Electronic properties of aromatic hydrocarbons. III. Diffusion of excitons
Electronic properties of aromatic hydrocarbons. III. Diffusion of excitons
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芳香烃的电子特性。
DOI：
10.1098/rspa.1957.0008
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发表时间：
1957
期刊：
影响因子：
--
通讯作者：
O. Simpson
中科院分区：
文献类型：
--
作者：
O. Simpson
已知在某些绝缘晶体中由于基本吸收带中的激发而出现非导电激发态。受激区域称为激子。激子被认为是移动的并且能够通过晶体传输能量。在第二部分中，激子的迁移被证明给所观察到的转移荧光激发芳烃固溶体的定量解释。然而，与该领域的其他实验证据一样，激子运动本身是推断出来的，而不是观察到的。为了最终证明激子迁移，有必要测量扩散常数或扩散长度（D λ）1/2，其中λ是激发态的寿命。本文介绍了一种方法，通过该方法可以观察到激子在薄样品上的迁移，并给出了具有适当边界条件的扩散方程的解。该方法已被应用于实验蒽，激子通量作为距离的函数与理论一致。观察到的扩散长度为460 nm。在各向同性介质中，这将对应于激子的原点和衰变点之间的均方根位移f 1120 Ω。与第二部分的结果比较表明，在具有强各向异性的蒽中，激子的迁移最容易发生在相邻的b-c平面的分子之间，即在分子间迁移。e.垂直于石墨状结构中的薄层。
Non-conducting excited states are known to occur in certain insulating crystals as a result of excitation in the fundamental absorption band. The excited region is called an exciton. Excitons are believed to be mobile and capable of transporting energy through a crystal. In part II the migration of excitons was shown to give a quantitative explanation of the observed transfer of fluorescence excitation in solid solutions of aromatic hydrocarbons. However, in common with other experimental evidence in this field, the exciton motion itself was inferred rather than observed. To demonstrate exciton migration conclusively it is necessary to measure the diffusion constant, or the diffusion length (Dז)½ where ז is the lifetime of the excited state. In this paper a method is described by which the migration of excitons across a thin specimen can be observed, and solutions of the diffusion equation with the appropriate boundary conditions are shown. The method has been applied experimentally to anthracene, and the exciton flux as a function of distance agrees with the theory. The observed diffusion length is 460 Å. In an isotropic medium this would correspond to a root-mean-square displacement o f 1120 Å between the points of origin and decay of an exciton. Comparison with the results obtained in part II suggests that in anthracene, which is strongly anisotropic, the migration of excitons occurs most easily between molecules in adjacent b-c planes, i. e. normal to the laminae in the graphite-like structure.