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

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.