posted on 2021-09-21, 15:45authored byChenghui Xia, Philippe Tamarat, Lei Hou, Serena Busatto, Johannes D. Meeldijk, Celso de Mello Donega, Brahim Lounis
Semiconductor
copper indium sulfide quantum dots are emerging as
promising alternatives to cadmium- and lead-based chalcogenides in
solar cells, luminescent solar concentrators, and deep-tissue bioimaging
due to their inherently lower toxicity and outstanding photoluminescence
properties. However, the nature of their emission pathways remains
a subject of debate. Using low-temperature single quantum dot spectroscopy
on core–shell copper indium sulfide nanocrystals, we observe
two subpopulations of particles with distinct spectral features. The
first class shows sharp resolution-limited emission lines that are
attributed to zero-phonon recombination lines of a long-lived band-edge
exciton. Such emission results from the perfect passivation of the
copper indium sulfide core by the zinc sulfide shell and points to
an inversion in the band-edge hole levels. The second class exhibits
ultrabroad spectra regardless of the temperature, which is a signature
of the extrinsic self-trapping of the hole assisted by defects in
imperfectly passivated quantum dots.