Competitive Phase Transition of NaYS ₂ in Non‐Vacuum Environment for Cutting‐Edge Anti‐Counterfeiting

Abstract Recently, chalcogenides with layered structures exhibit promising applications in the fields of information chaos processing and compilation remodeling, yet facile synthesis of their microcrystals with multi‐temporal and multi‐modal luminescence remains a major challenge. Herein, a competitive phase transition to generate orderly layered NaYS ₂ microcrystals is achieved by lattice reconstruction with introduction S ²⁻ occupying a unique anionic site in non‐vacuum sulfur‐rich environment, revealing crucial role of competitive phase transitions in regulating material structure and properties. Simultaneous photoinduced luminescent chromism and photo‐stimulated luminescence are attained by introducing Pr ³⁺ . Interestingly, broadband long‐wavelength visible afterglow emission in 4f ¹ 5d ¹ cluster state is achieved and a reversible temporary change in upconversion emission from orange broadband to green narrowband occurs under continuous 980 nm excitation, which is attributed to ordered polarization of Pr ³⁺ in YS ₆ layer and injection of defects. Furthermore, by integrating long‐lived down‐conversion emission and relatively short‐lived up‐conversion emission in Pr ³⁺ ‐doped NaYS ₂ , a multilevel dynamic optical anti‐counterfeiting platform is constructed based on transient and long afterglow luminescence. This work implements a competitive phase transition to generate NaYS ₂ with 2D structure, providing a new model of tunable space‐time resolved emission for spatiotemporal optoelectronic multiplexing, which are applicable to large‐capacity information encryption, optical data storage, and biosensing.