Anion Exchange in Discretely Grown Semiconductor Nanomaterials

Ion exchange is emerging as a powerful post-synthetic strategy to engineer unprecedentedly high-quality nanomaterials by tuning chemical composition, crystal phase, doping, and morphology. Several heterostructured nanocrystals have been prepared through cation exchange (CE) reactions. However, in contrast to CE, the study of anion exchange (AE) processes is still in its infancy. Since the larger size and slower migration rate of anions, the exchange process usually requires high reaction temperatures, which leads to the reconstruction of the original frameworks, thus causing structural changes or collapse. Here, we used magic size clusters (MSCs) and nanoplatelets (NPLs), two discretely grown nanomaterials, as model systems to study the AE. We showed that two different AE pathways exist in the transition of MSCs, which are determined by the MSCs’ compositions and structures. In addition, we achieved AE in two-dimensional nanocrystals, by which either type I or type II NPLs can be obtained without the Kirkendall effect. The heterostructured NPLs show improved optical properties. For example, the quantum efficiency of CdSe-CdS NPLs at 462 nm can be increased from 13.63% to 63.68%.