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 P-3(0,1) -> S-1(0) 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.