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.

Carbon nitrides synthesized by thermal polycondensation of melamine at 700 ℃ exhibit photoluminescence (PL) ranging from 400 to 650 nm. This broad PL is attributed to band to band transitions and bandtail transitions of lone pair (LP) states of intra-tri-s-triazine and inter-tri-s-triazine nitrogens. The proposed PL mechanism is further confirmed by diffusion reflectance spectroscopy, as well as time-resolved and temperature-dependent PL. This intense fluorescence is stable at different pH and resistant to UV exposure, suggesting that this inexpensive broadband luminescent material could be significant for whitelight-emitting (WLE) applications. Thus, quasi-WLE films and membranes with designed patterns are fabricated by embedding the carbon nitrides into polymethyl methacrylate. Moreover, even broader PL (400 to 740 nm) is acquired in composite films composed of carbon nitrides, further suggesting that the carbon nitrides are robust candidates for WLE.