Cs 4 PbX 6 (X = Cl, Br, I) Nanocrystals: Preparation, Water-Triggered Transformation Behavior, and Anti-Counterfeiting Application

As a promising material, Cs PbX (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 PbX NCs. It is found that the critical parameter for the formation of Cs PbX NCs is the ratio between Cs and Pb. Pure Cs PbX NCs are nonluminescent. The luminescence property of previous reported Cs PbX NCs may come from the impurity of luminescent CsPbX NCs. No coexistence of both Cs PbX and CsPbX phase has been found in one single nanoparticle. The water-triggered transformation from nonluminescent Cs PbX NCs to luminescent CsPbX NCs has been quantitatively studied. The potential application of Cs PbX NCs in humidity sensor and anticounterfeiting have been demonstrated. This work is important because it not only confirmed the nonluminescent nature of Cs PbX NCs but also demonstrated the potential application of such NCs.