Ex-situ mixed HgTe NPLs and QDs. For comparison to in-situ NPL/QD heterostructures, we perform a control experiment by first separately synthesizing oleylamine passivated HgTe QDs with sizes that match the in-situ grown QDs (Figure ), and then mix a comparable concentration with 3 ML HgTe NPLs isolated immediately after cation exchange (further details in S3). Hereafter we will refer to this sample as mixed NPLs and QDs. While we are able to reproduce energy transfer by mixing QDs and NPLs, there is less quenching of the band edge emission (Figure , green trace) suggesting lower efficiencies of transfer. From TEM we observe in-situ grown QDs in contact with the surface of the NPLs that are not washed away during centrifugation, while the mixed QDs are easily removed using gentle centrifugation which recovers NPL band edge PL (Figure and Figure ). We predict that the in-situ grown quantum dots are epitaxially attached or in very close proximity to the NPLs in the heterostructure (Figure ) which affords it such high energy transfer efficiencies compared to separately synthesized QDs and NPLs which are likely not adsorbing to the NPL surfaces, and thus constitute an "ideal" solution. The in-situ NPL/QD heterostructure not only allows for slow controlled growth of a low concentration of high PLQY QDs, but also overcomes distance limitations of energy transfer systems when the donor and acceptor are synthesized separately.