Temperature Dependence of F?rster Thermalization and Population Decay in PbSe Nanocrystals

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• 作者：Rafael Quintero-Torres ; Frank C. J. M. van Veggel ; Jeff F. Young
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 16, 2014
• 年：2014
• 卷：118
• 期：2
• 页码：1377-1385
• 全文大小：482K
• ISSN：1932-7455

文摘

Time-resolved photoluminescence spectroscopy is used to quantify the F枚rster-mediated exciton migration rate and the exciton population decay rate in drop-cast solid emulsions of PbSe colloidal nanocrystals emitting near 1.5 渭m from 77 to 300 K. For both unimodal and bimodal emulsions, at a fixed temperature in a given sample the measured time constants that characterize the fast transient decay (blue side of the spectrum) and buildup (red side of the spectrum) vary considerably with emission wavelength, but the average fast time constant, 25 ns, varies little (i.e., within <25%) with temperature from 77 to 300 K. Over the same temperature range, the exciton population lifetime, ascribed to nonradiative decay, decreases by 5 times but is always longer than the F枚rster time constant. The increase of the F枚rster-mediated efficacy of exciton redistribution at low temperatures before they decay is therefore almost all due to the variation of the nonradiative decay rate. By analyzing the temporally resolved and steady-state emission spectra, it is noted that the time required for the exciton population to equilibrate is nonexponential and considerably longer (150 ns) than the rapid decay and buildup time constants extracted from the decay curves at fixed wavelengths.