Explanation of the Opposing Shifts in the Absorption Edge and the Optical Resonance in CuFeS 2 Nanoparticles
Explanation of the Opposing Shifts in the Absorption Edge and the Optical Resonance in CuFeS 2 Nanoparticles
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CuFeS 2 纳米粒子吸收边相对位移和光学共振的解释
DOI：
10.1021/acs.jpcc.1c07956
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Robinson, Richard D.
中科院分区：
文献类型：
--
作者：
Yao, Yuan;Biswas, Santu;Kang, Minsoo;Toroker, Maytal Caspary;Robinson, Richard D.
电子能带结构的尺寸依赖性变化是纳米粒子在量子约束区内的关键特征之一。cufes2纳米粒子在可见区有很强的吸收特性，有争议的是，它既不是激子跃迁，也不是自由载流子等离子振荡。相反，cufes2纳米颗粒中的吸收特征归因于价带（VB），中间带（IB）和导带（CB）之间带间跃迁的准静态光学共振。因此，我们假设该特征应该通过修改电子能带而受到量子限制效应的影响。实验表明，随着粒子尺寸的减小，光学共振吸收峰红移和光带隙蓝移。通过密度泛函理论（DFT）和紧密结合（TB）模型，我们阐明了带结构的大小依赖性，特别是关注IB的变化。利用洛伦兹振子光学模型模拟了从DFT计算的带结构和TB模型的带位移输入的吸收光谱。我们发现cufes2中光学共振峰位置的大小相关位移是由于三波段量子约束效应，导致VB到IB和IB到CB的间隙膨胀，同时伴随着粒径的减小。我们还发现，IB和CB之间的跃迁在光谱中只起很小的作用。此外，线性光学洛伦兹模型预测，通过部分填充IB，降低CB或扩大IB，可以在可见光范围内调节光学共振峰。
Size-dependent change of the electronic band structure is one of the key features of nanoparticles in the quantum confinement region. CuFeS2nanoparticles have a strong absorption feature in the visible region that has, controversially, been described as neither an excitonic transition nor a free carrier plasmon oscillation. Instead, the absorption feature in CuFeS2nanoparticles has been attributed to quasi-static optical resonances from inter-band transitions between the valence band (VB), intermediate band (IB), and conduction band (CB). As such, we hypothesized that the feature should be subject to quantum confinement effects through modification of the electronic bands. In this paper, we show experimentally that the optical resonance absorption peak red-shifts and the optical band gap blue-shifts as the particle size decreases. Through density functional theory (DFT) and the tight binding (TB) modeling, we elucidate the size dependence of the band structure, especially focusing on the change in the IB. Using a Lorentzian oscillator optical model to simulate the absorption spectrum with inputs from the DFT-calculated band structure and band shifts from the TB model, we find that the size-dependent shifts of the optical resonance peak position in CuFeS2are due to a tri-band quantum confinement effect that results in both the VB to IB and IB to CB gap expansion that accompanies a decrease in particle size. We also find that the transitions between the IB and CB play only a minor role in the optical spectrum. Moreover, the linear optical Lorentzian model predicts that the optical resonance peak is tunable across the visible range by partially filling the IB, lowering the CB, or expanding the IB.