Highly luminescent all-inorganic lead-free AgInS2/ZnS QDs for multicolor and multistage anti-counterfeiting and encryption

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We describe the design and synthesis of eco-friendly AgInS 2 /ZnS QDs via a facile one-pot synthesis method for application in encryption and anti-counterfeiting. A significant enhancement in PLQY (up to 45 ​%) and stability are observed with increased ZnS shell thickness. By varying the Ag:In composition from 1:2 to 1:0.25, the PL emission of AgInS 2 /ZnS QDs can be tuned from the visible to NIR (up to 900 ​nm). The ink fabricated with AgInS 2 /ZnS QDs shows greater thermal and water stability compared to AgInS 2 QDs. The patterns printed with these luminescent inks show excellent water and thermal stability and the capability to print on surfaces of any type and color, making them promising for practical use. These printed patterns are completely transparent/invisible in normal light and visible under 254 ​nm, 365 ​nm and 464 ​nm (blue LED) illumination. These features offer rapid responsive and multi-layered information encryption, and sophisticated anti-counterfeiting.