Band-edge exciton states in bulk lead chalcogenides are 64-fold degenerate. In quantum dots (QDs), the degeneracy is lifted by the valley mixing and the electron-hole exchange interaction. To investigate their interplay we calculate excitonic states in PbS QDs within the tight-binding method. This allows one to trace the genesis of the bright excitonic states from the valley-degenerate states of the direct exciton which may be described within the effective mass model. We compute optical absorption spectra fully accounting for the exciton fine structure within the tight-binding method and extend the effective-mass model to include description of the inter-valley coupling.
Dephasing of optical excitations in semiconductor quantum dots (QDs) has recently received much attention. A common model used for understanding such processes is a two-level electronic system interacting with phonons. In our work we construct a consistent non-perturbative theory of the ZPL homogeneous broadening and resolve the contradictions by pointing out the limits of validity of the theoretical papers mentioned.
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