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.

In this study silver nanoparticles were synthesized with short chain (C6-C10) carboxylic acids as capping agents and prepared as conductive inks for fabricating electrically conductive patterns using direct write technologies. The structural characterization of as-synthesized nanoparticles revealed that the particles are spherical in shape with narrow size distribution (4.1 to 4.7 nm) and have face centered cubic crystal structure. Silver-particle-based inks were prepared by dispersing the particles in toluene and separating non-dispersing particles from the inks. The loading of silver particles in the solvent was increased with the increasing chain length of capping agents. As a result, inks with a wide range of nanoparticulate concentrations ($3 to 66 wt%) were able to be prepared and most of these inks were stable for at least a month. All the inks exhibited shear thinning behavior and this shear thinning became more prominent for higher concentration inks. As the nanoparticle concentration of the inks was increased, surface tension was decreased and the contact angles of the inks with the KaptonÒ and glass were increased. Printing of microelectrodes, lines and films was carried out using aerosol jet printing and ultrasonic spray coating. The conductivity of printed microelectrodes was 10 to 87% of the bulk silver conductivity with the sintering temperatures as low as 130 to 250 C depending on the ink used.

Perovskite thin films are thermally annealed using a rapid intense pulsed light technique enabled by an alkyl halide that collectively improves device performance when processed in ambient conditions.