Surface-Functionalization-Dependent Optical Properties of II–VI Semiconductor Nanocrystals

• Published in: Journal of the American Chemical Society Vol. 133; no. 43; pp. 17504 - 17512
• Main Authors: Chen, Ou, Yang, Yongan, Wang, Tie, Wu, Huimeng, Niu, Chenggang, Yang, Jianhui, Cao, Y. Charles
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.11.2011
• Subjects: Nanoparticles - chemistry; Optics and Photonics; Semiconductors; Surface Properties
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/ja208337r

We report a study of the surface-functionalization-dependent optical properties of II–VI zinc-blende semiconductor nanocrystals on the basis of ligand-exchange chemistry, isomaterial core/shell growth, optical spectroscopy, transmission electron microscopy, and X-ray powder diffraction. Our results show that the transition energy and extinction coefficient of the 2Sh3/21Se excitonic band of these nanocrystals can be strongly modified by their surface ligands as well as ligand associated surface atomic arrangement. The oleylamine exchange of oleate-capped zinc-blende II–VI nanocrystals narrows the energy gap between their first and second excitonic absorption bands, and this narrowing effect is size-dependent. The oleylamine exchange results in the quenching, subsequent recovery, and even enhancing of the photoluminescence emission of these II–VI semiconductor nanocrystals. In addition, the results from our X-ray powder diffraction measurements and simulations completely rule out the possibility that oleate-capped zinc-blende CdSe nanocrystals can undergo zinc-blende-to-wurtzite crystal transformation upon ligand exchange with oleylamine. Moreover, our theoretical modeling results suggest that the surface-functionalization-dependent optical properties of these semiconductor nanocrystals can be caused by a thin type II isomaterial shell that is created by the negatively charged ligands (e.g., oleate and octadecyl phosphonate). Taking all these results together, we provide the unambiguous identification that II–VI semiconductor nanocrystals exhibit surface-functionalization-dependent excitonic absorption features.