Silver Nanoparticles with Broad Multiband Linear Optical Absorption
Silver Nanoparticles with Broad Multiband Linear Optical Absorption
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DOI：
10.1002/anie.200900298
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发表时间：
2009-01-01
影响因子：
16.6
通讯作者：
Stellacci, Francesco
中科院分区：
文献类型：
--
作者：
Bakr, Osman M.;Amendola, Vincenzo;Stellacci, Francesco
金属纳米粒子（NPs）的光学和电子特性使其成为许多领域的理想应用，如生物科学，[1-3]纳米光子学[4]和纳米电子学。[5，6]银纳米颗粒吸引了大量的研究工作，因为它们的性质强烈依赖于颗粒尺寸，[7-9]形状，[10，11]周围介质，[12]和聚集状态。[11]小的银团簇（最多约8个原子）具有类似分子的光学跃迁，其吸收带取决于组成团簇的原子的数量，并且具有明亮的荧光发射。[13最多21个原子的簇表现出一个或多个光吸收最大值。[15]随着粒子的增长（大小！2 nm）时，它们会失去这些特性，并形成一个依赖于其自由电子的表面等离子体共振的光吸收带-粒子越大，共振越强。[8，16] jeldom模型[7]和含时密度泛函理论计算[17]已被用于解释分子状态，而经典电磁理论和方法，如米氏理论，已被证明足以模拟较大粒子的光学性质。[9，18]在此，我们表明，可以产生芳基硫醇涂覆的银NP，其在中等尺寸下显示出强烈和广泛的非等离子体光学性质。这些颗粒有八个不同的吸收带，覆盖整个可见光谱，消光截面高达2.59 - 105 L molecular-1 cm-1。它们相对稳定，并且在加热时生长成具有等离子体样吸收的较大NP。这些颗粒具有主要的尺寸（dcore% 1.3 nm）和在其光谱中的高度限定的结构。量子限制芳基硫醇银簇结构的从头计算再现所观察到的光谱的复杂性，并指出所观察到的过渡的显着的分子性质。这些强吸收和宽吸收纳米颗粒（IBAN）具有比常规有机染料和无机QD更大的横截面，并且覆盖更宽的波长范围（它们的吸收带覆盖380-850 nm的范围）。最近，一些研究小组报道了小的（2 nm）金纳米颗粒的结构测定。[19-22]这些远大于上述簇的NP显示出它们的核心金属原子和它们的芳基硫醇配体的独特结构。[19-22]除了它们独特的结构基序之外，这些金颗粒中的一些在它们的吸收光谱中表现出分子阶跃。[19用其他硫醇[25-28]包覆的类似尺寸的颗粒，其结构尚未确定，也在其线性光谱中显示出这些阶梯状跃迁。然而，随着簇的尺寸增大或变得不那么单分散，台阶状行为变得不那么清晰。[29-31]关于银NP（尺寸< 2 nm）的几篇报道显示出非常宽的阶跃式光学跃迁，即使在吸收光谱的一阶导数中也难以辨别其特征。[32本文报道的颗粒（IBAN）是第一个显示出强的和复杂的分子状吸收峰的银纳米颗粒，其与先前报道的银簇或银NP的吸收峰显著不同，即使当它们是纳米颗粒时也是如此。
The optical and electronic properties of metal nanoparticles (NPs) have made them ideal for applications in many fields such as bioscience,[1–3] nanophotonics,[4] and nanoelectronics.[5, 6] Silver NPs have attracted large research efforts as their properties strongly depend on the particles size,[7–9] shape,[10, 11] surrounding medium,[12] and aggregation state.[11] It is accepted that small silver clusters (up to about 8 atoms) have molecule-like optical transitions with absorption bands that depend on the number of atoms that compose the cluster and with a bright fluorescence emission.[13, 14] Clusters of up to 21 atoms exhibit one or more photoabsorption maxima.[15] As particles grow (size! 2 nm), they lose these properties and develop an optical absorption band that depends on the surface plasmon resonance of their free electrons—the larger the particles the stronger the resonance.[8, 16] The jellium model [7] and time-dependent density functional theory calculations [17] have been used to explain the molecule-like state, whereas classical electromagnetic theories and methods, such as Mie theory, have been proven to be adequate in modeling the optical properties of larger particles.[9, 18] Herein we show that it is possible to create aryl thiol coated silver NPs that show intense and broad non-plasmonic optical properties at an intermediate size. These particles have eight distinct absorption bands covering the entire visible spectrum with extinction cross-sections as high as 2.59 105 L molÀ1 cmÀ1. They are relatively stable and upon heating grow into larger NPs with plasmon-like absorption. These particles have a predominant size (dcore% 1.3 nm) and a highly defined structure in their optical spectra. Abinitio calculations for a quantum confined aryl thiolate silver cluster structure reproduce the complexity of the spectra observed and point to a significant molecular nature of the observed transitions. These intensely and broadly absorbing nanoparticles (IBANs) have larger cross-sections than conventional organic dyes and inorganic QDs, and cover a broader range of wavelengths (their absorption bands cover the range 380–850 nm). These properties make IBANs ideal candidates for light-harvesting applications.Recently, a few groups reported the structure determination of small (2 nm) gold NPs.[19–22] These NPs, which are far larger than the clusters mentioned above, show a unique structure of both their core metallic atoms and of their aryl thiol ligands.[19–22] In addition to their unique structural motif, some of these gold particles exhibit molecular steplike transitions in their absorption spectra.[19, 22–27] Similarly sized particles coated with other thiols,[25–28] whose structures have not yet been determined, also show these steplike transitions in their linear optical spectra. However, the steplike behavior becomes less resolved as the clusters grow in size or become less monodisperse.[29–31] A couple of reports on silver NPs (size< 2 nm) have shown very broad steplike optical transitions, whose characteristics are hard to discern even in the first derivative of the absorption spectra.[32, 33] The particles reported herein (IBANs) are the first silver nanoparticles to show strong and complex molecular-like absorption peaks that are markedly different from those previously reported for either silver clusters or silver NPs, even when they are