Ion-Exchanging Lead-Free Perovskite with Tunable Emission Wavelengths for Chemical and Fluorescent Double-Modal Anticounterfeiting Application.

Abstract

Novel and covert fluorescence is quite desirable for fluorescent anticounterfeiting application. Here, Cs2InCl5·H2O/Sb and Cs2NaInCl6/Sb with high photoluminescence quantum yields (PLQYs) of 99.61 and 99.9%, respectively, were achieved. Considering the excellent optical performances together with the high similarity of the two crystal structures, we tried to realize the crystal structure transition from Cs2InCl5·H2O/Sb to Cs2NaInCl6/Sb by an ion-exchange method. It was well done by just adding the NaCl precursor with different concentrations in the Cs2InCl5·H2O/Sb product. Interestingly, a gradual color change from yellow to orange, warm white, white, cool white, and blue was achieved in the process of crystal structure transition. The energy-transfer dynamic models of Cs2InCl5·H2O/Sb, the white product, and Cs2NaInCl6/Sb were identified. The chemical reaction and UV fluorescence properties made it possible for application in chemical and fluorescent double-modal anticounterfeiting and highly decreased the possibility of being cracked and copied. Especially, when salt for daily cooking was used to replace NaCl, a similar phenomenon happened as that of the 99.9% NaCl precursor, which made it easy to be applicated. The combination of chemical and optical verifications provides two levels of security and unbreakable encryption. The results demonstrate that the transition from Cs2InCl5·H2O/Sb to Cs2NaInCl6/Sb is highly promising in fluorescent anticounterfeiting application.