Abstract

This work studies extinction properties of ZnSe quantum dots terminated with either Se-surface or Zn-surface (Se-ZnSe or Zn-ZnSe QDs). In addition to commonly observed photoluminescence quenching by anionic surface sites, Se-ZnSe QDs are found to show drastic signatures of Se-surface states in their UV-visible (Vis) absorption spectra. Similar to most QDs reported in literature, monodisperse Zn-ZnSe QDs show sharp absorption features and blue-shifted yet steep absorption edge respect to the bulk bandgap. However, for monodisperse Se-ZnSe QDs, all absorption features are smeared and a low-energy tail is identified to extend to an energy window below the bulk ZnSe bandgap. Along increasing their size, a cyclic growth of ZnSe QDs switches their surface from Zn-terminated to Se-terminated ones, which confirms that the specific absorption signatures are reproducibly repeated between those of two types of the QDs. Though the extinction coefficients per unit of Se-ZnSe QDs are always larger than those of Zn-ZnSe QDs with the same size, both of them approach the same bulk limit. In addition to contribution of the lattice, extinction coefficients per nanocrystal of Zn-ZnSe QDs show an exponential term against their sizes, which is expected for quantum-confinement enhancement of electron-hole wavefunction overlapping. For Se-ZnSe QDs, there is the third term identified for their extinction coefficients per nanocrystal, which is proportional to the square of size of the QDs and consistent with surface contribution.

中文翻译：

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ZnSe量子点消光特性的表面和内在贡献

摘要

这项工作研究了以Se表面或Zn表面终止的ZnSe量子点（Se-ZnSe或Zn-ZnSe QDs）的消光特性。除了通常观察到的通过阴离子表面位点猝灭光致发光外，还发现Se-ZnSe QD在其UV-可见（Vis）吸收光谱中显示出Se-表面态的剧烈特征。与文献中报道的大多数QD相似，单分散Zn-ZnSe QD显示出相对于整体带隙的尖锐吸收特性和蓝移但陡峭的吸收边缘。但是，对于单分散的Se-ZnSe QD，所有吸收特征都被涂抹了，并且发现了低能量的尾部延伸到整体ZnSe带隙以下的能量窗口。随着尺寸的增加，ZnSe QD的循环生长将其表面从Zn端基转变为Se端基，这证实了特定的吸收特征在两种类型的量子点之间可重复地重复。尽管Se-ZnSe量子点的单位消光系数总是大于相同尺寸的Zn-ZnSe量子点的消光系数，但它们的体积极限都相同。除了晶格的贡献外，Zn-ZnSe量子点的每个纳米晶体的消光系数还显示出与其大小有关的指数项，这有望增强电子-空穴波函数重叠的量子限制。对于Se-ZnSe量子点，每个纳米晶体的消光系数都有第三个项，它与量子点大小的平方成正比，并且与表面贡献一致。尽管Se-ZnSe量子点的单位消光系数总是大于相同尺寸的Zn-ZnSe量子点的消光系数，但它们的体积极限都相同。除了晶格的贡献外，Zn-ZnSe量子点的每个纳米晶体的消光系数还显示出与其大小有关的指数项，这有望增强电子-空穴波函数重叠的量子限制。对于Se-ZnSe量子点，每个纳米晶体的消光系数都有第三个项，它与量子点大小的平方成正比，并且与表面贡献一致。尽管Se-ZnSe量子点的单位消光系数总是大于相同尺寸的Zn-ZnSe量子点的消光系数，但它们的体积极限都相同。除了晶格的贡献外，Zn-ZnSe量子点的每个纳米晶体的消光系数还显示出与其大小有关的指数项，这有望增强电子-空穴波函数重叠的量子限制。对于Se-ZnSe量子点，每个纳米晶体的消光系数都有第三个项，它与量子点大小的平方成正比，并且与表面贡献一致。有望增强电子-空穴波函数重叠的量子约束。对于Se-ZnSe量子点，每个纳米晶体的消光系数都有第三个项，它与量子点大小的平方成正比，并且与表面贡献一致。有望增强电子-空穴波函数重叠的量子约束。对于Se-ZnSe量子点，存在每个纳米晶体的消光系数，它们与量子点尺寸的平方成正比，并且与表面贡献一致，因此存在第三个术语。