Instituto de Fisica "GlebWataghin" , Universidade Estadual de Campinas, UNICAMP , P.O. Box 6165 , 13083-859 Campinas, Sao Paulo , Brazil.
UbiQD, Inc. , 134 Eastgate Drive , Los Alamos , New Mexico 87544 , United States.
Nano Lett. 2018 Oct 10;18(10):6353-6359. doi: 10.1021/acs.nanolett.8b02707. Epub 2018 Sep 17.
CuInS (CIS) quantum dots (QDs) have emerged as one of the most promising candidates for application in a number of new technologies, mostly due to their heavy-metal-free composition and their unique optical properties. Among those, the large Stokes shift and the long-lived excited state are the most striking ones. Although these properties are important, the physical mechanism that originates them is still under debate. Here, we use two-photon absorption spectroscopy and ultrafast dynamics studies to investigate the physical origin of those phenomena. From the two-photon absorption spectroscopy, we observe yet another unique property of CIS QDs, a two-photon absorption transition below the one-photon absorption band edge, which has never been observed before for any other semiconductor nanostructure. This originates from the inversion of the 1S and 1P hole level order at the top of the valence band and results in a blue-shift of the experimentally measured one photon absorption edge by nearly 100 to 200 meV. However, this shift is not large enough to account for the Stokes shift observed, 200-500 meV. Consequently, despite the existence of the below band gap optical transition, photoluminescence in CIS QDs must originate from trap sites. These conclusions are reinforced by the multiexciton dynamics studies. From those, we demonstrate that biexciton Auger recombination behaves similarly to negative trion dynamics on these nanomaterials, which suggests that the trap state is an electron donating site.
铜铟硫（CIS）量子点（QD）由于其不含重金属的组成和独特的光学性质，已成为许多新技术应用中最有前途的候选材料之一。其中，大斯托克斯位移和长寿命激发态是最引人注目的特性。尽管这些特性很重要，但它们的物理起源仍存在争议。在这里，我们使用双光子吸收光谱和超快动力学研究来研究这些现象的物理起源。从双光子吸收光谱中，我们观察到 CIS QD 的另一个独特性质，即在单光子吸收带边缘以下存在双光子吸收跃迁，这在以前从未观察到过任何其他半导体纳米结构中出现过。这源于价带顶部 1S 和 1P 空穴能级的反转，导致实验测量的单光子吸收边缘蓝移近 100 到 200 毫电子伏特。然而，这种位移不足以解释观察到的斯托克斯位移，即 200-500 毫电子伏特。因此，尽管存在带隙下的光学跃迁，但 CIS QD 中的光致发光必须源自陷阱位置。这些结论得到了多激子动力学研究的支持。从这些研究中，我们证明了双激子俄歇复合与这些纳米材料上的负三价离子动力学相似，这表明陷阱态是一个电子供体位置。
