Comment on 'Semiconductor nanocrystals: structure, properties, and band gap engineering' [Acc. Chem. Res. Vol 43 (2) pp 190, (2010)]

TL;DR

This paper critiques and clarifies the understanding of surface trap states in CdSe quantum dots, emphasizing the correct energetic positions of electron and hole traps and revisiting their role in emission mechanisms.

Contribution

It provides a detailed analysis of surface trap states in CdSe QDs, correcting misconceptions about their energetic locations and offering a clearer framework for understanding emission processes.

Findings

Electron traps are close to the conduction band.

Hole traps are close to the valence band.

Revised understanding of surface state roles in emission.

Abstract

Surface traps and associated emission in quantum dots (QDs) sought a lot of research attention because of the fundamental interests apart from their influence on the emission characteristics. In ref [Acc. Chem. Res. Vol 43 (2) pp 190, 2010] the hole traps (h-traps) are depicted close to the conduction band (CB) for CdSe QDs while discussing the emission mechanism. However, notably electron traps (e-traps) are close to CB and h-traps are supposedly close to the valance band, especially in anion rich CdSe QDs. Although such emission (so called deep-trap) is a well known phenomenon, the energetic locations of these traps and the associated discrepancy require further attention. Hence the distinction between e, h-traps and their energetic location within the band gap is addressed in a general context, which is essentially a revisit to the surface states. Finally this general description is put to the context of surface states of CdSe QDs.