Charge Separation by Indirect Bandgap Transitions in CdS/ZnSe Type-II Core/Shell Quantum Dots
Charge Separation by Indirect Bandgap Transitions in CdS/ZnSe Type-II Core/Shell Quantum Dots
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DOI：
10.1021/jp400014j
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发表时间：
2013-05
影响因子：
3.7
通讯作者：
S. Verma;S. Kaniyankandy;H. Ghosh
中科院分区：
文献类型：
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作者：
S. Verma;S. Kaniyankandy;H. Ghosh
用飞秒时间分辨吸收和皮秒时间分辨发射研究了CdS/ZnSe核/壳量子点的间接型激子。随着硫化锌壳层厚度的增加，制备了硫化镉/锌硒核/壳量子点样品。在这些CdS/ZnSe核壳样品中，观察到了一个新的低于CdS壳和ZnSe壳的能隙的新能带，这归因于从ZnSe壳层的价带到CDS核的导带的间接带隙跃迁。瞬时光致发光研究表明，由于光激发低能带而产生的间接型激子e(Cds)/h(ZnSe)，在交错的光激发态下，比起选择性地激发cdS芯和电荷转移，它所经历的载流子捕获和电荷转移更少。飞秒瞬时吸收研究表明，在CdS中，载流子捕获速度高达100fs，界面电荷复合速度随着CdS QD上ZnSe壳层厚度的增加而减慢。
Femtosecond time-resolved absorption and picosecond time-resolved emission studies have been carried out to study the indirect type exciton of CdS/ZnSe core/shell quantum dots (QDs). The CdS/ZnSe core/shell QD samples are synthesized with increasing thickness of ZnSe shell on CdS core QDs. In these CdS/ZnSe core/shell samples, a new energy band lower than the energy gap of both the CdS core and ZnSe shell has been observed and attributed to indirect bandgap transitions from the valence band of the ZnSe shell to the conduction band of the CdS core. The transient PL studies have revealed that the indirect type exciton, e(CdS)/h(ZnSe) due to photoexcitation of this low-energy band, endures less carrier trapping than selective excitation of the CdS core and charge transfer in the staggered photoexcited state. Femtosecond transient absorption studies have revealed that carrier trapping is as fast as 100 fs and interfacial charge recombination slows down with increasing ZnSe shell thickness on the CdS QD in CdS...