Pei Huan, Zhao Jiaxin, Peng Weifeng, Dai Qiyuan, Wei Yong
School of Information Science and Engineering, Yanshan University, Qinhuangdao, 066004, People's Republic of China.
Key Laboratory for Microstructural Material Physics of Hebei Province, School of Science, Yanshan University, Qinhuangdao, 066004, People's Republic of China.
Nanotechnology. 2023 Oct 13;35(1). doi: 10.1088/1361-6528/acfe15.
We present a theoretical analysis of plasmon-enhanced fluorescence (PEF) and Raman scattering (PERS) spectroscopy of a single molecule confined in the laser-irradiated metallic nanoparticles (NPs) dimer, focusing on the origin of the spectral enhancement and quenching effects. The theoretical method of-parameters has been used to calculate the dimer distance-dependent nonlocal dielectric effect in Ag and Au NPs. Meanwhile, other damping rates and electric field enhancements are quantitatively computed by finite element method. Moreover, PEF and PERS spectra of rhodamine 6G are obtained within the density-functional theory. Our calculated results show that the PERS mainly depend on the excitation and emission field enhancements, and thus it occurs at the narrower dimer gap due to the stronger localized plasmon coupling. The PEF is related to fluorescence rate caused by the competition between excitation electric field and quantum efficiency, and the increase of former may enhance the fluorescence intensity while the lower latter lead to reduce the intensity as decreasing the dimer distance. The contribution of nonlocal dielectric effect can significantly reduce the quantum efficiency at smaller distance so that it overcomes the excitation field enhancement, leading to the fluorescence quenching for Au NPs dimer. Furthermore, by optimizing the dimer distance and NPs size, the maximum PERS and PEF cross sections reach 10and 10under 2.45 eV laser excitation for Ag NPs dimer, and 10for Au NPs. Our study finely explains the experiment results showed either fluorescence enhancement or quenching with the change of molecule-NPs distance, and better guidance for optimizing the experiments.
我们对限制在激光辐照金属纳米颗粒（NP）二聚体中的单分子的表面等离子体激元增强荧光（PEF）和拉曼散射（PERS）光谱进行了理论分析，重点关注光谱增强和猝灭效应的起源。采用参数理论方法计算了银和金纳米颗粒中与二聚体距离相关的非局部介电效应。同时，通过有限元方法定量计算了其他阻尼率和电场增强。此外，在密度泛函理论范围内获得了罗丹明6G的PEF和PERS光谱。我们的计算结果表明，PERS主要取决于激发和发射场增强，因此由于更强的局域表面等离子体耦合，它发生在更窄的二聚体间隙处。PEF与激发电场和量子效率之间竞争引起的荧光速率有关，前者的增加可能会增强荧光强度，而后者的降低会导致随着二聚体距离减小而降低强度。非局部介电效应的贡献在较小距离下可显著降低量子效率，从而克服激发场增强，导致金纳米颗粒二聚体的荧光猝灭。此外，通过优化二聚体距离和纳米颗粒尺寸，在2.45 eV激光激发下，银纳米颗粒二聚体的最大PERS和PEF截面分别达到10和10，金纳米颗粒的最大PERS截面达到10。我们的研究很好地解释了随着分子 - 纳米颗粒距离变化而出现的荧光增强或猝灭的实验结果，并为优化实验提供了更好的指导。
