Photoluminescence of Ag-In-S/ZnS quantum dots: Excitation energy dependence and low-energy electronic structure
Photoluminescence of Ag-In-S/ZnS quantum dots: Excitation energy dependence and low-energy electronic structure
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DOI：
10.1007/s12274-019-2398-4
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发表时间：
2019-07-01
期刊：
影响因子：
9.9
通讯作者：
Resch-Genger, Ute
中科院分区：
文献类型：
--
作者：
Martynenko, Irina V.;Baimuratov, Anvar S.;Resch-Genger, Ute
无Cd的I-III-VI族半导体量子点（QD）如Ag-In-S和Cu-In-S显示具有明显Urbach尾的非结构化吸收光谱，使得难以确定它们的带隙能量（E-g）和激子的能量结构。此外，寿命为几百纳秒的宽光致发光（PL）带的起源仍有争议。这鼓励我们研究激发能依赖性（EED）的PL最大值，PL光谱带宽，量子产率（QY），和衰减动力学的AIS/ZnS量子点的不同大小，组成，和表面封端配体。然后将这些结果与相应吸收光谱的二阶导数相关联。PL谱带位置和光谱宽度的变化与吸收光谱的二阶导数的最小值之间的良好匹配强调了EED方法用于从PL数据导出这些三元QD的E-g值的潜力。然而，在研究的能量范围内，PL QY与激发能无关。从AIS/ZnS量子点的光致发光特征的EED，我们还可以推导出低能电子结构的形成机制。这另外通过比较合成的和尺寸选择的QD系综的PL数据的EED以及这些PL数据与单个QD的PL光谱的比较来证实。这些结果表明，一个强大的贡献内在的不均匀PL加宽AIS/ZnS量子点的整体发射功能，从辐射跃迁从一组能量状态的缺陷定位在量子点体积内的不同位置，除了从尺寸和化学加宽的贡献。通过采用球形量子点的简单质量近似和修改的供体-受体模型对吸收和PL能量进行数值建模来证实这种机制，从而利用了之前提出的三元量子点PL机制的优点。这些发现将为深入理解量子限制的I-III-VI族半导体纳米材料中PL的性质铺平道路。
Cd-free I-III-VI group semiconductor quantum dots (QDs) like Ag-In-S and Cu-In-S show unstructured absorption spectra with a pronounced Urbach tail, rendering the determination of their band gap energy (E-g) and the energy structure of the exciton difficult. Additionally, the origin of the broad photoluminescence (PL) band with lifetimes of several hundred nanoseconds is still debated. This encouraged us to study the excitation energy dependence (EED) of the PL maxima, PL spectral band widths, quantum yields (QYs), and decay kinetics of AIS/ZnS QDs of different size, composition, and surface capping ligands. These results were then correlated with the second derivatives of the corresponding absorption spectra. The excellent match between the onset of changes in PL band position and spectral width with the minima found for the second derivatives of the absorption spectra underlines the potential of the EED approach for deriving E-g values of these ternary QDs from PL data. The PL QY is, however, independent of excitation energy in the energy range studied. From the EED of the PL features of the AIS/ZnS QDs we could also derive a mechanism of the formation of the low-energy electronic structure. This was additionally confirmed by a comparison of the EED of PL data of as-synthesized and size-selected QD ensembles and the comparison of these PL data with PL spectra of single QDs. These results indicate a strong contribution of intrinsic inhomogeneous PL broadening to the overall emission features of AIS/ZnS QDs originating from radiative transitions from a set of energy states of defects localized at different positions within the quantum dot volume, in addition to contributions from dimensional and chemical broadening. This mechanism was confirmed by numerically modelling the absorption and PL energies with a simple mass approximation for spherical QDs and a modified donor-acceptor model, thereby utilizing the advantages of previously proposed PL mechanisms of ternary QDs. These findings will pave the road to a deeper understanding of the nature of PL in quantum confined I-III-VI group semiconductor nanomaterials.