Rare earth doped double perovskite nanocrystals with controllable emission wavelength and model for high-level anti-counterfeiting

Fluorescent anti-counterfeiting technology has become one of the most commonly used anti-counterfeiting technologies because of its simple preparation, low cost and high safety. However, there are still some key technical problems to be solved in developing multi-mode and polychromatic fluorescent materials for high-level anti-counterfeiting. Herein, Yb3+/Er3+ codoped Cs2AgIn0.99Bi0.01Cl6 double perovskite nanocrystals (DPNCs) with dual-mode polychromatic emission were developed. Under the irradiation of 365 nm ultraviolet (UV) light, the DPNCs emitted a bright downshifting (DS) yellow light, which comes from the self-trapping excitons (STEs) recombination. While the DPNCs produced upconversion (UC) green fluorescence under the 980 nm laser excitation, which is attributed to the transitions of 2H11/2 -> 4I15/2 and 4S3/2 -> 4I15/2 of Er3+ ions. In view of its dual-mode and polychromatic fluorescence characteristics, a high-level anti-counterfeiting based on this fluo-rescent material is designed. Moreover, the brightness of the anti-counterfeiting pattern based on this material decreases very little after three months. These results indicated that the dual-mode and polychromatic DPNCs reported have potential application in information encryption and identity recognition.