Luminescent CuInS₂ (CIS) quantum dots (QDs) exhibit highly efficient intragap emission and long, hundreds-of-nanoseconds radiative lifetimes. These spectral properties, distinct from structurally similar II–VI QDs, can be explained by the involvement of intragap defect states containing a localized hole capable of coupling with a conduction band electron for a radiative transition. However, the absolute energies of the intragap and band-edge states, the structure of the emissive defect(s), and the role and origin of nonemissive decay channels still remain poorly understood. Here, we address these questions by applying methods of spectral electrochemistry. Cyclic voltammetry measurements reveal a well-defined intragap state whose redox potential is close to that of the Cu^x defect state (where x = 1+ or 2+). The energy offset of this state from the valence band accounts well for the apparent photoluminescence Stokes shift observed in optical spectra. These results provide direct evidence that Cu-related defects serve as emission centers responsible for strong intragap emission from CIS QDs. We then use in situ spectroelectrochemistry to reveal two distinct emission pathways based on the differing oxidation states of Cu defects, which can be controlled by altering QD stoichiometry (1+ for stoichiometric QDs and 2+ for Cu-deficient QDs).

中文翻译：

---

光谱电化学评价CuInS ₂量子点中的发光机理

发光的CuInS ₂（CIS）量子点（QD）表现出高效的能隙内发射和长百纳秒的辐射寿命。这些光谱特性与结构相似的II–VI QD不同，可以通过间隙内缺陷状态的参与来解释，该缺陷状态包含一个能够与导带电子耦合以进行辐射跃迁的局部空穴。然而，间隙内和带边缘态的绝对能量，发射缺陷的结构以及非发射衰变通道的作用和起源仍然知之甚少。在这里，我们通过应用光谱电化学方法解决这些问题。循环伏安法测量显示出明确定义的能隙内部状态，其氧化还原电势接近Cu ^x的电势缺陷状态（其中x = 1+或2+）。该状态从价带的能量偏移很好地解释了在光谱中观察到的表观光致发光斯托克斯位移。这些结果提供了直接的证据，证明与铜有关的缺陷是导致CIS量子点产生强烈的间隙内发射的发射中心。然后，我们使用原位光谱电化学来揭示基于铜缺陷不同氧化态的两个不同的发射途径，可以通过改变QD化学计量来控制（化学计量QD为1+，而缺铜QD为2+）。