Making Rods out of Spheres

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Science  14 Nov 2003:
Vol. 302, Issue 5648, pp. 1117
DOI: 10.1126/science.302.5648.1117c

Semiconductor nanocrystals are of practical importance because their luminescent properties can be finely tuned by changing either the size or the shape of the particle, without needing to alter its composition. For example, rod-shaped particles show very different emissive properties than spherical ones, because the electrons and holes are no longer equally confined in all three directions.

Talapin et al. show that it is possible to grow rod-shaped shells of CdS on the outside of spherical CdSe cores by using an excess of sulfur and low temperatures during the shell growth process. As the sulfur preferentially interacts with certain facets of the CdSe nanocrystals, the CdS asymmetrically nucleates on the core. The photoluminescence of CdSe nanocrystals is enhanced by having a CdS shell, because electrons delocalize across the entire nanoparticle, whereas holes are more strongly confined to the cores. This results in a much larger Stokes shift (the difference in wavelength between the absorbed and emitted quanta) and increases the quantum yield because the emitted light is shifted to wavelengths where only the CdSe absorbs. — MSL

NanoLett. 10.1021/nl034815s (2003).

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