Optical Investigation of Quantum Confinement in PbSe Nanocrystals at Different Points in the Brillouin Zone

Abstract

We present detailed investigations on the optical properties of PbSe nanocrystals. The absorption spectra of monodisperse, quasispherical nanocrystals exhibit sharp features as a result of distinct optical transitions. To study the size dependence, absorption spectra of nanocrystals ranging from 3.4 to 10.9 nm in diameter are analysed and a total of 11 distinct optical transitions are identified. The assignment of the various optical transitions is discussed and compared to theoretically calculated transition energies. By plotting all transitions as a function of nanocrystal size (D) we find that the energy (E) changes with the following relationship E / D À1.5 for the lowest energy transitions. The transition energy extrapolates to approximately 0.3 eV for infinite crystal size, in agreement with the bandgap of bulk PbSe at the L-point in the Brillouin zone. In addition, high-energy transitions are observed, which extrapolate to 1.6 eV for infinite crystal size, which is in good agreement with the bulk bandgap of PbSe at the S-point in the Brillouin zone. Tight-binding calculations confirm that the high-energy transitions originate from the S-point in the Brillouin zone. The S-character of the high-energy transitions may be of importance to explain the mechanism behind multiple exciton generation in PbSe nanocrystals.

Analysis of Particle Size Distributions of Quantum Dots: From Theory to Application

“…and Smith D.W., 1994;Cademartiri L. et al, 2006;Kane R.S. et al, 1996;Moreels I. et al, 2009) and b) PbSe (Dai Q. et al, 2009;Koole R. et al, 2008;Lipovskii A. et al, 1997;Liu Y. et al, 2010;Ma W. et al, 2011;Moreels I. et al, 2007;Pietryga J.M. et al, 2004;Sashchiuk A. et al, 2001;Steckel J.S.…”

Effect of symmetry breaking on the optical absorption of semiconductor nanoparticles

“…The T d group, one of the highest symmetry among the 3D crystallographic point groups, leads to a large number of selection rules with many dipole transitions forbidden to first order. Thus, in highly symmetric NPs, crystal momentum selection rules may not be relaxed sufficiently, particularly for larger sizes 28 . Reducing the symmetry of the NPs can lift more selection rules for dipole transitions, opening new channels for photon absorption.…”

Multiple Exciton Generation in Nanostructures for Advanced Photovoltaic Cells

“…e peaks in transition absorption observed in the experiment may be associated with speci c, previously known orbital energies [43]. In particular, the socalled ∑ transitions to the "Brillouin Zone" (unique to PbSe), a set of electronic transitions where MEG is expected to be particularly strong due to an enhanced phonon bottleneck, were investigated by probing the biexciton dynamics through transient absorption.…”