Resonance Raman polarization and high-energy excitonic states in semiconductor nanocrystals

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With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program in the Division of Chemistry, Professors Anne Kelley and David Kelley of the University of California, Merced are exploring how the size, shape, and composition of semiconductor nanocrystals (NCs) influence their interactions with light. When the size of a semiconductor particle is just a few nanometers, or about a million times smaller than the period at the end of this sentence, it interacts with light in unique ways that depend on the nanoparticle's size and shape. Usually, NCs are assumed to be perfect spheres or cylinders with smooth surfaces, but in actuality this is not the case. Professors Kelley and Kelley and their research group will synthesize NCs with a variety of shapes and compositions to explore how shape and surface imperfections affect the excited states created by light absorption. Their discoveries could lead to improved materials for displays such as optical light-emitting diodes (OLEDs), artificial lighting, and biomedical imaging. This project will contribute to the education and training for graduate students and postdoctoral scholars and provide research opportunities for undergraduate students from diverse backgrounds.The proposed research will use the polarization of resonance Raman (RR) scattering and photoluminescence to examine the symmetries of the excitons in II-VI semiconductor NCs, particularly the higher-energy excitons that are difficult to access by other techniques. The focus will be on pure CdSe and core/shell NCs for which synthetic routes to producing high-quality materials are well developed and where the extent of shape anisotropy can be varied systematically. Spectroscopy and spectroscopic simulations will be performed on NCs of different shapes (quantum dots, cubes, nanoplatelets, nanorods, and dot-in-rods) and as a function of size, surface ligands, and annealing of core/shell interfaces. The project will exploit the polarization properties of RR scattering to probe the local environment of the excitonic states at different excitonic energies and at interior versus surface or interface regions.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.