Stable Core-Shell Structure Nanocrystals of Cs 4 PbBr 6 -Zn(moi) 2 Achieved by an In Situ Surface Reconstruction Strategy for Optical Anticounterfeiting.

Zero-dimensional Cs 4 PbBr 6 nanocrystals (NCs) possess attractive photoluminescence (PL) properties and feature facile chemical synthesis, making them promising for application in luminescent materials. However, Cs 4 PbBr 6 remains sensitive to polar solvents and thermal stimuli because of soft ionic nature of Cs 4 PbBr 6 and dynamic behavior of surface ligands. Herein, a strategy controlled by an in situ surface coordination reaction is developed to fabricate stable NCs with a Cs 4 PbBr 6 -Zn(moi) 2 core-shell structure. It was found that the Cs 4 PbBr 6 surface regulated by the use of 2-mercaptoimidazole (called moi) and the coordination between the -NH group of moi and Zn 2+ is critical for the formation of Cs 4 PbBr 6 -Zn(moi) 2 core-shell NCs. Meanwhile, the thickness of the Zn(moi) 2 shell can be facilely controlled by the growth time because of the solubility of moi and Zn(OAc) 2 ·2H 2 O in ethyl acetate. Compared to bare Cs 4 PbBr 6 , Cs 4 PbBr 6 -Zn(moi) 2 NCs exhibited highly improved polar solvent resistance and thermal stability. By combining the sensitivity of Cs 4 PbBr 6 and the stability of Cs 4 PbBr 6 -Zn(moi) 2 , we used two NCs as PL security inks to fabricate optical anticounterfeiting labels. Thus, the disposable or reusable optical anticounterfeiting label is achieved by changing the external dual-stimuli. This work provides a novel strategy to enhance the stability of Cs 4 PbBr 6 and develop its potential interest for application in anticounterfeiting technologies.