Reversible Transformation between Cs 3 Cu 2 I 5 and CsCu 2 I 3 Perovskite Derivatives and Its Anticounterfeiting Application.

Lead halide perovskites have promising values in photoelectronic and photovoltaic applications, but the toxicity of lead is a hard barrier. Copper halide perovskite derivatives (CHPDs), as a lead-free substitution of lead halide perovskites, also exhibit excellent photoelectric properties. Here, we present a facile one-step route for the synthesis of blue-emissive Cs 3 Cu 2 I 5 (emission at 440 nm) and yellow-emissive CsCu 2 I 3 (emission at 552 nm) CHPDs in ethanol at room temperature. Triggered by ethanol or CsI, a reversible chemical transformation accompanied by emissive color change between Cs 3 Cu 2 I 5 and CsCu 2 I 3 CHPDs was achieved. The reversible transformation mechanism was discussed, and this transformation was employed for effective anticounterfeiting.