Multimodal Luminescence in an Excellent Stable Single-Host Nanocrystal by Leveraging Self-Trapped States and Shallow Defect Levels for Advanced Anticounterfeiting and Encryption

Integrating enough luminescent modes into a single-host nanomaterial with high stability is crucial for advanced anticounterfeiting and information encryption technologies, but it remains a challenge. Herein, Mn²⁺-doped Cs₂NaYbCl₆ double perovskite nanocrystals (NCs) have been successfully synthesized by a modified hot-injection method and exhibited extraordinary multimodal luminescence. Under different stimuli, the NCs demonstrate diverse optical responses, including dual-color downshifting luminescence under ultraviolet (UV) light and X-ray excitation, persistent luminescence (PersL), and temperature-dependent multicolor luminescence. These processes can be completed in single-host NCs due to the harmonious coordination of self-trapped exciton states (STEs), ⁴G and ⁴D energy levels of Mn²⁺ ions, and inherent shallow defects of the host. Moreover, the observed PersL originates from shallow defects induced by Mn²⁺ occupying Yb³⁺ sites and intrinsic chlorine vacancies, which create efficient trap states for energy storage and release. Beyond its multifaceted luminescence, the developed NCs also showcase exceptional environmental stability, and they can maintain good optical properties even after being stored in the air for more than half a year. Furthermore, the high-level anticounterfeiting and encryption based on the NCs have been implemented, showing that this material is a highly promising candidate for commercial security applications.