Emerging Inkjet-Compatible Anti-Counterfeiting Inks Based on Microfluidic-Synthesized NIR PbS/CdS Quantum Dots

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Lead sulfide (PbS) quantum dots (QDs) exhibit promising near-infrared (NIR) emission properties.
• Core-shell PbS/CdS QDs offer enhanced stability and tunable optical characteristics via cation exchange.
• Industrial demand necessitates scalable synthesis methods for PbS/CdS QDs.

Purpose of the Study:

• To develop a microfluidic platform for the large-scale, controlled synthesis of PbS and PbS/CdS QDs.
• To produce stable, NIR-emissive inks from synthesized QDs for anti-counterfeiting applications.
• To demonstrate a covert optical security mechanism using NIR-emissive inkjet-printed materials.

Main Methods:

• Utilized a microfluidic device for precise control over synthesis parameters (flow rates, mixing, temperature, residence time).
• Synthesized PbS QDs with tunable wavelengths (1200-1600 nm) and PbS/CdS core-shell QDs via cation exchange (Pb²⁺ → Cd²⁺).
• Formulated an oily hydrophobic ink by dissolving QDs in octadecene-octane with polyethylene and assessed inkjet printability.

Main Results:

• Achieved highly monodisperse PbS and PbS/CdS QDs with consistent optical properties.
• PbS/CdS QD synthesis completed in 5 minutes, showing a 150 nm blue-shift and stable fwhm of 223 nm.
• Successfully printed invisible NIR emissive patterns using inkjet printers, detectable only under NIR imaging.

Conclusions:

• Microfluidic synthesis offers superior control for producing uniform QDs with desired optical properties.
• The developed NIR-emissive ink and printing method provide a novel, low-cost, high-security anti-counterfeiting solution.
• This covert optical security approach leverages NIR emission for advanced identification and authentication.