature‐adaptive scintillators based on semi‐cage organometallic [Cu(P^P)(N^N)] + complexes. Through a synergistic molecular design combining Cu(I)‐moderated spin–orbit coupling to enable efficient reverse intersystem crossing (RISC) and rigid molecular configuration to suppress non‐radiative decay, these complexes exhibit thermally activated delayed fluorescence and radioluminescence activity. The optimized Cu‐p‐Br delivers a high light yield of 28 348 photons MeV −1 and excellent thermal quenching resistance. Remarkably, the radioluminescence intensity at 383 K still maintains 76% of that at room temperature. We further demonstrate its capability for high‐resolution x‐ray imaging under both ambient and high‐temperature conditions. This work not only presents a class of efficient organometallic scintillators with exceptional thermal robustness but also establishes a design framework integrating electronic and steric control for developing thermally stable thermally activated delayed fluorescence materials, thereby advancing scintillator technology toward demanding real‐world environments.