Excitation-Dependent Photoluminescence of Undoped Bimetallic Halides with Dual Emitting Centers for Optical Anticounterfeiting Application

Excitation-dependent (Ex-De) photoluminescence, characterized by distinct emission color changes under varying excitation wavelengths, has been extensively investigated in doped systems, where luminescence relies on a dopant–host synergy. However, Ex-De behavior achieved through two independent luminescent centers in undoped metal halide lattices has scarcely been reported. Herein, we synthesized two novel zero-dimensional (0D) bimetallic halides (BMHs), [Eu(UREA) 7 H 2 O][SbCl 6 ] ( Eu–U ) and [Tb(UREA) 7 H 2 O][SbCl 6 ] ( Tb–U ), via a cooling crystallization method. Structural analyses reveal that Eu 3+ /Tb 3+ ions coordinate with UREA and water molecules to form cationic complexes [Eu(UREA) 7 (H 2 O)] 3+ /[Tb(UREA) 7 (H 2 O)] 3+, which isolate [SbCl 6 ] 3– anions. Hirshfeld surface analysis further indicates substantial hydrogen bonding between the complex cations and [SbCl 6 ] 3– octahedra, leading to notable structural distortion. Spectroscopic studies confirm that both compounds can exhibit simultaneous broadband emission from Sb 3+ and narrowband emission from Eu 3+ /Tb 3+, with no energy transfer between the centers. Leveraging this unique Ex-De behavior, we fabricated anticounterfeiting patterns by embedding Eu–U and Tb–U in silicone, demonstrating effective information concealment and retrieval. This work not only enriches the family of BMHs but also realizes synergistic narrowband and broadband emission, offering new insights for designing Ex-De luminescent materials with independent dual emitting centers.