Elaboration and Investigation on Photoluminescence Enhancement of Poly (Vinyl Alcohol) Mn2+ Doped ZnS Quantum Dots for Security Ink Applications

Quantum dots (QDs) ink from Mn2+-doped ZnS (ZnS:Mn2+) quantum dots with poly(vinyl alcohol) (PVA) as stabilizer has been synthesized by two steps. First, ZnS:Mn2+ quantum dots were prepared by chemical co-precipitation method at room temperature and second, the powder of ZnS:Mn2+ quantum dots was dispersed in a solution of poly(vinyl alcohol) (PVA), de-ionized water, and alcohol to achieve a stable ink formulation. The ZnS:Mn2+ quantum dots exhibited both blue trap-state emission at around 430 nm and a strong orangered emission at about 600 nm with an excitation wavelength of 325 nm. The structural and optical properties of the ZnS:Mn2+ quantum dots were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Visible absorption spectrum and photoluminescence (PL) spectroscopy. XRD analysis showed the formation of cubic ZnS:Mn2+ particles with average sizes from 2.0 to 2.53 nm while the particle size was estimated to be 10 nm from transmission electron microscopy (TEM). The ZnS:Mn2+ quantum dots ink was printed on photographic paper using screen technique. The studied result indicated that the ZnS:Mn2+ quantum dots can be used in the ink printing of security documents and labels, light - emitting diodes (LEDs), in novel photoluminescent display and advertising.