Double-Key Optical Information Encryption Enabled by Multi-State Excitation-Emission of Mn-Doped Metal Chlorides

Given the paramount importance of information security and confidentiality, various optical information encryption (OIE) strategies are developed based on luminescence. However, the protected information usually can be decrypted, and there is a lack of high-level security because only one protection key can be applied. Herein, a double-key OIE strategy is developed based on multi-state excitation-emission of Mn-doped metal chlorides (MMCs). The information delivered by different MMCs can be encrypted based on the similar orange luminescence of Mn d-d transition. The distinguishable excitation conditions, switchable luminescence, and unique afterglow in MMCs enable new encryption mechanisms with a great potential for high confidentiality multi-key encryption. It is demonstrated that four information channels can be encrypted into a single luminescent pattern, concealing the true information by three interference messages, which greatly increases the security. As a demo, an encrypted quick response (QR) code is created, which can only be decrypted with both the "excitation wavelength key" and "capture time key." The double-key mechanism enhances the level of security and confidentiality without using expensive equipment or external stimuli.