Photoinduced fluorescence enhancement in mono- and multilayer films of CdSe/ZnS quantum dots: Dependence on intensity and wavelength of excitation light
Photoinduced fluorescence enhancement in mono- and multilayer films of CdSe/ZnS quantum dots: Dependence on intensity and wavelength of excitation light
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DOI：
10.1021/jp050328k
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发表时间：
2005-05-12
影响因子：
3.3
通讯作者：
Yamaguchi, Y
中科院分区：
文献类型：
--
作者：
Uematsu, T;Maenosono, S;Yamaguchi, Y
用不同强度和波长的激发光研究了玻璃衬底上的单层和多层膜中的光诱导荧光增强(PFE)行为。采用胶体化学合成法制备了三正辛基氧化膦(TOPO)包覆的CdSe/ZnS量子点，并用旋涂法制备了单层和多层量子点薄膜。在干燥的氮气气氛中，QD单层的荧光量子产率(QY)显著提高，而QD多层膜的QY略有增加或荧光强度衰减。此外，激发波长越短，PFE越明显。在任意波长下，QY的增加速率随激发强度的降低而增大。在单层和多层膜中都观察到了这些依赖关系。我们的结果表明，电子向衬底的光喷射是PFE的起源。假设电子在衬底中的电荷效应，提出了一个唯象模型来解释所有的实验结果，即对激发光强度和波长的依赖以及单层和多层膜在PFE行为上的定性差异。
Photoinduced fluorescence enhancement (PFE) behavior in mono- and multilayer films of CdSe/ZnS core/shell quantum dots (QDs) on glass substrates was investigated using various intensities and wavelengths of excitation light. CdSe/ZnS QDs capped with tri-n-octylphosphine oxide (TOPO) were produced using colloidal chemical synthesis, and mono- and multilayer QD films were fabricated on glass substrates by spin coating. The fluorescence quantum yield (QY) of the QD monolayer was greatly enhanced by continuous irradiation in a dry nitrogen atmosphere, whereas the QD multilayer showed a small enhancement of the QY or fluorescence intensity decay. In addition, the shorter the excitation wavelength, the more pronounced the PFE. The rate of increase of the QY increased with decreasing excitation intensities at any wavelength. These dependences were observed in both mono- and multilayer films. Our results suggest that the photoejection of electrons to the substrate is the origin of PFE. Assuming the charging effect of electrons trapped in the substrate, a phenomenological model is proposed to explain all of the experimental results, that is, the dependence on the intensity and wavelength of excitation light and the qualitative difference in PFE behavior between mono- and multilayer films.