Role of Valley Anisotropy in Optical Absorption of Monodisperse PbS Nanocrystals

Abstract

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.

Exciton Fine Structure in Lead Chalcogenide Quantum Dots: Valley Mixing and Crucial Role of Intervalley Electron–Hole Exchange

“…To overcome this problem, in ref 9 the bulk electron energy dispersion 15 and the experimental effective masses 16 were used to obtain the tight-binding (TB) parameters of PbS and PbSe suitable for large-scale calculations. 6,17 Note that, in practical realizations of the TB method, surface passivation is not required due to the high ionicity of PbX. 9,11,18 For our TB calculations we model QDs as truncated cubes "carved out" from the bulk rocksalt lattice by the {100} and {111} planes separated by the distances of a 0 (N + 1/2) and − a N M…”

“…However, due to computational complexity these approaches can be hardly applied to the systematic calculations of the nanostructures. To overcome this problem, in ref the bulk electron energy dispersion and the experimental effective masses were used to obtain the tight-binding (TB) parameters of PbS and PbSe suitable for large-scale calculations. , Note that, in practical realizations of the TB method, surface passivation is not required due to the high ionicity of PbX. ,, …”

Intrinsic Exciton Photophysics of PbS Quantum Dots Revealed by Low-Temperature Single Nanocrystal Spectroscopy

“…Here we use notations for the irreducible representations of the point symmetry group T d consistent with those of ref . The oscillator strengths of optical transitions that distribute nonuniformly among the eight triplets are determined by numerical calculations in the framework of the empirical tight-binding model. , First, the electron and hole states are calculated using the nearest-neighbor sp 3 d 5 s* tight-binding approach with the parameters accurately fitted to reproduce ab initio many-body calculations of PbS band structure . We neglect the passivation of the surface, which only slightly changes the quantum confinement energies of the states near the band gap.…”

Shape effect on the valley splitting in lead selenide nanowires

“…Among many atomistic methods we chose the empirical tight binding approach in nearest neighbour approximation, proved to be useful for many cubic semiconductors [30]. The use of the recent parametrization [26], which accurately reproduces experimental effective masses in the L valleys and show good agreement with experiment [31], allow us to study a wide range of NW sizes and shapes. We neglect the surface passivation, as the surface states in highly ionic crystals lie far outside the band gap [22] and there is no need to saturate the dangling bonds [25].…”