Lead salts nanocrystal quantum dots (PbX QDs, X: S, Se, Te) with their photoluminescence (PL) emission tunable from the near to mid-infrared have been attractive for their potential applications in photovoltaic and biomedical imaging as well as classical and quantum light sources operating in telecommunication bands. The band-edge exciton fine structure of these PbX QDs are expected to be more complex than the well-studied II-VI and III-V QDs due to complex interplay between 64-fold degenerated band-edge excitons and effects such as electron-hole exchange and shapes asymmetry. Unraveling the mysteries of band-edge exciton fine-structure requires lifting the spin degeneracy and brightening the forbidden optical transitions via application of an external high magnetic field.<sup>[1,2]</sup> It is also necessary to conduct this magneto-PL spectroscopy at low temperature and at the level of individual QDs to completely eliminate thermal and ensemble (inhomogeneous) broadening of spectral features. Let alone conducting such a magneto-PL study, performing a relatively simple single dot low-temperature PL study remained a challenge for PbX QDs due to factors involving fast photodegradation and slow radiative decay rate of PbX QDs, as well as the high noise level of commonly used infrared detectors. Here we report a low-temperature polarization-resolved magneto-PL spectroscopy of individual colloidal PbS/CdS core/thick-shell QDs. We were able to measure the anisotropic exchange splitting arising from the shape asymmetry of the PbS cores as well as Zeeman splitting and g factor as a function of emission wavelength. This unprecedented study is enabled by PL bleaching-free PbS/CdS core/thick-shell QDs and ultra-low noise InGaAs detector operating at liquid nitrogen temperature.<br/><br/>

Low temperature, polarization resolved, magneto-photoluminescence spectroscopy of individual colloidal lead salt quantum dots

2019 Spring National Meeting

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