Grading patterning perovskite nanocrystal-polymer composite films for robust multilevel information encryption and decryption

Ensuring the concealment and integrity of the loaded information during delivery remains a key challenge to cryptography. In this study, we synthesized CsPbBr3 nanocrystals-polycarbonate composite films using the swelling-deswelling method, improved the stability and maintained the flexibility of the polymer. More importantly, we developed a novel patterning method using a nanosecond laser to engrave the composite selectively in three power grades: destroy the composite in high-power to present the patterns in bright field; damage the nanocrystals in medium-power to quench the fluorescence permanently; induce some defects to the nanocrystals in low-power to quench the fluorescence temporarily. A subsequent water immersion process allowed trace water penetration to passivate defects and recover the fluorescence locally to present the encrypted information. Our technology shows excellent performance by triple encryption level, convenient decryption (ultraviolet and water), low cost (2.8 x 10-3 USD/cm2) and high precision (minimum patterning size down to 15 mu m).