Extended Data Fig. 2: Mn-doped PbSe/CdSe core/shell QDs.
From: Spin-exchange carrier multiplication in manganese-doped colloidal quantum dots
a, A schematic depiction of a Mn-doped PbSe/CdSe QD. b, An exemplary TEM image of a QD from one of the Mn-doped PbSe/CdSe QD samples (sample Mn-1). The PbSe core radius (r) is 2.3 nm, the CdSe shell thickness (h) is 1.6 nm, and the overall QD radius (R) is 3.9 nm. c, The absorption (top) and emission (bottom) spectra of the Mn-doped PbSe/CdSe QDs as a function of duration of a cation exchange reaction (tCE) leading to formation of the CdSe shell (red and orange traces). The spectra of the original undoped PbSe QDs are shown in black. The spectra of Mn-doped PbSe QDs before cation exchange are shown in green. After doping with Mn, the PL of the PbSe QDs is completely quenched. It is recovered after the formation of the CdSe shell. The progressive increase of the CdSe-shell thickness leads to the shrinkage of the PbSe core, which manifests as a blue shift of the PL spectrum and the band-edge absorption feature. Inset: Mn content as a function of tCE. d, Modeling of diffusion doping of PbSe QDs using Fick’s 2nd law of diffusion leads to a Mn distribution shown by the black line. The diffusion parameters are selected so as to yield the total content of Mn ions of 8% (defined by the area under the black trace), which corresponds to the experimental situation in the case of sample Mn-1. Then, we assume that during cation exchange, Cd2+ replaces the original cations within the shell region. The resulting distribution of Mn ions is given by the red trace. Based on the area under this trace, the Mn content is reduced to 2%, which is close to the experimental value of 1.6%. This analysis suggests that the distribution of the Mn ions is peaked at the core/shell interface and gradually decays towards the PbSe core centre.
