Single Nanocrystal Spectroscopy and Pinned Emission of White Light-Emitting Cadmium Selenide Nanocrystals

Abstract

This project involves the characterization of ultrasmall white light-emitting CdSe nanocrystals and the development of new synthetic techniques for magic-sized CdSe and CdTe nanocrystals. The nature of the broad emission spectrum of white light-emitting CdSe nanocrystals was studied by ensemble and single nanocrystal fluorescence spectroscopy. Ensemble measurements determined that the shortest wavelength peak of the broad emission spectrum is independent of nanocrystal diameter below 1.7 nm. Ligand exchanges resulted in the degradation of the white-light emission spectrum, indicating that the white light-emission is heavily controlled by the nanocrystal surface. Single nanocrystal fluorescence spectroscopy measurements determined that the white light-emission originates from an individual nanocrystal and is not an ensemble effect. When the surface passivating ligand is changed from an alkylphosphonic acid to diisooctylphosphinic acid, quantized growth of CdSe nanocrystals is observed. Quantized growth is the hallmark of magic-sized nanocrystals, and the use of diisooctylphosphinic acid results in larger magic-sizes of CdSe and CdTe nanocrystals than previously observed.