Optical investigation of quantum confinement in PbSe nanocrystals at different points in the Brillouin zone

R. Koole, G. Allan, C. Delerue, A. Meijerink, D.A.M. Vanmaekelbergh, A.J. Houtepen

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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 ED-1.5 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 -point in the Brillouin zone. Tight-binding calculations confirm that the high-energy transitions originate from the -point in the Brillouin zone. The -character of the high-energy transitions may be of importance to explain the mechanism behind multiple exciton generation in PbSe nanocrystals.
Original languageUndefined/Unknown
Pages (from-to)127-133
Number of pages7
JournalSmall: nano micro
Issue number1
Publication statusPublished - 2008

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