Phosphonium‐Directed Synthesis of Tb/Eu Coordination Complexes for High‐Resolution X‐Ray Imaging

Enhancing the luminescence efficiency of scintillators is essential for achieving high‐performance x‐ray imaging; however, many existing materials face limitations, such as lead toxicity or insufficient light yield. Herein, we report a phosphonium salt‐directed strategy for synthesizing a novel coordination complex, Tb(phen) 2 Cl 3 (hereinafter referred to as TPC), and its europium‐doped derivative, Tb(phen) 2 Cl 3 : Eu (hereinafter referred to as TPC: Eu). We find that the ethyltriphenylphosphonium chloride additive is effective in suppressing rare‐earth ion hydrolysis and directing the growth of highly crystalline materials, as confirmed by control experiments. Doping with europium ions induces a substantial structural reorganization that optimizes the crystal field and enables an efficient Tb 3 + →Eu 3 + energy‑transfer pathway, as evidenced by concentration‑dependent lifetime variations and control experiments with the Eu‑only analog. This results in a near‐unity photoluminescence quantum yield of 97.41% and a long‐emission lifetime. Leveraging these superior luminescent properties, TPC: Eu functions as an efficient x‐ray scintillator with a high light yield (40 000 photons MeV −1 ), low detection limit, and excellent radiation stability. Furthermore, flexible composite films fabricated from this material enable high‐resolution x‐ray imaging capabilities. This work provides a viable crystal‐engineering approach for designing efficient, stable, and lead‐free scintillators, demonstrating their significant potential for applications in flexible and high‐resolution radiation detection.