Photochromic Cs ₂ Pb(NO ₃ ) ₂ Br ₂ Perovskite Nanosheets as a Novel Anti‐Counterfeiting Material

Although the photoinduced segregation phenomenon of mixed halide perovskites has application potential in the fields of anti-counterfeiting and information storage, the easy oxidation of I^- into highly volatile I₂ leads to a serious deficiency in material stability. In this study, we addressed this issue by substituting the instable anion of I^- with the stable anion of NO₃ ^- and synthesizing a novel photochromic 2D perovskite of Cs₂Pb(NO₃)₂Br₂ nanosheets (PNSs). The synthesized functional material exhibited significantly enhanced stability, maintaining stable luminescence under ambient conditions for over a year, far surpassing traditional mixed halide perovskites. Further research revealed that reversible photoluminescence switching between orange and green in Cs₂Pb(NO₃)₂Br₂ PNSs suspension could be achieved by regulating the UV light power of irradiation and solution concentration, demonstrating the photoinduced segregation phenomenon in non-halide/halide hybrid perovskites. The photoinduced segregation could be effectively suppressed by doping with Cl^- ions. Based on this photochromic property, we designed a novel anti-counterfeiting label by exploiting the distinct UV-response characteristics of Cs₂Pb(NO₃)₂Br₂ and Cs₂Pb(NO₃)₂Br_2-xCl_x, offering a new design strategy for stimulus-responsive perovskite materials.