Gold nanoparticles absorption efficiency

Farrer, R.A., Butterfield, F.L., Chen, V.W. and Fourkas, J.T. (2005) Highly efficient multiphoton-absorption-induced luminescence from gold nanoparticles. Nano Letters, 5, 1139-1142. 

In the experiments, fluorescence signals cannot only be enhanced by GNPs but can also be absorbed. Therefore, the absorption efficiency of GNPs was considered in this study. As an example. Figure 8.13 shows the absorption efficiency of plane waves by a gold spherical nanoparticle with diameter of 20 nm in water ( .=1.33) as a function of illuminating wavelength. 

Figure 10 shows the absorption spectrum of the gold particles in solution (dashed curve) and the fluorescence spectrum of a solution of lissamine fluorophores both before and after they are attached to the gold particles. As expected, the gold particles in solution show an absorption peak centered at the dipolar plasmon frequency. It is seen that the fluorescence of the lissamine is strongly quenched by presence of the gold nanoparticles. It was estimated that the quenching efficiency exceeded 99%, when the residual fluorescence of unbound fluorophores was taken into account. 

Lissamine molecules in the vicinity of gold nanoparticles because the [H oportionality of Einstein coefficients of absorption and emissiai must hold as long as absorption and emission occur without a Stokes shift. We find that the absorption cross section is changed by 30% for nanoparticles of 30 nm radius. This effect is ready included in the fluorescence quenching efficiency above and will be included in a similar way in the analysis of the following time resolved measurements. 

Electron injection dynamics in the conduction band of metal oxide materials from dye molecules or metal nanoparticles, which is important when applied to sensitized solar cells, can be monitored in the infrared by 100 fs time resolution. In this chapter, technical details of femtosecond visible-pump/IR-probe transient absorption spectroscopy and some typical spectroscopic data revealing the mechanism of electron injection process were described. A great advantage of this technique is that one can observe transient absorption of injected electrons easily because of the intense intraband transition of an electron at the bottom of or at the trap level just below the conduction band of the metal oxide that forms an electrode. In the case of dye-sensitized solar cells, the effects of metal oxide, dye, solvent and additive ions on the rate and efficiency of electron injection were discussed in detail. One recent discovery, plasmon-induced electron injection from a gold nanoparticle to a Ti02 nanoparticle, was presented to show how femtosecond visible-pump/IR-probe transient absorption spectroscopy is useful in studying this kind of new charge transfer dynamics in a nano-structured system. 

Figure 5.58 (a) Schematic illustration of the binding in a Au-dithiol-CdS-dithiol-CdS multilayer, where the CdS nanoparticles are formed from reversed micelles onto a modified gold surface, (b) Action spectra of composite films and absorption spectra of the CdS nanoparticle dispersion before being immobilized continuous and dashed lines show the action spectra on different scales and represent the relative photocurrent efficiencies of Au-dithiol-CdS and Au-dithiol-CdS-dithiol-CdS, respectively. Reprinted with permission from O. Nakanishi, B. Ohtani and K. Uoskai, /. Phys. Chem., B, 102, 1571 (1998). Copyright (1998) American Chemical Society... 

Arabinogalactan is transparent both in UV and visible ranges, and electronic absorption spectroscopy can be successfully used to study arabinogalactan assisted nanoparticles. The absorption spectra of the silver and gold nanocomposites solutions have intensive absorption peaks at 420 and 524 nm, respectively (Fig. la), which proves the presence of silver and gold zero-valence metals [3]. The peaks are attributed to collective excitations of conduction electrons (plasmonic resonance). This fact is of interest for synthesis of water soluble highly efficient non-linear optical materials [1]. 

Chemical vapor deposition (CVD) has been used to prepare nanoparticle catalysts, although the technology is quite expensive. Dimethylgold acetylacetonate absorbs on supports such as MgO. Decomposition at > 100°C produces an efficient CO oxidation catalyst. X-ray absorption near edge (XANES) and extended X-ray absorption fine structure spectroscopies (EXAFS) showed that, under steady-state CO oxidation conditions, the catalyst contained Au(0) in the form of (on average) Aus clusters and also additional gold as... 

Metallic nanoparticles, usually made of gold or silver, scatter light with remarkable efficiency by surface plamsonic resonance effect. Typical scattering cross sections of metal nanoparticles greatly exceed the absorption cross-section of fluorescent dyes [40] and of fluorescent proteins [41]. The photostability, water... 

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