Structure of excited-state transitions of individual semiconductor nanocrystals probed by photoluminescence excitation spectroscopy

Phys Rev Lett. 2004 Oct 29;93(18):187402. doi: 10.1103/PhysRevLett.93.187402. Epub 2004 Oct 28.

Abstract

We perform for the first time photoluminescence excitation (PLE) studies of individual nanocrystals (NCs) that reveal the structure of excited-state transitions not obscured by ensemble averaging. Single-NC PLE spectra strongly deviate from a traditional idealized picture of sharp, quasiatomic resonances. We detect only a few relatively narrow transitions (3-4 meV) at the band edge, while at higher spectral energies, we observe a broad structureless feature separated from the band-edge peaks by a >50 meV "minigap." These observations can be rationalized by analyzing hole intraband relaxation behavior.