Surface Coating of Lead-free Perovskites to Break the Luminescence Threshold for Fluorescent Information Recognition

Lead-free perovskites are becoming a promising candidate in the new generation of fluorescence information recognition owing to their superior optoelectronic properties and stable chemical properties. However, the vast majority of perovskite phosphors present a luminescence threshold (LT) due to concentration quenching and exhibit a single luminescent peak as the monochrome source, leading to limited application prospects. Herein, surface coating of Bi³⁺-doped all-inorganic lead-free Cs₂ZrCl₆ perovskite microcrystal is designed to break LT and present dual-mode luminescence under 259 and 358 nm excitation. Dual-mode fluorescence peaks are located at 435 and 453 nm, contrary to self-trapped exciton (STE) emissions reported previously, which originate from STE emission and inter-configurational ³P_0,1 → ¹S₀ transitions of Bi³⁺, respectively. Moreover, surface coating of ethyl orthosilicate (CHSiO) is introduced to form a core-shell structure, enhancing the particle dispersion and the luminescence stability of Cs₂ZrCl₆:Bi³⁺ phosphors, which breaks the LT to increase luminescence intensity. Finally, the Cs₂ZrCl₆:Bi³⁺-coated CHSiO is mixed with polydimethylsiloxane and printed QR code by screen printing technology to achieve dual-mode luminescence and display. These findings reveal the unique advantages of surface-coated Bi³⁺-doped Cs₂ZrCl₆ perovskites, thus opening a new pathway for multi-mode fluorescence recognition and remote excitation applications.