High-level information encryption based on optical nanomaterials with multi-mode luminescence and dual-mode reading

Diverse phosphors have received widespread attention because of their ability to provide enhanced information security. However, these phosphors usually emit in the visible region and the emissions are discernible with human eyes, which, along with the single luminescence mode and reading manner, adversely affects the information security. This work exhibits a novel series of optical nanomaterials, Mg8Lu2Ge6O23:Bi3+/Yb3+/Ln (MLGB-Yb/Ln, Ln = Tm3+, Ho3+, and Er3+), with multi-mode luminescence and dual-mode reading characteristics and their suitability for information encryption is demonstrated. MLGB-Yb/Ln displays visible down-conversion luminescence, visible up-conversion luminescence (UCL), and invisible ultraviolet-B (UVB) persistent luminescence (PersL). The visible luminescence is directly detectable by human eyes (visible reading method); however, because the invisible UVB PersL cannot be perceived by human eyes, it can be used for information encryption. Interestingly, the encrypted information can be read by a charge-coupled device camera to decode the optical information (invisible reading method). More importantly, the unique optical properties ensure that MLGB-Yb/Ln behaves similarly to common UCL materials when viewed by humans, which further enhances the level of information encryption provided by invisible UVB PersL. Based on MLGB-Yb/Ln, we designed deceptive information encryption patterns to show the advantage of using these materials for information encryption.