Synthesis of ZnO nanoparticles-based fluorescent ink for information encryption and security applications

Luminescent ZnO nano pigments with a hexagonal structure were successfully synthesized using the hydrothermal method. The color fluorescent emission of ink can be tuned by hydrothermal conditions in the synthesis of pigment or by adjusting the pH values of the ink formulation. The ink formula based on luminescent ZnO nano pigments with a concentration of 15 % (w/w) was dispersed and homogenized in the vehicle, including water, PVA, and ethylene glycol. The stable ZnO nano ink formula has the zeta potential value of ξ = −24.8 mV at pH = 7.2, and ZnO pigments have an average particle size of about 500 nm in length and 90 nm in width. The logo samples printed on graphic paper and Couche paper with luminescent ink using a screen printing method show a bright yellow fluorescence at 565 nm under UV irradiation 365 nm and are invisible under normal light. The QR code on paper is readable by a smartphone under UV light. The ZnO nano ink is suitable for information encryption and anti-counterfeiting applications.