Five-level anti-counterfeiting based on versatile luminescence of tri-doped double perovskites

Luminescent materials with multi-emission features are difficult to be replicated, which are highly desirable for advanced anti-counterfeiting. Here, we report the pioneering synthesis of Mn²⁺/Yb³⁺/Er³⁺ tri-doped Cs₂Ag_0.8Na_0.2InCl₆ double perovskites (MYE-DP), which exhibit photoluminescence (PL) covering from visible to near-infrared (NIR). The PL colors under excitations of 254 and 365 nm are notably different due to the changed relative emission intensities of self-trapped excitons (STEs) and Mn²⁺ d–d transition. Moreover, under the excitation of a NIR laser, the MYE-DP exhibits upconversion (UC) emissions of Mn²⁺ and Er³⁺. After ceasing the excitation, the long-lived trapped electrons can be thermally released to Mn²⁺ and Er³⁺ ions, resulting in both visible and NIR afterglow. Based on multi-modal emissions of the MYE-DP, we demonstrate a five-level anti-counterfeiting strategy, which significantly increases the anti-counterfeiting security. In addition, this work provides valuable insights into the energy transfer between STEs, Mn²⁺, Ln³⁺, and traps, laying a solid foundation for future development of new lead-free perovskites.