Luminescent Ink Based on Upconversion of NaYF4:Er,Yb@MA Nanoparticles: Environmental Friendly Synthesis and Structural and Spectroscopic Assessment

NaYF4:Er,Yb upconversion luminescent nanoparticles (UCNPs) were prepared by hydrothermalmethods at 180 C for 24 h. The X-ray diffraction (XRD) and TEM (transmission electronmicroscopy) images show that the resulting 60 nm UCNPs possess a hexagonal structure. In thiswork, maleic anhydride (MA) was grafted on the surface of UCNPs to induce hydrophilic properties.The photoluminescence spectra (PL) show upconversion emissions centered around 545 nm and660 nm under excitation at 980 nm. The luminescent inks, including UCNPs@MA, polyvinyl alcohol(PVA), deionized water (DI), and ethylene glycol (EG), exhibit suitable properties for screen printing,such as high stability, emission intensity, and tunable dynamic viscosity. The printed patterns with aheight of 5 mm and a width of 1.5 mm were clearly observed under the irradiation of a 980 nm laser.Our strategy provides a new route for the controlled synthesis of hydrophilic UCNPs, and showsthat the UCNPs@MAs have great potential in applications of anti-counterfeiting packing