Robust and Highly Efficient Rare‐Earth‐Based Zero‐Dimensional Hybrid Halides via Cerium Sensitized Terbium Emission

Rare‐earth ( RE ) hybrid metal halides (HMHs) have attracted considerable attention owing to their structural tunability and excellent luminescent properties. Here, N,N′‐ dimethylurea (DMU) was employed as a coordinating ligand to construct a new class of dual‐lanthanide‐site HMHs, [ RE (DMU) 6 ][ RE Cl 6 ] ( RE = Tb 3+ , Eu 3+ ), via mild solution synthesis and antisolvent diffusion. Single‐crystal X‐ray diffraction reveals that the structures consist of discrete [ RE (DMU) 6 ] 3+ cations and isolated [ RE Cl 6 ] 3− octahedra, forming zero‐dimensional molecular units. [Tb(DMU) 6 ][TbCl 6 ] and [Eu(DMU) 6 ][EuCl 6 ] exhibit characteristic green and red emissions from Tb 3+ and Eu 3+ , respectively. The Tb‐based compound also shows excellent resistance to thermal quenching, retaining about 91% of its emission intensity at 425 K relative to that at 100 K. Furthermore, Ce 3+ alloying in the Tb 3+ system effectively sensitizes the Tb 3+ emission through its broadband 5d→4f transitions, leading to a high photoluminescence quantum yield of 93.38%, among the highest reported for rare‐earth hybrid metal halides. This work enriches the family of rare‐earth hybrid metal halides and provides insight into their luminescence properties, thermal stability, and sensitized emission behavior.