Dynamics of Bound Exciton Complexes in CdS Nanobelts

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• 作者：Xinlong Xu ; Yanyuan Zhao ; Edbert Jarvis Sie ; Yunhao Lu ; Bo Liu ; Sandy Adhitia Ekahana ; Xiao Ju ; Qike Jiang ; Jianbo Wang ; Handong Sun ; Tze Chien Sum ; Cheng Hon Alfred Huan ; Yuan Ping Feng ; Qihua Xiong
• 刊名：ACS Nano
• 出版年：2011
• 出版时间：May 24, 2011
• 年：2011
• 卷：5
• 期：5
• 页码：3660-3669
• 全文大小：1054K
• 年卷期：0
• ISSN：1936-086X

文摘

Intrinsic defects such as vacancies, interstitials, and anti-sites often introduce rich luminescent properties in II−VI semiconductor nanomaterials. A clear understanding of the dynamics of the defect-related excitons is particularly important for the design and optimization of nanoscale optoelectronic devices. In this paper, low-temperature steady-state and time-resolved photoluminescence (PL) spectroscopies have been carried out to investigate the emission of cadmium sulfide (CdS) nanobelts that originates from the radiative recombination of excitons bound to neutral donors (I₂) and the spatially localized donor−acceptor pairs (DAP), in which the assignment is supported by first principle calculations. Our results verify that the shallow donors in CdS are contributed by sulfur vacancies while the acceptors are contributed by cadmium vacancies. At high excitation intensities, the DAP emission saturates and the PL is dominated by I₂ emission. Beyond a threshold power of approximately 5 μW, amplified spontaneous emission (ASE) of I₂ occurs. Further analysis shows that these intrinsic defects created long-lived (spin triplet) DAP trap states due to spin-polarized Cd vacancies which become saturated at intense carrier excitations.