Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA.
J Am Chem Soc. 2011 Nov 2;133(43):17504-12. doi: 10.1021/ja208337r. Epub 2011 Oct 10.
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 2S(h3/2)1S(e) 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.
我们基于配体交换化学、同材质核/壳生长、光学光谱学、透射电子显微镜和 X 射线粉末衍射研究了 II-VI 闪锌矿半导体纳米晶体的表面功能化依赖性光学性质。我们的结果表明，这些纳米晶体的 2S(h3/2)1S(e)激子带的跃迁能量和消光系数可以通过它们的表面配体以及配体相关的表面原子排列强烈地修饰。油酸酯封端的闪锌矿 II-VI 纳米晶体的油胺交换缩小了它们的第一和第二激子吸收带之间的能隙，并且这种缩小效应是尺寸依赖性的。油胺交换导致这些 II-VI 半导体纳米晶体的光致发光发射猝灭、随后恢复，甚至增强。此外，我们的 X 射线粉末衍射测量和模拟结果完全排除了油酸酯封端的闪锌矿 CdSe 纳米晶体在与油胺配体交换时可能发生闪锌矿到纤锌矿晶体转变的可能性。此外，我们的理论建模结果表明，这些半导体纳米晶体的表面功能化依赖性光学性质可能是由带负电荷的配体（例如油酸和十八烷基膦酸酯）形成的薄型 II 型同材质壳引起的。综合所有这些结果，我们明确地鉴定出 II-VI 半导体纳米晶体表现出表面功能化依赖性的激子吸收特征。
