Ligand-Controlled Polytypism of Thick-Shell CdSe/CdS Nanocrystals

摘要

Abstract: We report the synthesis of CdSe/CdS semiconductor core/shell nanocrystals with very thick (5nnm) CdS shells. As in the case of core CdSe nanocrystals, we show that a thick-shell CdSe/CdS coreshell structure can be synthesized in either a pure wurtzite (W) or a zinc-blende (ZB) crystal structure.nWhile the growth of thick-shell wurtzite CdSe/CdS is quite straightforward, we observe that the growth ofna CdS shell on zinc-blende CdSe cores is more difficult and leads to wurtzite/zinc-blende polytypism whennprimary amines are present during the shell formation. Using absorption spectra analysis to differentiatenzinc blende from wurtzite CdSe, we show that primary amines can induce a nearly complete structuralntransformation of CdSe ZB cores into W cores. This better understanding of the CdSe ligand-dependentncrystal structural evolution during shell growth is further used to grow large (10 nm)-diameter perfect zinc-nblende CdSe core crystals emitting above 700 nm, and perfect ZB thick-shell CdSe/CdS nanocrystals. Wenobserved that all thick-shell CdSe/CdS QDs have extremely reduced blinking events compared to thin-nshell QDs, without any significant influence of crystalline structure and polytypism.