Dopant Diffusion Equilibrium Overcoming Impurity Loss of Doped QDs for Multimode Anti‐Counterfeiting and Encryption

Abstract High ion diffusivity of Cu⁺ dopants accelerates outdiffusion in quantum dots (QDs) at high temperatures. This kind of self‐purification gives rise to a sharp decrease in dopant photoluminescence (PL) intensity. Herein, a dopant diffusion equilibrium strategy is developed by introducing extra Cu⁺ in the epitaxial growth process. By preventing the loss of dopant Cu⁺, both the decrease of dopant PL and increase of band‐edge PL intensity are successfully suppressed. The coexistence of visible and invisible near‐infrared (NIR) PL bands for Cu‐doped CdSe@CdS QDs demonstrates their novel multimode anti‐counterfeiting/encryption potential. Via printing by combined using of intrinsic and doped QD “inks” with visible and invisible NIR emissions, respectively, the bulk‐sized patterns, texts, and numerals can achieve visible–invisible PL synergetic confidential information multimode anti‐counterfeiting and encryption.