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

As a promising material, Cs₄PbX₆ (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 Cs₄PbX₆ NCs. It is found that the critical parameter for the formation of Cs₄PbX₆ NCs is the ratio between Cs and Pb. Pure Cs₄PbX₆ NCs are nonluminescent. The luminescence property of previous reported Cs₄PbX₆ NCs may come from the impurity of luminescent CsPbX₃ NCs. No coexistence of both Cs₄PbX₆ and CsPbX₃ phase has been found in one single nanoparticle. The water-triggered transformation from nonluminescent Cs₄PbX₆ NCs to luminescent CsPbX₃ NCs has been quantitatively studied. The potential application of Cs₄PbX₆ NCs in humidity sensor and anticounterfeiting have been demonstrated. This work is important because it not only confirmed the nonluminescent nature of Cs₄PbX₆ NCs but also demonstrated the potential application of such NCs.