US Naval Research Laboratory, Division of Optical Sciences, Washington, DC 20375, USA.
Small. 2011 Jul 18;7(14):2101-8. doi: 10.1002/smll.201100802. Epub 2011 Jun 28.
In this report the correlation between the solution photoluminescence (PL) quantum yield and the fluorescence emission of individual semiconductor quantum dots (QDs) is investigated. This is done by taking advantage of previously reported enhancement in the macroscopic quantum yield of water-soluble QDs capped with dihydrolipoic acid (DHLA) when self-assembled with polyhistidine-appended proteins, and by using fluorescence coincidence analysis (FCA) to detect the presence of "bright" and "dark" single QDs in solution. This allows for changes in the fraction of the two QD species to be tracked as the PL yield of the solution is progressively altered. The results clearly indicate that in a dispersion of luminescent nanocrystals, "bright" (intermittently emitting) single QDs coexist with "permanently dark" (non-emitting) QDs. Furthermore, the increase in the fraction of emitting QDs accompanies the increase in the PL quantum yield of the solution. These findings support the idea that a dispersion of QDs consists of two optically distinct populations of nanocrystals--one is "bright" while the other is "dark;" and that the relative fraction of these two populations defines the overall PL yield.
在本报告中，我们研究了溶液光致发光（PL）量子产率与单个半导体量子点（QD）荧光发射之间的相关性。这是通过利用先前报道的二氢硫辛酸（DHLA）封端的水溶性 QD 在与多组氨酸缀合的蛋白质自组装时宏观量子产率的增强，以及利用荧光符合分析（FCA）来检测溶液中“亮”和“暗”单个 QD 的存在来实现的。这允许随着溶液的 PL 产率逐渐改变，跟踪两种 QD 物种分数的变化。结果清楚地表明，在发光纳米晶体的分散体中，“亮”（间歇性发射）单个 QD 与“永久暗”（非发射）QD 共存。此外，发射 QD 的分数增加伴随着溶液 PL 量子产率的增加。这些发现支持这样一种观点，即 QD 的分散体由两种具有不同光学性质的纳米晶体组成——一种是“亮”的，另一种是“暗”的；这两种群体的相对分数定义了整体 PL 产率。
