We
study light absorption by nearly monodisperse PbS nanocrystals
grown in a glass matrix. The absorption spectra demonstrate a well-resolved
structure at energies above the first absorption peak. The absorption
cross sections are calculated with an empirical tight-binding model
accounting for the quantum confinement, the band anisotropy, and valley
splittings. Absorption spectra measured at 4 K quantitatively agree
with the atomistic calculations. This allows us to unambiguously ascribe
the much-debated second absorption peak to the p–p optical
transition and directly measure the splitting of excited p states.
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