Ion exchange of nanocrystals has the potential to emerge as an alternative to conventional routes for synthesis of ionic nanocrystals. The facile ability to replace all cations of a nanocrystal with another cation, while preserving size and shape, allows us to employ nanocrystals as templates for the fabrication of other nanocrystals of interest. Such a tem-plated synthesis strategy is especially useful when the chemistry or crystallographic phase of the target nanocrystals is difficult to access via hot-injection methods. For instance, we recently showed that Cu~I sulfide quantum dots prepared by hot injection mostly result in the highly Cu-deficient djurleite phase. The stoichiometric chalcocite phase is achievable, however, by room-temperature cation exchange of template CdS quantum dots with Cu~+ ions.
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