Temperature-Dependent Absorption and Ultrafast Luminescence Dynamics of Bi-Icosahedral Au25 Clusters

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• 作者：Mary Sajini Devadas ; Viraj Dhanushka Thanthirige ; Semere Bairu ; Ekkehard Sinn ; Guda Ramakrishna
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：November 7, 2013
• 年：2013
• 卷：117
• 期：44
• 页码：23155-23161
• 全文大小：409K
• 年卷期：v.117,no.44(November 7, 2013)
• ISSN：1932-7455

文摘

Temperature-dependent absorption and ultrafast luminescence dynamics of [Au₂₅(PPh₃)₁₀(SC₆)₅Cl₂ ]²⁺ (Au₂₅-rod) was studied and compared with [Au₂₅(SC₆)₁₈]^{鈭?/sup> (Au₂₅-sphere) and Au₃₈(SC₂Ph)₂₄ (Au₃₈-rod) to understand the influence of the crystal structure on the optical properties of monolayer protected gold clusters. The temperature-dependent absorption of Au₂₅-rod shows a shift in the absorption maximum to high energies and a small increase in the oscillator strength with decrease in temperature. The energy shift was modeled via the O鈥橠onnell and Chen relationship, which yielded average phonon energy of 160 卤 80 cm鈥?, quite smaller than the 350 cm鈥? observed for Au₂₅-sphere and Au₃₈-rod. There is an increase in the oscillator strength with a decrease in temperature of about 40% for Au₂₅-rod while it is nearly 250% for Au₂₅-sphere and more than 180% for Au₃₈-rod. The oscillator strength increase is attributed to the coupling of core-gold exciton and shell-gold phonons. The smaller increase in the oscillator strength for Au₂₅-rod is consistent with its structure that possesses no shell-gold. Femtosecond luminescence measurements carried out on Au₂₅-rod clusters show wavelength-independent ultrafast luminescence decay traces. The lifetimes from the analysis are consistent with the relaxation of higher energy states. In contrast, Au₂₅-sphere and Au₃₈-rod clusters show specific wavelength-dependent luminescence growth and decay, representing the relaxation of core-gold states to shell-gold states.}