The influence of quantum confinement on the one- and two-photon absorption spectra (1PA and 2PA) of PbS and PbSe semiconductor quantum dots (QDs) is investigated. The results show 2PA peaks at energies where only 1PA transitions are predicted and 1PA peaks where only 2PA transitions are predicted by the often used isotropic k•p four-band envelope function formalism. The first experimentally identified two-photon absorption peak coincides with the energy of the first one photon allowed transition. This first two-photon peak cannot be explained by band anisotropy, verifying that the inversion symmetry of the wave functions is broken and relaxation of the parity selection rules has to be taken into account to explain optical transitions in lead-salt QDs. Thus, while the band anisotropy of the bulk semiconductor plays a role in the absorption spectra, especially for the more anisotropic PbSe QDs, a complete model of the absorption spectra, for both 1PA and 2PA, must also include symmetry breaking of the quantum confined wave functions. These studies clarify the controversy of the origin of spectral features in lead-salt QDs. © 2010 American Chemical Society.
|Original language||English (US)|
|Number of pages||6|
|State||Published - Sep 8 2010|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-I1-009-21
Acknowledgements: This material is based upon work supported in part by the U.S. Army Research Office under Contract/Grant 50372-CH-MUR, the Air Force Office of Sponsored Research MURI AFOSR Grant FA9550-06-1-0337, the DARPA ZOE program Grant W31R4Q-09-1-0012, and the Israel Ministry of Defense contract 993/54250-01 and by Award No. KUS-I1-009-21, made by King Abdullah University of Science and Technology (KAUST). We also would like to thank Frank W. Wise for helpful discussions.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.