Transient Absorption Spectroscopy of CdSe Nanoplatelets
Transient Absorption Spectroscopy of CdSe Nanoplatelets
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DOI：
10.1021/acs.jpcc.8b07733
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发表时间：
2018-10-18
影响因子：
3.7
通讯作者：
Kelley, David F.
中科院分区：
文献类型：
--
作者：
Morgan, David P.;Maddux, Cassandra J. A.;Kelley, David F.
根据重空穴电子结构分析了4.5单层厚的CdSe纳米片的瞬态吸收谱。纳米片处理与4-甲基苯乙胺（MBT），空穴受体，和光谱和动力学与和没有MBT进行比较，以评估的TA光谱中的价带状态填充的作用。类似的TA光谱获得球形的CdSe量子点，表明价带空穴的存在下产生定性不同的行为在球形与二维（2D）纳米粒子的情况下。在量子点中，激子到IF双激子跃迁是完全允许的，并且具有与带负电荷的粒子到负trion跃迁接近相同的能量和振子强度，45%-55%，这导致在TA w/o空穴陷阱w/空穴陷阱测量中没有看到任何空穴动力学。在片晶的情况下，大的形状各向异性分裂解除轻/重空穴简并，导致从最低空穴能级的激子到双激子的跃迁被禁止。激子波函数的较大空间范围也降低了交换相互作用，导致亮激子态的显著布居。结果表明，受激发射对重空穴漂白带的振幅有显著的贡献，而重空穴跃迁的光致吸收的振幅对导带和价带态的填充都很敏感.
Transient absorption (TA) spectra of 4.5 monolayer thick CdSe nanoplatelets are analyzed in terms of the heavy hole electronic structure. The nanoplatelets are treated with 4-methylbenzenethiol (MBT), a hole acceptor, and the spectra and kinetics with and without MBT are compared in order to assess the role of valence band state filling in the TA spectra. Analogous TA spectra are obtained for spherical CdSe quantum dots, showing that the presence of a valence band hole produces qualitatively different behavior in the spherical vs two-dimensional (2D) nanoparticle cases. In quantum dots, the exciton to IF biexciton transition is fully allowed and has close to the same energy and oscillator strength as the negatively charged particle to negative trion transition, 45% 55% which leads to the absence of any hole dynamics being seen in TA w/o hole trap w/ hole trap measurements. In the case of the platelets, the large shape anisotropy splitting lifts the light/heavy hole degeneracy, causing the exciton to biexciton transition from the lowest hole level to be forbidden. The larger spatial extent of the excitonic wave functions also reduces the exchange interaction, leading to significant population of the bright exciton state. As a result, stimulated emission significantly contributes to the amplitude of the heavy hole bleach band, and the amplitude of the photoinduced absorption of the heavy hole transition is sensitive to both conduction band and valence band state filling.