Highly stable and tuneable-spectrum Pb2+-, Sb3+- and Ag+-doped Cs2KIn0.7Bi0.3Cl6 perovskite nanocrystals for anti-counterfeiting.

Abstract

Indium-based double perovskite nanocrystals (NCs) are promising for anti-counterfeiting applications but are hindered by poor air stability and limited colour tunability due to weak ligand binding and parity-forbidden transitions. Herein, we propose a favourable ligand binding strategy to synthesise Bi3+-doped Cs2KInCl6 NCs with enhanced stability and multicolour emission. Bi3+ doping induces local asymmetric coordination, increasing the number of surface active sites and strengthening ligand binding, which endows the NCs with exceptional air stability (>30 days). For color tuning, parity-forbidden transitions can be effectively broken by bandgap modulation and alloying in Pb2+-, Sb3+-, and Ag+-doped samples and Sb3+/Ag+ co-doped Cs2KInBi0.3Cl6. Strong electron-phonon coupling generates self-trapped exciton emissions, yielding blue (480 nm), green (525 nm), red (625 nm) and excitation-dependent yellow/red emissions. Furthermore, we demonstrate the fabrication of multicolour anti-counterfeiting patterns using these NCs via inkjet printing and screen printing. This work presents a viable pathway for developing stable, lead-free and multicolour perovskite nanomaterials for advanced anti-counterfeiting applications.