Ligand Engineering for Ultrahigh-Light-Yield Lanthanide Complex Scintillators

Scintillators featuring high light yield and low detection limit are critically important for high-energy radiation detection. Lanthanide complexes are attractive candidates due to their strong X-ray absorption, facile synthesis, and high photostability. However, their practical application has long been hindered by relatively low light yield. Here, we show that ligand engineering is a general and effective strategy for realizing lanthanide complex scintillators with ultrahigh light yield. By precisely tuning the π-conjugation extent of the β-diketone ligands across a rationally designed series of Tb(β-diketone)3·2H2O complexes, we identify Tb(acac)3·2H2O as an exceptional scintillator, whose exciton utilization efficiency is near-unity (99.3%). Under X-ray excitation, polycrystalline Tb(acac)3·2H2O delivers a light yield of 134,400 photons/MeV, which further increases to an unprecedented 180,000 photons/MeV in its single-crystal form. Ultrafast spectroscopic investigations directly reveal the underlying energy transfer mechanism of lanthanide complexes, highlighting the decisive role of the energy gap between ligand triplet states and lanthanide excited states, and establishing a broadly applicable ligand-engineering design principle for developing highly efficient lanthanide complex scintillators. We further demonstrate the practical utility of ultrahigh-light-yield Tb(acac)3·2H2O in X-ray intensifying screens, enabling at least a fivefold reduction in irradiation time compared with radiography performed without an intensifying screen. Overall, these results establish ligand engineering as a powerful paradigm for molecular scintillator design and open new opportunities for advanced radiation detection and imaging technologies.