Carnegie Mellon

Due to small, “sub-excitonic” dimensions, semiconductor nanocrystals can produce novel electronic interactions that involve charges residing in intrinsic quantized states as well as species located at nanocrystal surfaces. Strong interactions between quantum-confined carriers open, for example, a new nanocrystal-speci fic energy relaxation channel associated with Augertype electron-hole energy transfer [1]. These interactions are also responsible for highly efficient nonradiative Auger recombination [2], which represents the main obstacle to applications of nanocrystals in practical lasing technologies [3]. Strong interactions between conductionand valence-band electrons can lead to an interesting regime of photogeneration of multiple electronhole pairs by single photons known as carrier multiplication [4]. Finally, direct coupling of nanocrystal excitations to surface species can allow for ultrafast extraction of “hot” carriers prior to their relaxation to the band-edge states [5]. The processes of carrier multiplication and hotelectron extraction have attracted signi ficant recent interest due to their potential applications in generation-III solar energy conversion technologies.