Abstract
Recently, smart fluorescent materials, which respond to external stimuli, have attracted great attention and are widely used in the fields of information security and encryption. However, their drawbacks, such as low luminescence efficiency and complex processes, have strongly hindered industrial application. Here, we have developed lead halide perovskite nanocrystals/polymer composites as new intelligent fluorescent materials and exploited the novel fluorescence responsive mechanisms, to provide higher-level information security designs, which is expected to facilitate their commercialization in related fields.
Firstly, we have reported a challenging green in situ solvent engineering, to successfully synthesize lead halide perovskite nanocrystals/polymer composites with aqueous assistance. CH3NH3PbBr3/polyvinylidene fluoride (MAPbBr3/PVDF) powder derived from the air-dried novel precursor successively achieved impressive productivity (512 mg/mL), higher photoluminescence quantum yield (PLQY, 80%) and superb water resistance (< 3% decrease in 2 months). More surprisingly, green precursor engineering shows strong generalizability to a wide range of perovskite and polymers.
Then, a weak solvent engineering strategy based on perovskite nanocrystal/polymer composites is reasonably designed in the encryption and decryption applications of confidential information. By introducing and removing the weak solvent consisting of N,Ndimethylformamide (DMF) and water, the perovskite-based composite could be quenched and restored, resulting in reversible switching of the fluorescence signals. Surprisingly, this ON/OFF switch is highly effective in encrypting and decrypting various types of information.
Moreover, we have proposed a new strategy for high-level multi-modal encryption/decryption based on perovskite/polymer powders with homochromatic interference character. Two analogous perovskite/polymer powders have excellent optical properties and stability and can be used as mutual sources of interference in the encryption system, rendering their decipherment more challenging. The discovery of the respective characteristic stimulus source as the means of fluorescence recovery further constructs the confidential information system through multi-dimensional encryption and dynamic anti-counterfeiting.
Finally, we have successfully synthesized CHN2H4 (FA)-based/PVDF porous films with lowdimensional FAm+2PbmBr3m+2 perovskites inside. Water enters the film through the pores and decomposes the excess FABr, which converts the non-fluorescent FAm+2PbmBr3m+2 into fluorescent three-dimensional (3D) FAPbBr3, achieving the unique hydrochromic character of FA3.0/PVDF. Based on this, we have further developed the water-ink printing technology, and unclonable 3D fluorescent fingerprint imaging will contribute to the development and design of myriad innovations for data protection.