Dual Aliovalent Dopants Cu, Mn Engineered Eco-Friendly QDs for Ultra-Stable Anti-Counterfeiting

Doping in semiconductor quantum dots (QDs) using optically active dopants tailors their optical, electronic, and magnetic properties beyond what is achieved by controlling size, shape, and composition. Herein, we synergistically modulated the optical properties of eco-friendly ZnInSe₂/ZnSe core/shell QDs by incorporating Cu-doping and Mn-alloying into their core and shell to investigate their use in anti-counterfeiting and information encryption. The engineered "Cu:ZnInSe₂/Mn:ZnSe" core/shell QDs exhibit an intense bright orange photoluminescence (PL) emission centered at 606 nm, with better color purity than the undoped and individually doped core/shell QDs. The average PL lifetime is significantly extended to 201 ns, making it relevant for complex encryption and anti-counterfeiting. PL studies reveal that in Cu:ZnInSe₂/Mn:ZnSe, the photophysical emission arises from the Cu state via radiative transition from the Mn ⁴T₁ state. Integration of Cu:ZnInSe₂/Mn:ZnSe core/shell QDs into poly(methyl methacrylate) (PMMA) serves as versatile smart concealed luminescent inks for both writing and printing patterns. The features of these printed patterns using Cu:ZnInSe₂/Mn:ZnSe core/shell QDs persisted after 10 weeks of water-soaking and retained 70 % of PL emission intensity at 170 °C, demonstrating excellent thermal stability. This work provides an efficient approach to enhance both the emission and the stability of eco-friendly QDs via dopant engineering for fluorescence anti-counterfeiting applications.