Patterned direct-write and screen-printing of NIR-to-visible upconverting inks for security applications

Abstract

Two methods of direct-write printing for producing highly resolved features of a polymer impregnated with luminescent upconversion phosphors for security applications are presented. The printed polymer structures range in shape from features to text. The thin polymer features were deposited by direct-write printing of atomized material as well as by screen-printing techniques. These films contain highly luminescent lanthanide-doped, rare-earth nanocrystals, β-NaYF₄:3%Er, 17%Yb, which are capped with oleic acid. This capping agent allows the nanocrystals to disperse throughout the films for full detailing of printed features. Upconversion of deposited features was obtained using a 980 nm wavelength laser with emission of upconverted light in the visible region at both 540 and 660 nm. Features were deposited onto high bond paper, Kapton®, and glass to demonstrate possible covert and forensic security printing applications, as they are printed in various features and invisible to 'naked-eye' viewing at low concentrations of nanocrystals.

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).…”

“…To simplify the operating process, Blumenthal et al developed a one-step printing process accompanied by Sono-Tek screen-printing and M3D direct-write printing process based on NIR-to-visible inks composed of β-NaYF4:Yb 3+ , Er 3+ nanoparticles in a polymer matrix 12 . In addition, poly (methyl methacrylate) (PMMA) is used as inks binding reagent to maintain film uniformity in these printing systems 12,16 . Although significant progress has been made, there are several limitations associated with these existing printing platforms.…”

Upconversion Nanoparticles for Other Applications

“…With M 3 D, however, essentially all of the deposited material contributes to the desired print feature. 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.…”

“…In 2012, Luu et al [64] developed a composite ink that was compatible with two separate printing systems (direct-write printing and aerosol jet printing), for producing highly resolved printed features which are invisible under ambient light, but produce luminescent images visible by the naked eye upon 980-nm excitation. The synthesis, printing, and imaging processes are as following:…”

Ultrasmall lanthanide-doped nanoparticles as multimodal platforms

“…In particular, there has been intense interest in applying these materials to solar energy harvesting [1][2][3][4][5], display lighting [6][7][8][9][10], security inks [11][12][13][14] , photocatalysis [15] , and biomedical imaging [16][17][18][19][20][21] . In particular, rareearth doped nanoparticles are especially useful for biomedical applications because of their sharp absorption and emission lines in the visible and near-infrared (NIR).…”