High-Triplet-Energy Ancillary-Ligand Regulation of Dual-Antenna Eu(III) Scintillators: Near-Unity PLQY for 3D X-Ray...

Eu(III) complex scintillators, benefiting from efficient triplet-exciton utilization and strong x-ray absorption, are promising candidates for advanced x-ray detection and imaging. However, current design strategies for dual-antenna Eu(III) complex scintillators primarily prioritize low-triplet-energy primary ligands, whereas the energetic and mechanistic roles of high-triplet-energy ancillary ligands remain insufficiently explored. Herein, we present a systematic study on ancillary-ligand-regulated scintillation in dual-antenna Eu(III) complex scintillators. Using dibenzoylmethane (DBM) as the primary ligand and three high-triplet-energy arylphosphine oxides as ancillary ligands, a series of Eu(DBM)₃(L) complexes (L = Dpepo, Xpo, Dppbo) were constructed. Among them, Eu(DBM)₃(Dppbo) exhibits a near-unity photoluminescence quantum yield of 98.5% and an ultrahigh relative light yield of 61737 photons MeV^-1. This outstanding performance arises from triplet-energy matching between the Dppbo and DBM that enhances ligand-ligand charge transfer, together with increased ligand rigidity and ordered π-π stacking that suppresses nonradiative decay and facilitates charge-carrier transport. Furthermore, Eu(DBM)₃(Dppbo) was embedded into a styrene-ethylene-butylene-styrene elastomer to afford a large-area stretchable scintillation film, delivering > 30 lp mm^-1 in static x-ray imaging and enabling advanced x-ray videography, including 3D dynamic, underwater, and stretchable imaging. These findings establish ancillary-ligand engineering as a general molecular design strategy for achieving highly efficient Eu(III) complex scintillators.