Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States.
J Phys Chem B. 2013 Dec 12;117(49):15257-71. doi: 10.1021/jp405785a. Epub 2013 Sep 9.
The nonradiative relaxation of both the exciton and biexciton in CdSe/ZnS core-shell nanoparticles have complicated, nonexponential kinetics. This paper presents data on this system from multiple population-period transient spectroscopy (MUPPETS), a method for two-dimensional kinetics. An initial report of a dispersed (nonexponential) biexciton decay [J. Am. Chem. Soc. 2013, 135, 1002] is confirmed in a more rigorous analysis. Additional transient-grating data allow a quantitative treatment of the full, complex MUPPETS data set. The MUPPETS signal has a strong fluence dependence. With extrapolation to the low fluence limit, the ratio of cross sections for ground-to-exciton and exciton-to-biexciton absorption is found to be close to the predictions of the uncorrelated-electron model. The full two-dimensional MUPPETS data set is reported for the first time and is analyzed to detect heterogeneity in the exciton decay. The exciton has a substantial (>40%) nonradiative decay, but it is not due to a subset of defective particles. A surface relaxation in response to formation of the exciton is suggested. This data set is the first capable of detecting correlations between the biexciton and exciton decay mechanism. None is found.
CdSe/ZnS 核壳纳米粒子中激子和双激子的非辐射弛豫具有复杂的非指数动力学。本文从多群时瞬光谱（MUPPETS）提供了该系统的数据，MUPPETS 是一种二维动力学方法。之前的研究报道了分散的（非指数）双激子衰减[J. Am. Chem. Soc. 2013, 135, 1002]，在更严格的分析中得到了证实。额外的瞬态光栅数据允许对完整的复杂 MUPPETS 数据集进行定量处理。MUPPETS 信号对光强有很强的依赖性。通过对低光强极限的外推，发现基态到激子和激子到双激子吸收的截面比接近无关联电子模型的预测。首次报道了完整的二维 MUPPETS 数据集，并对其进行了分析，以检测激子衰减中的非均匀性。激子具有很大的（>40%）非辐射衰减，但这不是由于一部分有缺陷的粒子造成的。提出了一种表面弛豫的机制来解释激子的形成。该数据集是第一个能够检测双激子和激子衰变机制之间相关性的数据集。没有发现相关性。
