Size-dependent orbital symmetry of hole ground states in CdS nanocrystals

TL;DR

This study investigates how the orbital symmetry of hole ground states in CdS nanocrystals varies with size, revealing a transition from allowed to forbidden transitions and an anti-crossing phenomenon at a critical size.

Contribution

It provides experimental evidence for size-dependent orbital hierarchy and symmetry changes in CdS nanocrystals, confirming theoretical predictions.

Findings

Transition from orbital allowed to forbidden with decreasing size

Anti-crossing of s- and p-orbital hole levels at ~2 nm radius

Significant changes in radiative transition rates near critical size

Abstract

Using time-resolved photoluminescence spectroscopy, we studied the electronic levels of semiconductor nanocrystals (NCs) with small spin-orbit coupling such as CdS. Low temperature radiative rates indicate that the lowest energy transition changes from orbital allowed to orbital forbidden with decreasing NC size. Our results are well explained by a size-dependent hierarchy of s- and p-orbital hole levels that is in agreement with theoretical predictions. Around the critical NC radius of ~2 nm, we observe an anti-crossing of s- and p-orbital hole levels and large changes in transition rates.