Photoluminescence from single semiconductor nanostructures

We review some recent results in the spectroscopy of single CdSe nanocrysta l quantum dots. By eliminating the effects of inhomogeneous broadening and ensemble averaging, single nanocrystal spectroscopy has revealed many new a nd previously unexpected physical phenomena. Among those discussed in this review are ultra-narrow emission lineshapes (similar to 600x narrower than ensemble spectra), a highly polarizable emitting state in the presence of s trong local electric fields, line broadening as a result of environmental f luctuations, and shifting of the emission spectra over a wide range of ener gies (from less than 300 mu eV to 80 meV). In addition, polarization spectr oscopy of single nanocrystals has revealed the presence of a theoretically predicted two-dimensional transition dipole moment oriented in the xy plane of the nanocrystals. As a result, it is, in principle, possible to use pol arization spectroscopy to determine the three-dimensional orientation of in dividual nanocrystals. These and other studies of single quantum dots have provided us with significant insight into the detailed physics and dynamics of this unique and fascinating physical system.