Department of Chemistry, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
Nano Lett. 2016 Oct 12;16(10):6070-6077. doi: 10.1021/acs.nanolett.6b02147. Epub 2016 Sep 16.
Lead chalcogenide colloidal nanocrystals (NCs) are promising materials for solution processable optoelectronics. However, there is little agreement on the identity and character of PbS NC emission for different degrees of quantum confinement-a critical parameter for realizing applications for these nanocrystals. In this work, we combine ensemble and single NC spectroscopies to interrogate preparations of lead sulfide NCs. We use solution photon correlation Fourier spectroscopy (S-PCFS) to measure the average single NC linewidth of near-infrared-emitting PbS quantum dots and find it to be dominated by homogeneous broadening. We further characterize PbS NCs using temperature-dependent linear and time-resolved emission spectroscopy which demonstrate that a kinetically accessed defect state dominates room temperature emission of highly confined emitting NCs. These experiments, taken together, demonstrate that the linewidth and Stokes shift of PbS NCs are the result of emission from two states: a thermally accessed defect-with an energetically pinned charge carrier-and an inhomogeneously broadened band-edge state.
铅的硫属化物胶体纳米晶体（NCs）是一种很有前途的溶液处理型光电材料。然而，对于不同程度的量子限制（实现这些纳米晶体应用的关键参数）下 PbS NC 发射的性质和特征，人们还没有达成共识。在这项工作中，我们结合了集体和单 NC 光谱学来研究硫化铅 NCs 的制备。我们使用溶液光子相关傅里叶光谱学（S-PCFS）来测量近红外发射 PbS 量子点的平均单 NC 线宽，并发现它主要由均匀展宽决定。我们进一步使用温度依赖的线性和时间分辨发射光谱来表征 PbS NCs，这些实验表明，动力学上可访问的缺陷态主导了高度受限发射 NCs 的室温发射。这些实验共同表明，PbS NCs 的线宽和斯托克斯位移是来自两个态的发射结果：一个是热访问的缺陷，其载流子的电荷被能量固定；另一个是不均匀展宽的能带边缘态。
