Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
Nanoscale. 2011 Sep 1;3(9):3849-59. doi: 10.1039/c1nr10544b. Epub 2011 Aug 8.
Both the excitation and emission processes of a fluorescent molecule positioned near a noble metal nanocrystal can interact strongly with the localized surface plasmon resonance of the metal nanocrystal. While the effects of this plasmon-fluorophore interaction on the intensity, polarization, and direction of the fluorescence emission have been intensively investigated, the plasmonic effect on the emission spectrum has barely been explored. We show, on the single-particle level, that the localized surface plasmon resonance of Au nanorods can strongly alter the spectral profile of the emission from adjacent fluorescent molecules. The fluorescent molecules are embedded in a mesostructured silica shell that is uniformly coated on each Au nanorod. The longitudinal plasmon resonance wavelengths of the nanorods are deliberately shifted away from the intrinsic fluorescence emission peak wavelength by synthetically tuning the nanorod aspect ratio. The resultant emission spectra of the fluorescent molecules are found to be remarkably modulated. Besides the intrinsic fluorescence peak, a plasmon-induced new peak emerges at the plasmon resonance wavelength. The intensity of this plasmon-induced fluorescence peak increases as the size of the Au nanorod is increased. This spectral modulation can be understood by depicting the decay process of the fluorophore with multiple vibrational energy levels. The plasmon with a specific resonance energy will enhance the transition rate between the energy levels that have the transition energy approximately equal to the plasmon energy. This plasmon-enhanced transition rate results in a modulated spectral profile of the fluorescence emission.
位于贵金属纳米晶附近的荧光分子的激发和发射过程均可与金属纳米晶的局域表面等离激元共振强烈相互作用。尽管已经深入研究了这种等离子体-荧光团相互作用对荧光发射强度、偏振和方向的影响，但对发射光谱的等离子体效应几乎没有探索。我们在单粒子水平上表明，金纳米棒的局域表面等离激元共振可以强烈改变相邻荧光分子的发射光谱轮廓。荧光分子嵌入在均匀涂覆在每个金纳米棒上的介孔二氧化硅壳中。通过合成调节纳米棒的纵横比，故意将纳米棒的纵向等离子体共振波长从荧光分子的固有荧光发射峰波长移开。发现荧光分子的发射光谱得到了显著的调制。除了固有荧光峰之外，在等离子体共振波长处出现了一个等离子体诱导的新峰。随着金纳米棒尺寸的增加，这个等离子体诱导的荧光峰的强度增加。通过描绘具有多个振动能级的荧光团的衰减过程，可以理解这种光谱调制。具有特定共振能量的等离子体将增强与等离子体能量近似相等的能量水平之间的跃迁速率。这种等离子体增强的跃迁速率导致荧光发射的光谱轮廓调制。
