Although surface ligands of colloidal nanocrystals are known to adjust the absolute energy levels of valence and conduction bands of semiconductor nanocrystals, they typically have only minor influence on the band gap or effective masses. This changes in nanoplatelets. Ligand exchange of CdSe colloidal nanoplatelets induces large (up to 300 meV) bathochromic shifts of both interband and intersubband transitions. Here, three families of ligands—halides, thiolates, and phosphonates—are used to tune interband transitions, reflecting electron and hole confinement, across visible wavelengths and intersubband transitions, reflecting electron confinement, across the near-infrared spectral window. Careful examination shows that delocalization from expansion of the nanoplatelet short axis, which was reported previously, cannot alone explain observed red shifts. Instead, comparison of intersubband, interband, and hole energy levels shows that ligand head group chemistry confers specific, idiosyncratic adjustments of the contribution of conduction and valence bands to the observed bathochromic shifts. Phosphonate ligands show the largest band gap reductions but the smallest red shift of intersubband transition energies; halide-exchanged samples displayed smaller reductions in band gap but large red shifts of intersubband transitions; thiolates fall in between. A related specificity is observed in hole states, which implicates ligand-responsive valence band curvature as an additional contribution driving optical changes. For nanoplatelets, surface ligand chemistry offers not only a tool to adjust the absolute energy level of conduction and valence bands but also an alternative route to preferential electron or hole band engineering that is normally achieved with inorganic shells.

中文翻译：

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胶体CdSe纳米片的带间和子带间过渡的配体依赖性调谐

尽管已知胶态纳米晶体的表面配体可调节半导体纳米晶体的价和导带的绝对能级，但它们通常对带隙或有效质量的影响很小。这改变了纳米血小板。CdSe胶体纳米血小板的配体交换会引起带间和子带间过渡的大（高达300 meV）红移。在这里，三个配体族（卤化物，硫醇盐和膦酸酯）用于调整能带间的跃迁，在可见光波长范围内反映电子和空穴的束缚，并在近红外光谱窗口内反映电子和空穴的跃迁，反映电子的束缚。仔细的检查显示，纳米血小板短轴的扩张引起了离域，这是先前报道的，不能单独解释观察到的红移。相反，子带间，带间和空穴能级的比较表明，配体头基化学赋予传导带和价带对观察到的红移的贡献特定的，特殊的调整。膦酸酯配体显示出最大的带隙减小量，但子带间跃迁能量的红移最小。卤化物交换的样品带隙减小较小，但子带间跃迁的红移较大；硫醇盐介于两者之间。在空穴状态中观察到相关的特异性，这暗示配体响应价带曲率是驱动光学变化的额外贡献。对于纳米血小板，