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Long‐lasting radioluminescence scintillators have recently attracted substantial attention from both research and industrial communities, primarily due to their distinctive capabilities of converting and storing X‐ray energy. However, determination of energy‐conversion kinetics in these nanocrystals remains unexplored. Here we present a strategy to probe and unveil energy‐funneling kinetics in NaLuF4:Mn2+/Gd3+ nanocrystal sublattices through Gd3+‐driven microenvironment engineering and Mn2+‐mediated radioluminescence profiling. Our photophysical studies reveal effective control of energy‐funneling kinetics and demonstrate the tunability of electron trap depth ranging from 0.66 to 0.96 eV, with the corresponding trap density varying between 2.38×105 and 1.34×107 cm−3. This enables controlled release of captured electrons over durations spanning from seconds to 30 days. It allows tailorable emission wavelength within the range of 520–580 nm and fine‐tuning of thermally‐stimulated temperature between 313–403 K. We further utilize these scintillators to fabricate high‐density, large‐area scintillation screens that exhibit a 6‐fold improvement in X‐ray sensitivity, 22 lp/mm high‐resolution X‐ray imaging, and a 30‐day‐long optical memory. This enables high‐contrast imaging of injured mice through fast thermally‐stimulated radioluminescence readout. These findings offer new insights into the correlation of radioluminescence dynamics with energy‐funneling kinetics, thereby contributing to the advancement of high‐energy nanophotonic applications. [ABSTRACT FROM AUTHOR]

Colloidal nanocrystal scintillators hold great potential in fabricating large-area, flexible X-ray detectors for high-resolution X-ray imaging of highly curved, irregularly shaped objects. The synthesis of high-efficiency, high-stability nanoscintillators is of great importance for the development of X-ray imaging detectors. In this study, we develop a class of cerium (Ce3+)-sensitized core-shell nanoscintillators that are suitable for achieving flexible X-ray luminescence imaging. We demonstrate that an epitaxial growth of NaGdF 4 :Ce(60%) on the surface of NaGdF 4 :Eu(15%) nanoscintillators as a sensitization layer allows for enhancing X-ray-induced radioluminescence. We reveal that the enhancement of X-ray luminescence in nanoscintillators could be attributed to the synergistic effect of high-Z composition-induced X-ray absorption, Ce3+ sensitization, and surface passivation to relieve energy quenching. By incorporating the nanoscintillators into a flexible elastomer of polydimethylsiloxane (PDMS), we demonstrate its utility in high-resolution flexible X-ray luminescence imaging. • A class of Ce3+-sensitized nanoscintillators with efficient X-ray luminescence were synthesized. • An energy transfer mechanism for X-ray luminescence in NaGdF 4 :Eu@NaGdF 4 :Ce core-shell nanoscintillators was proposed. • High-resolution flexible X-ray luminescence imaging was achieved by embedding nanoscintillators into a PDMS elastomer. [ABSTRACT FROM AUTHOR]