To give an estimate for the ratio of donor to acceptor, we calculate the concentration of both the NPLs and QDs in the in-situ heterostructure in the Supporting Information (Section S2). Briefly, an upper bound on the NPL concentration can be estimated from their average size and amount of precursor used in synthesis, assuming a 100% reaction yield for all steps including cation exchange. We observe very little change in the absorption spectra of the NPLs after the HgTe QDs have grown and show photoluminescence (PL), indicating that the QD growth occurs at low concentrations relative to the NPLs. To estimate the QD concentration, we found the difference in absorption at the QD band edge between a fresh NPL sample (no QD growth) and an aged NPL sample with QD growth (Figure ). We then used the absorption cross section to give an estimate of the QD concentration and found < 5 QDs per NPL for all of the in-situ samples we collected (Table ).