Uematsu Takafumi, Maenosono Shinya, Yamaguchi Yukio
Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.
J Phys Chem B. 2005 May 12;109(18):8613-8. doi: 10.1021/jp050328k.
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.
利用不同强度和波长的激发光，研究了玻璃基底上CdSe/ZnS核壳量子点（QD）单层和多层膜中的光致荧光增强（PFE）行为。采用胶体化学合成法制备了用三正辛基氧化膦（TOPO）包覆的CdSe/ZnS量子点，并通过旋涂在玻璃基底上制备了单层和多层量子点膜。在干燥氮气气氛中连续照射可大大提高量子点单层的荧光量子产率（QY），而量子点多层膜的QY或荧光强度衰减则有较小增强。此外，激发波长越短，PFE越明显。在任何波长下，QY的增加速率都随着激发强度的降低而增加。在单层和多层膜中均观察到了这些依赖性。我们的结果表明，电子向基底的光发射是PFE的起源。假设基底中捕获的电子的充电效应，提出了一个唯象模型来解释所有实验结果，即对激发光强度和波长的依赖性以及单层和多层膜之间PFE行为的定性差异。
