Itoh Tamitake, Kikkawa Yasuo, Biju Vasudevanpillai, Ishikawa Mitsuru, Ikehata Akifumi, Ozaki Yukihiro
Nano-Bioanalysis Team, Health Technology Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 2217-14 Hayashi-cho, Takamatsu Kagawa 761-0395, Japan.
J Phys Chem B. 2006 Nov 2;110(43):21536-44. doi: 10.1021/jp064070p.
We observed a background luminescence emission that was associated with surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G (R6G) molecules adsorbed on single Ag nanoaggregates and investigated the origin of the background luminescence. Thanks to the observation of single nanoaggregates, we clearly identified nanoaggregate-by-nanoaggregate variations in the steady-state and time-resolved background luminescence spectra of each nanoaggregate. From the variations in the steady-state spectra, two kinds of key properties were revealed. First, the background luminescence spectra were divided into four components: one fluorescence band corresponding to the monomers of R6G and three Lorentzian bands whose maxima were red-shifted from the fluorescence maximum of the monomer by several tens of nanometers. On the basis of the red-shifted luminescence maxima, and experimental and theoretical studies of background luminescence, we attributed the three background luminescences to fluorescence from aggregates (dimer and two kinds of higher-order aggregates) of R6G molecules on an Ag surface. Second, a positive correlation was observed between wavelengths of background luminescence maxima and wavelengths of plasmon resonance maxima. This positive correlation invoked the idea that the dipoles of both the background luminescence and the plasmon radiation are coupled with each other. From the key observations in the steady-state background luminescence spectra, we propose that two factors contribute to the variations in the steady-state background luminescence spectra; one is the aggregation (monomer, dimer, and two kinds of higher-order aggregates) of R6G molecules on an Ag surface, and the other is plasmon resonance maxima of single Ag nanoaggregates. Considering these two factors, we propose that the variations in the time-resolved background luminescence spectra are associated with deaggregation of R6G molecules (higher- to lower-order aggregates) and temporal shifts in the plasmon resonance maxima of single Ag nanoaggregates.
我们观察到一种背景发光发射，它与吸附在单个银纳米聚集体上的罗丹明6G（R6G）分子的表面增强共振拉曼散射（SERRS）相关，并研究了背景发光的起源。由于对单个纳米聚集体的观察，我们清楚地识别出每个纳米聚集体的稳态和时间分辨背景发光光谱中纳米聚集体之间的差异。从稳态光谱的差异中，揭示了两种关键特性。首先，背景发光光谱分为四个成分：一个对应于R6G单体的荧光带和三个洛伦兹带，其最大值从单体的荧光最大值红移了几十纳米。基于红移的发光最大值以及背景发光的实验和理论研究，我们将这三种背景发光归因于银表面上R6G分子聚集体（二聚体和两种高阶聚集体）的荧光。其次，观察到背景发光最大值的波长与等离子体共振最大值的波长之间存在正相关。这种正相关引发了这样一种观点，即背景发光和等离子体辐射的偶极子相互耦合。从稳态背景发光光谱的关键观察结果来看，我们提出有两个因素导致稳态背景发光光谱的变化；一个是银表面上R6G分子的聚集（单体、二聚体和两种高阶聚集体），另一个是单个银纳米聚集体的等离子体共振最大值。考虑到这两个因素，我们提出时间分辨背景发光光谱的变化与R6G分子的解聚（从高阶到低阶聚集体）以及单个银纳米聚集体的等离子体共振最大值的时间偏移有关。
