Sequential growth of magic-size CdSe nanocrystals

Colloidal semiconductor nanocrystals have been exploited in several applications in which they serve as fluorophores, because of the tunability of the wavelength of the emitted light.[1-3] The possibility of exactly controlling the size of nanocrystals is of great importance in the development of these materials, as this will lead to nano-objects with well-defined and reproducible properties. Whereas this goal seems to be hard to achieve with large nanocrystals, it might be viable for clusters consisting of a few tens or hundreds of atoms, as in this size regime a handful of structures can have an exceptionally high stability and therefore would form preferentially over any other combination of atoms.

CdSe nanocrystals of well-defined sizes (so-called magic-size clusters, MSCs) have been grown with progressively larger sizes. During the synthesis, the relative populations of the different families of MSCs vary, as smaller clusters evolve into larger clusters. The time evolution of the various MSCs (see figure) is modeled by taking into account their much higher stability over nanocrystals of any intermediate size. A blue-light-emitting diode based on these MSCs is also presented.