Photoluminescence Enhancement of Perovskite Quantum Dot@Polymer Nanocomposite via Silver Epoxy Paste Treatment for Time-And Environment-Dependent Optical Encryption

In an increasingly digital and interconnected world, advanced information encryption techniques became imperative for ensuring the confidentiality, integrity, and availability of data. The integration of perovskite quantum dots (PQDs) with polymers has garnered considerable attention in the field of optical encryption for their eminent photoluminescence (PL) property and improved stability. Herein, we have designed a time- and environment-dependent optical encryption/decryption method based on the PL enhancement of CsPbBr₃ QD/polydimethylsiloxane (PDMS) nanocomposite film using a conductive Ag epoxy paste. Ag epoxy paste treatment was conducted by a thermal treatment subsequent to applying the Ag epoxy paste on the surface of nanocomposite film, followed by the removal of cured paste with ease. The Ag⁺ ions from the Ag epoxy paste diffuse into the PDMS matrix and passivate the surface defects of CsPbBr₃ QDs, resulting in enhanced PL properties (<i>e.g.,</i> intensity, lifetime, PL quantum yield (PLQY)) of the nanocomposite film.<br/>In order to enhance the image contrast for an optical encryption, surface defects have further been generated by ligand purification of CsPbBr₃ QDs during the synthesis of nanocomposite film. By controlling the treatment duration and external environment, Ag epoxy paste treatment was utilized as a time-dependent information encryption/decryption method via regulation of the PL intensity. Specifically, an encrypted information was initially concealed under daylight and disguised by a fake information under UV light, which was decrypted over time owing to the differences in the degradation rates of PQDs. Once the information had been confirmed by an intended receiver, the leakage of information was further avoided with a subsequent water immersion, in which the decrypted information permanently reverts to the initial fake information via PL intensity inversion between treated and untreated region. In this work, we propose novel applications of commercially available Ag epoxy paste as a method for surface defects passivation in PQDs embedded in polymer matrix and as a strategy for optical encryption/decryption, providing a high level of security with multiple encryption states and a straightforward decryption.