Cs4PbX6 (X = Cl, Br, I) Nanocrystals: Preparation, Water-Triggered Transformation Behavior, and Anti-Counterfeiting Application

As a promising material, Cs 4 PbX 6 (X = Cl, Br, I) nanocrystals (NCs) have attracted much attention. However, their luminescent property is still under debate. In this work, we first systematically studied the colloidal preparation of Cs 4 PbX 6 NCs. It is found that the critical parameter for the formation of Cs 4 PbX 6 NCs is the ratio between Cs and Pb. Pure Cs 4 PbX 6 NCs are nonluminescent. The luminescence property of previous reported Cs 4 PbX 6 NCs may come from the impurity of luminescent CsPbX 3 NCs. No coexistence of both Cs 4 PbX 6 and CsPbX 3 phase has been found in one single nanoparticle. The water-triggered transformation from nonluminescent Cs 4 PbX 6 NCs to luminescent CsPbX 3 NCs has been quantitatively studied. The potential application of Cs 4 PbX 6 NCs in humidity sensor and anticounterfeiting have been demonstrated. This work is important because it not only confirmed the nonluminescent nature of Cs 4 PbX 6 NCs but also demonstrated the potential application of such NCs.