Dynamic Quantum-State Renormalization and Effects of Competing Pathways on Carrier Relaxation in Semiconductor Nanoparticles
Dynamic Quantum-State Renormalization and Effects of Competing Pathways on Carrier Relaxation in Semiconductor Nanoparticles
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DOI：
10.1021/acs.jpcc.3c05672
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发表时间：
2023-10-02
影响因子：
3.7
通讯作者：
Loomis，Richard A.
中科院分区：
文献类型：
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作者：
Chen，Jie;Sanderson，William M.;Loomis，Richard A.
在胶体半导体纳米粒子的瞬态吸收（TA）光谱测量中，探讨了光激发和电子屏蔽变化引起的量子态重整化（QSR）或量子约束态的能量转移的幅度和时间演化。在高质量和低质量的纤锌矿CdTe量子线（QWs）上进行了实验，在低激发影响下，光致发光量子产率分别为8.8%和~ 0.2%。QSR将两种样品的光谱特征转移到较低的能量，在高质量的qw中测量到较大的转移。光激发后，两种样品的TA光谱特征随时间发生独特的位移，说明动态QSR取决于量子约束态和载流子占据的态。在高质量量子阱中，达到带边态的载流子比例越高，重整化程度越高，带边态的能量接近稳态光致发光特征的Stokes位移，其能量低于带边吸收能量。在考虑了TA数据中QSR的贡献后，半导体纳米粒子中光激发的载流子带内弛豫动力学也得到了表征。高质量量子阱的带内弛豫比低质量量子阱的带内弛豫要慢，这可能是由于可进入的阱态数量减少。对比弛豫时间尺度为光致发光效率与激发能的依赖提供了明确的证据。这些研究揭示了半导体纳米颗粒中载流子的能量学和弛豫机制之间复杂的相互作用，即使是具有相同维度的载流子。
The magnitude and temporal evolution of the quantum-state renormalization (QSR), or the energetic shifting of the quantum-confinement states caused by photoexcitation and changes in electron screening, were probed in transient absorption (TA) spectroscopy measurements of colloidal semiconductor nanoparticles. Experiments were performed on high- and lower-quality wurtzite CdTe quantum wires (QWs) with photoluminescence quantum yields of 8.8% and ∼0.2% using low-excitation fluences. The QSR shifts the spectral features to lower energies in both samples, with larger shifts measured in the high-quality QWs. The TA spectral features measured for both samples shift uniquely with time after photoexcitation, illustrating dynamic QSR that depends on the quantum-confinement states and on the states occupied by carriers. The higher fraction of carriers that reach the band-edge states in the high-quality QWs results in larger renormalization, with the energies of the band-edge states approaching the Stokes shift of the steady-state photoluminescence feature below the band-edge absorption energy. The intraband relaxation dynamics of charge carriers photoexcited in semiconductor nanoparticles was also characterized after accounting for contributions from QSR in the TA data. The intraband relaxation to the band-edge states was slower in the high-quality QWs than in the lower-quality QWs, likely due to the reduced number of trap states accessible. The contrasting relaxation time scales provide definitive evidence for a dependence of the photoluminescence efficiency on excitation energy. These studies reveal the complicated interplay between the energetics and relaxation mechanisms of carriers within semiconductor nanoparticles, even those with the same dimensionality.