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apparently facilitated Mn 2+ incorporation by supplying preformed Mn—Sebonds, EPR spectra following surface exchange with pyridine were structureless(Fig. 24a and 24b). Further, in the case of Cd(Mn)Se, chemical etchingexperiments were conducted to remove surface layers of the NQDs and, withthem, any dopant that resided in these outer lattice layers. Etching revealedthat the distribution of Mn in the CdSe was not random. Most Mn 2+ dopantions resided in the near-surface layers, and only a small fraction resided nearthe core. These results are suggestive of a ‘‘zone-refining’’ process [64] andconsistent with the previously discussed tendency of NQDs to exclude defects.In the case of Zn(Mn)S DMSs, EPR and MCD experiments demonstratedthat the majority of Mn 2+ dopant resided well inside the NQD in highsymmetry,cubic Zn lattice sites. The dominant EPR signal comprised six-linespectra that exhibited hyperfine splitting of 60.4 10 4 cm 1 , similar to thesplitting observed for Mn in bulk ZnSe (61.7 10 4 cm 1 ) [66]. Also, thepresence of giant spin sublevel splitting at zero applied field, as demonstratedby MCD, provided additional evidence that the Mn 2+ dopant resided insidethe NQD. The dopant-induced sublevel splitting occurs only when there iswave function overlap between the dopant and the confined electron–holepair (i.e., only when Mn 2+ resides inside the NQD) [65,66].Sufficient experimental work has been conducted to begin to make a fewgeneral statements regarding solution-based preparation of DMS NQDs andthe synthetic parameters that most strongly influence the success of thedoping process. First, dopant ions can be excluded from the interior of theNQD to near-surface lattice sites when high-temperature nucleation andgrowth is employed [64] and/or limited (apparently) to approximately lessthan or equal to one dopant ion per NQD under such high-temperatureconditions [64,66]. Lower-temperature approaches appear to provide higherdoping levels. For example, a ‘‘moderate-temperature’’ organometallic-precursorapproach was recently used to successfully internally dope CdS withMn at very high levels: 2–12% as indicated by changes in x-ray diffractionpatterns with increasing Mn concentrations (Fig. 25) (EPR hyperfine structureconsistent with high-symmetry coordination of the dopant cations wasmost convincing for dopant concentrations V4%; Fig. 26 [42]). Exclusionfrom the lattice was only observed at dopant levels >15%. Single-sourceprecursors were used for both core and dopant ions [Cd(S 2 CNEt 2 ) 2 andMn(S 2 CNEt 2 ) 2 , respectively], and the reaction temperature was 120jC. Theparticles were rather large and rod-shaped (Fig. 27). Significantly, if repeatedat 300jC, dopant levels were limited to