Kocevski V, Eriksson O, Gerard C, Sarma D D, Rusz J
Department of Physics and Astronomy, Uppsala University, P.O. Box 516, S-751 20 Uppsala, Sweden.
J Chem Phys. 2015 Oct 28;143(16):164701. doi: 10.1063/1.4933058.
Semiconducting nanocrystals (NCs) have become one of the leading materials in a variety of applications, mainly due to their size tunable band gap and high intensity emission. Their photoluminescence (PL) properties can be notably improved by capping the nanocrystals with a shell of another semiconductor, making core-shell structures. We focus our study on the CdS/ZnS core-shell nanocrystals that are closely related to extensively studied CdSe/CdS NCs, albeit exhibiting rather different photoluminescence properties. We employ density functional theory to investigate the changes in the electronic and optical properties of these nanocrystals with size, core/shell ratio, and interface structure between the core and the shell. We have found that both the lowest unoccupied eigenstate (LUES) and the highest occupied eigenstate (HOES) wavefunction (WF) are localized in the core of the NCs, with the distribution of the LUES WF being more sensitive to the size and the core/shell ratio. We show that the radiative lifetimes are increasing, and the Coulomb interaction energies decrease with increasing NC size. Furthermore, we investigated the electronic and optical properties of the NCs with different interfaces between the core and the shell and different core types. We find that the different interfaces and core types have rather small influence on the band gaps and the absorption indexes, as well as on the confinement of the HOES and LUES WFs. Also the radiative lifetimes are found to be only slightly influenced by the different structural models. In addition, we compare these results with the previous results for CdSe/CdS NCs, reflecting the different PL properties of these two types of NCs. We argue that the difference in their Coulomb interaction energies is one of the main reasons for their distinct PL properties.
半导体纳米晶体（NCs）已成为多种应用中的主要材料之一，这主要归功于其尺寸可调的带隙和高强度发射。通过用另一种半导体壳层包覆纳米晶体形成核壳结构，其光致发光（PL）特性可得到显著改善。我们的研究重点是与广泛研究的CdSe/CdS NCs密切相关的CdS/ZnS核壳纳米晶体，尽管它们表现出相当不同的光致发光特性。我们采用密度泛函理论来研究这些纳米晶体的电子和光学性质随尺寸、核/壳比以及核与壳之间界面结构的变化。我们发现最低未占据本征态（LUES）和最高占据本征态（HOES）的波函数（WF）都局域在纳米晶体的核中，LUES WF的分布对尺寸和核/壳比更敏感。我们表明，随着纳米晶体尺寸的增加，辐射寿命增加，库仑相互作用能降低。此外，我们研究了核与壳之间具有不同界面以及不同核类型的纳米晶体的电子和光学性质。我们发现不同的界面和核类型对带隙、吸收指数以及HOES和LUES WFs的限制影响相当小。辐射寿命也仅受到不同结构模型的轻微影响。此外，我们将这些结果与之前关于CdSe/CdS NCs的结果进行比较，反映了这两种类型纳米晶体不同的PL特性。我们认为它们库仑相互作用能的差异是其不同PL特性的主要原因之一。
