Shape dependence of band-edge exciton fine structure in CdSe nanocrystals

Nano Lett. 2007 Nov;7(11):3274-80. doi: 10.1021/nl0713070. Epub 2007 Sep 27.

Abstract

The band-edge exciton fine structure of wurtzite CdSe nanocrystals is investigated by a plane-wave pseudopotential method that includes spin-orbit coupling, screened electron-hole Coulomb interactions, and exchange interactions. Large-scale, systematic simulations have been carried out on quantum dots, nanorods, nanowires, and nanodisks. The size and shape dependence of the exciton fine structure is explored over the whole diameter-length configuration space and is explained by the interplay of quantum confinement, intrinsic crystal-field splitting, and electron-hole exchange interactions. Our results show that the band-edge exciton fine structure of CdSe nanocrystals is determined by the origin of their valence-band single-particle wave functions. Nanocrystals where the valence-band maximum originates from the bulk A band have a "dark" ground-state exciton. Nanocrystals where the valence-band maximum is derived from the bulk B band have a "quasi-bright" ground-state exciton. Thus, the diameter-length configuration map can be divided into two regions, corresponding to dark and quasi-bright ground-state excitons. We find that the dark/quasi-bright ground-state exciton crossover is not only diameter-dependent but also length-dependent, and it is characterized by a curve in the two-parameter space of diameter and length.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cadmium Compounds / chemistry*
  • Computer Simulation
  • Crystallization
  • Electrons
  • Molecular Conformation
  • Nanoparticles / chemistry
  • Nanotechnology / methods*
  • Particle Size
  • Quantum Dots
  • Quantum Theory
  • Selenium Compounds / chemistry*

Substances

  • Cadmium Compounds
  • Selenium Compounds
  • cadmium selenide