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CAREER: New Probes of Heterogeneity in Next-Generation Nanocrystal Emitters: University of California-Los Angeles

Justin Caram

[email protected]

Professor Justin R. Caram of the University of California-Los Angeles is supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program and the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program of the Division of Chemistry to develop new spectroscopic measurement methods to study the emission of short-wave infrared light from quantum dots. The quantum dots are incredibly small, man-made nanocrystals with diameters about 10,000 times narrower than a human hair. The research seeks to overcome the current limitations on instrumentation and methods at the single nanocrystal level. This goal is important because the nanocrystals come as an non-uniform mix of particles with different sizes, shapes and structures. This mixture complicates their study and hinders their use in optoelectronic devices. The knowledge obtained on single crystals may open the way for the systematic formation of uniform quantum dot materials with decreased toxicity and new functionality in the short-wave infrared — a spectral region beyond where human eyes can see. Success in conducting the research may widens the use of quantum dots in biomedical imaging, next-generation optoelectronic devices, optical communications, and solar energy conversion. During the course of this research, Professor Caram is revamping general chemistry courses through the development of learning laboratories that incorporate new pedagogical technologies to help students develop skills and motivation to continue their schooling in STEM majors after their first year in college. <br/> <br/>In this project, Professor Caram and his research team are supported to develop spectroscopic techniques to probe the intrinsic photo properties of short-wave infrared emitting (SWIR) colloidal nanocrystals, including HgX and CuInS2. The statistical variations from nanocrystal to nanocrystal and the average and distribution of exciton and mutilexciton lifetimes, yields and spectra of these nanoparticles in solution are assessed. SWIR photon-counting and correlation is achieved using recently developed spectroscopic tools. The project combines new infrared active detectors suitable for efficient photon counting, timing and correlation in shortwave infrared; path-length Mach-Zehnder interferometry to attain simultaneous temporal and spectral resolution, and fluorescence correlation spectroscopy to probe emitters as they diffuse through a focal volume in dilute solution. The research starts with a focus on HgX (X=S, Se, Te) quantum confined nanocrystals, which exhibit tunable bandgaps from 0 to 1.6 eV and have a wide range of applications in lasing, quantum communications, and infrared sensing. The focus shifts to the toxic cadmium-free nanostructure (CuInS2), which displays complex ensemble photoluminescence, including trap/defect emission, electrochemical doping and non-stoichiometry. The method employed resolves and correlates the energies of emitted photons as a function of inter-photon spacing, creating a two-dimensional map of emitter stream from dilute ensemble, in analogy to two-dimensional electronic spectroscopy.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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