Polarised Photoluminescence from Surface-Passivated PbS Nanocrystals

TL;DR

This study demonstrates that surface-passivated PbS nanocrystals exhibit two distinct, strongly polarized photoluminescence components with different excitation dependencies and temporal behaviors, revealing two types of passivated nanocrystals.

Contribution

It uncovers the polarization characteristics and temporal dynamics of photoluminescence in surface-passivated PbS nanocrystals, identifying two distinct nanocrystal types.

Findings

Both emission components are strongly polarized.

Band-edge polarization is excitation-independent.

Above-band-edge polarization is excitation-dependent and short-lived.

Abstract

Effective surface-passivation of PbS nanocrystals in aqueous colloidal solution has been achieved following treatment with CdS precursors. The resultant photoluminescent emission displays two distinct components, one originating from the absorption band-edge and the other from above the absorption band-edge. We show that both of these components are strongly polarised but display distinctly different behaviours. The polarisation arising from the band-edge shows little dependence on the excitation energy while the polarisation of the above-band-edge component is strongly dependent on the excitation energy. In addition, time resolved polarisation spectroscopy reveals that the above-band-edge polarisation is restricted to the first couple of nanoseconds, while the band-edge polarisation is nearly constant over hundreds of nanoseconds. We recognise an incompatibility between the two different polarisation behaviours, which enables us to identify two distinct types of surface-passivated PbS nanocrystal.