Synthesis and Characterization of ZnS:Mn Quantum Dots for Luminescent Security Ink Applications

Abstract

Mn-doped zinc sulfide quantum dots (ZnS:Mn QDs) were synthesized under ambient conditions using poly(vinyl alcohol) (PVA) as a stabilizing agent. The ZnS:Mn QD ink was subsequently prepared by dispersing the synthesized QDs into an aqueous PVA solution. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses confirmed that the ZnS:Mn QDs possessed a zinc-blende crystal structure and a nearly spherical morphology with an average particle size of approximately 12 - 15 nm. The optical properties of the QDs were characterized by ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) spectroscopy. The ZnS:Mn QDs exhibited a distinct absorption peak near 270 nm and a strong orange emission centered around 600 nm, corresponding to the ⁴T₁ → ⁶A₁ transition of Mn²⁺ ions. The QDs pigments were homogeneously dispersed in the PVA matrix using ultrasonic homogenization to formulate a photoluminescent ink. The resulting ZnS:Mn QD-based ink was applied onto graphic paper substrates by screen printing. Under λ ≈ 365 nm UV excitation, the printed patterns exhibited a bright orange emission around 600 nm, demonstrating the excellent luminescent properties and potential of the ZnS:Mn QDs ink for use in security printing applications.