Rare-Earth Doped Nanoparticles in Security Printing Applications

Abstract

In this work, lanthanide-doped, sodium yttrium fluoride nanocrystals were prepared and dispersed in a solvent consisting of 90 vol% toluene and 10 vol% methyl benzoate. Poly (methyl methacrylate) polymer was dissolved in the solvent, in addition to the nanocrystals. Inks were printed using direct-write techniques. Substrates used included Kapton®, bond paper, metal and glass. Stencil patterns and QR codes were printed with these inks. An overview of direct write printing for security applications is given. On many substrates, these printed traces are difficult to detect in ambient lighting, but can be easily read using near-infrared (NIR) illumination, making them very useful for covert and semi-covert security printing applications.

Inkjet printing of upconversion nanoparticles for anti-counterfeit applications

“…Solvent based ink was prepared with cyclohexane ( equals to 0.886 mpa.s and equals to 24.4 mN/m, 25 ℃), which was used to disperse UCNPs, and glycerol trioleate ( equals to 37.8 mpa.s and equals to 34.7 mN/m, 25 ℃), which was suitable for preparing a mixture with moderate viscosity and surface tension. Compared to previous reported methods [12][13][14]16 , both the ink components and the preparation procedures are easier for operation and mass production. 3a-b).…”

“…3c, d). Compared to previous reported methods, [12][13][14]16 both the ink components and the preparation procedures are easier for operation and mass production. This demonstrates the advantage in using the inkjet printer by applying UCNPs for high-throughput security printing.…”

“…Compared with screen printing 12,13 and aerosol jet printer 12,15,16 , the developed inkjet printing provides higher spatial resolution of smaller than 200 μm (Fig 4d). Furthermore, the HP Deskjet 1000 printer applied in this study has its black-and-white DPI of 600×600.…”

“…Compared with screen printing 12,13 and aerosol jet printer, 12,15,16 the developed inkjet printing provides higher spatial resolution of less than 200 μm (Fig. 4d).…”

“…In contrast, near-infrared (NIR)-to-visible luminescent materials based on the so-called 'upconversion' luminescence are more difficult to duplicate as compared with UV-to-visible materials. [11][12][13][14][15][16][17] Besides, the NIR excitation sources are more difficult to access and will not excite standard downconversion luminescent materials, making it possible to print patterns on highly fluorescent surfaces (e.g., papers and textiles with optical brighteners). 18 Moreover, upconversion materials can be formulated to produce the designed emission color only at specific excitation power densities 19 and the designed luminescence lifetime by controlling the ratio of Yb and Tm, 20,21 making it even more difficult to duplicate.…”