David M. Schut

Optically coded nanocrystal taggants and optical frequency IDs

A series of nanocrystal and nanocrystal quantum dot taggant technologies were developed for covertly tagging and tracking objects of interest. Homogeneous and heterogeneous nanocrystal taggant designs were developed and optimized for ultraviolet through infrared emissions, utilizing either Dexter energy transfer or Förster resonant energy transfer (FRET) between specific absorbing and emitting functionalities. The conversion efficiency, target-specific identification, and adhesion properties of the taggants were engineered by means of various surface ligand chemistries. The ability to engineer poly-functional ligands was shown effective in the detection of a biological agent simulant, detected through a NC photoluminescence that is altered in the presence of the agent of interest; the technique has broad potential applicability to chemical, biological, and explosive (CBE) agent detection. The NC photoluminescence can be detected by a remote LIDAR system; the performance of a taggant system has been modeled and subsequently verified in a series of controlled field tests. LIDAR detection of visible-emitting taggants was shown to exceed 2.8 km in calibrated field tests, and from these field data and calibrated laboratory measurements we predict >5 km range in the covert shortwavelength infrared (SWIR) spectral region.

Visible Discrimination of Broadband Infrared Light by Dye-Enhanced Upconversion in Lanthanide-Doped Nanocrystals

Optical upconversion of near infrared light to visible light is an attractive way to capture the optical energy or optical information contained in low-energy photons that is otherwise lost to the human eye or to certain photodetectors and solar cells. Until the recent application of broadband absorbing optical antennas, upconversion efficiency in lanthanide-doped nanocrystals was limited by the weak, narrow atomic absorption of a handful of sensitizer elements. In this work, we extend the role of the optical antenna to provide false-color, visible discrimination between bands of infrared radiation. By pairing different optical antenna dyes to specific nanoparticle compositions, unique visible emission is associated with different bands of infrared excitation. In one material set, the peak emission was increased 10-fold, and the width of the spectral response was increased more than 10-fold.

Solution processible nanoparticle thermoelectric materials

The fabrication of stoichiometric (BixSb1- x)2Te3 thermoelectric films comprised of nanostructured building blocks were fabricated using solution processing compatible methods. Nanostructured films of n-type Bi2Te3, (Bi0.75Sb0.25)2Te3, and (Bi0.50Sb0.50)2Te3 and p-type (Bi0.25Sb0.75)2Te3 and Sb2Te3 TE thermoelectric materials were fabricated using intercalated and exfoliated stoichiometric bulk materials. Fine control was exerted over the composition and reaction to maintain the purity and effectiveness of the nanostructured alloys composition of the materials as they were deposited, pressed, and annealed in a Te-rich ambient. A Seebeck coefficient was measured to be -235 μVK-1 for the n-type Bi2Te3 films, and 262 μVK-1 for the p-type (Bi0.25S0.75)2Te3 films. Although limited by high resistance, due to cracking of the films, ZT was estimated to be between 0.8 and 1.69 for the n-type films and an order of magnitude lower for the p-type films.