Optical absorption and emission of α-Sn nanocrystals from first principles

Abstract

We investigate the optical properties of hydrogenated α-Sn nanocrystals up to diameters of 3.6 nm in the framework of an ab initio pseudopotential method including spin-orbit interaction (SOI) and the repeated supercell approximation. The fundamental absorption and emission edges are determined including quasiparticle effects and electron-hole interaction. The atomic geometries in the ground and excited electronic states follow from total energy optimization. We discuss the oscillator strengths of the optical absorption near the fundamental gaps for the most important transitions. We demonstrate that the spectra can only be correctly described including SOI. The strongly size-dependent Stokes shifts between optical absorption and emission are shown to be mainly a consequence of the different atomic geometries.

Electronic, Structural, and Vibrational Properties of α-Sn Nanocrystals Built From Diamondoid Structures: Ab Initio Study

“…Since we are dealing with cages and not spheres the resultant HOMO and LUMO energies might slightly violate the quantum confinement reduction of the gap due to shape effects. The comparison of the present calculated gap with that of [2] manifests the accuracy of the present method. The calculated gap of [2] is in an entirely different pseudopotential method and an entirely different number of Sn atoms that do not have diamondoids structure.…”

“…The comparison of the present calculated gap with that of [2] manifests the accuracy of the present method. The calculated gap of [2] is in an entirely different pseudopotential method and an entirely different number of Sn atoms that do not have diamondoids structure. The slightly higher gap of the present diamondoids is an indicator of the tighter structure [13].…”

“…Twodimensional (2-D) nano films of cubic α-Sn are found to be a topological semimetal [2], [3]. Methods that are used to simulate nanoscale Sn particles span the already known pseudopotential and k.p methods with different structures [2], [4]. In this paper we shall divert from these methods by constructing Sn nanoparticles similar to the already found experimentally for carbon and silicon i.e., diamondoids [5].…”

“…At the nanoscale, cubic α-Sn indirect gap turns to be direct with the gap having a finite value depending on the size of the nanoparticle [1]. Twodimensional (2-D) nano films of cubic α-Sn are found to be a topological semimetal [2], [3]. Methods that are used to simulate nanoscale Sn particles span the already known pseudopotential and k.p methods with different structures [2], [4].…”

Unfolding the band structure of disordered solids: From bound states to high-mobility Kane fermions

“…GaBi is a metal with an anomalous order of bands [41], which is reminiscent of the better known α-Sn with a band inversion or negative band gap caused by spin-orbit effects [42]. Thus, the electronic structures of GaAs and GaBi have different topology, which is not the case in GaAs-GaSb, for instance.…”