Jakob Matthias, Aissiou Amira, Morrish William, Marsiglio Frank, Islam Muhammad, Kartouzian Aras, Meldrum Alkiviathes
Department of Chemistry, Technical University of Munich, Lichtenbergstrasse 4, 85748, Garching, Germany.
Department of Physics, University of Alberta, Edmonton, AB, T6G 2E1, Canada.
Nanoscale Res Lett. 2018 Nov 28;13(1):383. doi: 10.1186/s11671-018-2785-x.
The luminescence dynamics in ensembles of nanocrystals are complicated by a variety of processes, including the size-dependence of the radiative and non-radiative rates in inhomogeneous broadened samples and interparticle interactions. This results in a non-exponential decay, which for the specific case of silicon nanocrystals (SiNCs) has been widely modeled with a Kohlrausch or "stretched exponential" (SE) function. We first derive the population decay function for a luminescence decay following exp[- (t/τ)]. We then compare the distributions and mean times calculated by assuming that either the luminescence decay or the population decay follows this function and show that the results are significantly different for β much below 1. We then apply these two types of SE functions as well as other models to the luminescence decay data from two thermally grown SiNC samples with different mean sizes. The mean lifetimes are strongly dependent on the experimental setup and the chosen fitting model, none of which appears to adequately describe the ensemble decay dynamics. Frequency-resolved spectroscopy (FRS) techniques are then applied to SiNCs in order to extract the lifetime distribution directly. The rate distribution has a half width of ~ 0.5 decades and mainly resembles a somewhat high-frequency-skewed lognormal function. The combination of TRS and FRS methods appear best suited to uncovering the luminescence dynamics of NC materials having a broad emission spectrum.
纳米晶体集合体中的发光动力学因多种过程而变得复杂，这些过程包括非均匀展宽样品中辐射和非辐射速率的尺寸依赖性以及粒子间相互作用。这导致了非指数衰减，对于硅纳米晶体（SiNCs）的特定情况，已广泛使用科尔劳施或“拉伸指数”（SE）函数进行建模。我们首先推导了遵循exp[- (t/τ)]的发光衰减的粒子数衰减函数。然后，我们比较了在假设发光衰减或粒子数衰减遵循该函数的情况下计算出的分布和平均时间，并表明当β远低于1时，结果有显著差异。然后，我们将这两种类型的SE函数以及其他模型应用于来自两个具有不同平均尺寸的热生长SiNC样品的发光衰减数据。平均寿命强烈依赖于实验装置和所选的拟合模型，似乎没有一种模型能充分描述集合体的衰减动力学。然后将频率分辨光谱（FRS）技术应用于SiNCs，以直接提取寿命分布。速率分布的半高宽约为0.5个数量级，主要类似于某种高频偏态对数正态函数。时间分辨光谱（TRS）和FRS方法的结合似乎最适合揭示具有宽发射光谱的纳米晶体材料的发光动力学。
