Security printing of covert quick response codes using upconverting nanoparticle inks

Abstract

Counterfeiting costs governments and private industries billions of dollars annually due to loss of value in currency and other printed items. This research involves using lanthanide doped β-NaYF(4) nanoparticles for security printing applications. Inks comprised of Yb(3+)/Er(3+) and Yb(3+)/Tm(3+) doped β-NaYF(4) nanoparticles with oleic acid as the capping agent in toluene and methyl benzoate with poly(methyl methacrylate) (PMMA) as the binding agent were used to print quick response (QR) codes. The QR codes were made using an AutoCAD file and printed with Optomec direct-write aerosol jetting(®). The printed QR codes are invisible under ambient lighting conditions, but are readable using a near-IR laser, and were successfully scanned using a smart phone. This research demonstrates that QR codes, which have been used primarily for information sharing applications, can also be used for security purposes. Higher levels of security were achieved by printing both green and blue upconverting inks, based on combinations of Er(3+)/Yb(3+) and Tm(3+)/Yb(3+), respectively, in a single QR code. The near-infrared (NIR)-to-visible upconversion luminescence properties of the two-ink QR codes were analyzed, including the influence of NIR excitation power density on perceived color, in term of the CIE 1931 chromaticity index. It was also shown that this security ink can be optimized for line width, thickness and stability on different substrates.

Highly luminescent dual mode rare-earth nanorod assisted multi-stage excitable security ink for anti-counterfeiting applications

“…4,5 Only a single stage coding capability has been achieved so far by using these luminescent materials. This implies that the luminescent uorophores developed can be excited by a single wavelength, which subsequently emits only at a single wavelength.…”

Multilevel Data Encryption Using Thermal‐Treatment Controlled Room Temperature Phosphorescence of Carbon Dot/Polyvinylalcohol Composites

“…Optical data encryption plays an important role in applications such as document security,1 data storage,2 and anti‐counterfeiting 3. Conventional fluorescent color coding is limited by background interference which demands tedious decryption to extract the coded information 4.…”

Upconversion Nanoparticles for Other Applications

“…The printing time required using the Sono-Tek system, however, is much shorter than that for M 3 D. To print identical arrays of shapes and letters as presented here, screen printing with the Sono-Tek system deposited a single layer *9 times faster than M 3 D [64]. Kellar et al [65] also presented a work on security printing using UCNP ink. The details were similar with Luu's paper, and his highlight is that his UCNP ink contains both Yb 3+ /Er 3+ and Yb 3+ /Tm 3+ doped-NaYF 4 nanocrystals.…”