Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
J Phys Chem B. 2013 Sep 19;117(37):10869-82. doi: 10.1021/jp405578w. Epub 2013 Aug 21.
Crystalloluminescence, the long-lived emission of visible light during the crystallization of certain salts, was first observed over 200 years ago; however, the origin of this luminescence is still not well understood. The observations suggest that the process of crystallization may not be purely classical but also involves an essential electronic structure component. Strong electric field fluctuations may play an important role in this process by providing the necessary driving force for the observed electronic structure changes. The main objective of this work is to provide a basic understanding of the fluctuations in charge, electric potentials, and electric fields for concentrated aqueous NaCl electrolytes. Our charge analysis reveals that the water molecules in the first solvation shell of the ions serve as a sink for electron density originating on Cl(-). We find that the electric fields inside aqueous electrolytes are extremely large (up to several V/Å) and thus may alter the ground and excited electronic states in the condensed phase. Furthermore, our results show that the potential and field distributions are largely independent of concentration. We also find the field component distributions to be Gaussian for the ions and non-Gaussian for the O and H sites (computed in the lab frame of reference), however, these non-Gaussian distributions are readily modeled via an orientationally averaged nonzero mean Gaussian plus a zero mean Gaussian. These calculations and analyses provide the first steps toward understanding the magnitude and fluctuations of charge, electric potentials, and fields in aqueous electrolytes and what role these fields may play in driving charge redistribution/transfer during crystalloluminescence.
结晶发光，即在某些盐类结晶过程中可见光线的长时间发射，早在 200 多年前就首次被观察到；然而，这种发光的起源仍然没有得到很好的理解。这些观察表明，结晶过程可能不仅是纯粹的经典过程，还涉及到基本的电子结构组成部分。强电场波动可能通过为观察到的电子结构变化提供必要的驱动力，在这个过程中发挥重要作用。这项工作的主要目的是为浓水溶液中 NaCl 电解质的电荷、电势和电场波动提供基本的理解。我们的电荷分析表明，离子的第一溶剂化壳层中的水分子是来自 Cl(-)的电子密度的汇。我们发现，水溶液中的电场非常大（高达几伏特/埃），因此可能会改变凝聚相中的基态和激发态电子态。此外，我们的结果表明，电势和场分布在很大程度上与浓度无关。我们还发现，对于离子，场分量分布是高斯分布，而对于 O 和 H 位，则是非高斯分布（在实验室参考系中计算），然而，这些非高斯分布可以通过一个具有非零平均的各向同性高斯分布加上一个零平均高斯分布来很好地建模。这些计算和分析为理解水溶液电解质中的电荷、电势和电场的大小和波动以及这些电场在结晶发光过程中驱动电荷重新分布/转移中可能扮演的角色提供了第一步。
