Anisotropy-induced optical transitions in PbSe and PbS spherical quantum dots

Optical-absorption spectra of PbSe and PbS spherical quantum dots have been studied both theoretically and experimentally. Exact theoretical analysis of the energy spectra and optical transitions has been carried out in the framework of four-band $\mathbf{k}\cdot \mathbf{p}$-method with full account of the anisotropy effects. It is demonstrated that strong anisotropy of the energy bands of bulk PbSe and PbS results in pronounced optical transitions in quantum dots, which are forbidden in isotropic approximation. These anisotropy-induced transitions have been clearly observed in the measured absorption spectra of the PbSe and PbS quantum dots.