Tailoring the Emission Properties of Cs2NaLuCl6 for Anti‐Counterfeiting, X‐Ray Scintillation, and Night Vision Applications

Abstract The ever‐increasing counterfeiting issues have triggered a research upsurge in multi‐modal fluorescence anti‐counterfeiting materials. All inorganic metal halide double perovskites possess the advantages of facile preparation procedures and high thermal stability, which also provide suitable doping sites to regulate the emission behavior and highlight the potential for serving as multi‐modal fluorescence anti‐counterfeiting materials. Herein, a series of Sb 3+ , Er 3+ , and Yb 3+ solely or codoped Cs 2 NaLuCl 6 are successfully prepared, and the optical properties are dependent on the doping ratio of Sb 3+ and lanthanide ions (Ln 3+ ). Notably, due to the participation of energy‐transfer and cross‐relaxation processes, the tri‐doped Cs 2 NaLuCl 6 (0.3%Sb 3+ ‐20%Er 3+ ‐50%Yb 3+ ‐Cs 2 NaLuCl 6 ) shows luminescence responses to the excitation sources with different photon energies, which is employed to construct anti‐counterfeiting fluorescence patterns by combining the Sb 3+ , Er 3+ , and Yb 3+ solely or codoped Cs 2 NaLuCl 6 . Besides the multi‐modal luminescence behavior, NIR emission from Er 3+ and Yb 3+ can be used in the night‐vision device. Remarkably, the 20%Er 3+ ‐doped Cs 2 NaLuCl 6 shows an excellent light yield of 30767 photons MeV −1 and low limit of detection (LoD) of 108 nGy s −1 , highlighting the potential in X‐ray imaging. This work provides a rational route to design multi‐functional materials that can be used in anti‐counterfeiting, night vision, and X‐ray imaging.