Absorption plasmon

Link S and El-Sayed M A 1999 Size and temperature dependence of the plasmon absorption of colloidal gold nanoparticles J. Phys. Chem. B 103 4212... 

Michaelis and Henglein [131] prepared Pd-core/Ag-shell bimetallic nanoparticles by the successive reduction of Ag ions on the surface of Pd nanoparticles (mean radius 4.6 nm) with formaldehyde. The core/shell nanoparticles, however, became larger and deviated from spherical with an increase in the shell thickness. The Pd/Ag bimetallic nanoparticles had a surface plasmon absorption band close to 380 nm when more than 10-atomic layer of Ag are deposited. When the shell thickness is less than 10-atomic layer, the absorption band is located at shorter wavelengths and the band disappears below about three-atomic layer. 

UV-visible spectra of the Au-acetone sols showed absorptions at 706 and 572 nm, the latter being attributed to plasmon absorption.(54) We have found that the plazmon absorption was not a good indicator of true particle size (obtained by TEM) since the 572 band did not shift significantly with particle size. ( 35) However, in aqueous solution this band has been used successfully to roughly determine particle size.(55)... 

Fig. 1.12 (A) Increase in surface plasmon ab- and from mixtures with lower chitosan concen-sorptionasAu nanoparticles are produced from a tration (ii) or lower HAuCI4 amount (iii) six reaction mixture containing 1 % chitosan, 1 % different self-sustained nanocomposite films acetic acid and 0.01 % tetrachloroauric (III) acid showing the control over the optical properties. (HAuCU) (B) shiftofsurface plasmon absorption Reprinted with permission from [164], 2004, for films prepared from the previous mixture (i), American Chemical Society.

Figure 21.6 Schematic illustration of the dynamics of the photoluminescence from the Au(0) i system. The inset shows the comparison of the Au(0) i surface plasmon absorption peak with the spectral distribution of the Au(0) i emission peakfor excitation at 3.14 eV (395 nm).

In a more simple and cheap way, silver clusters can be prepared in aqueous solutions of commercially available polyelectrolytes, such as poly(methacrylic acid) (PM A A) by photo activation using visible light [20] or UV light [29]. Ras et al. found that photoactivation with visible light results in fluorescent silver cluster solutions without any noticeable silver nanoparticle impurities, as seen in electron microscopy and from the absence of plasmon absorption bands near 400 nm (F = 5-6%). It was seen that using PMAA in its acidic form, different ratios Ag+ MAA (0.15 1-3 1) lead to different emission bands, as discussed in the next section (Fig. 12) [20]. When solutions of PMAA in its sodium form and silver salt were reduced with UV light (365 nm, 8 W), silver nanoclusters were obtained with emission band centered at 620 nm and [Pg.322]

Adsorption of ions or molecules on metal clusters markedly affects their optical properties. It was shown that the intensity and the shape of the surface plasmon absorption band of silver nanometric particles, which is close to 380 nm, change upon adsorption of various substances [125]. The important damping of the band generally observed is assigned to the change of the electron density of the thin surface layer of the... 

Irradiation with 7-rays was also used to synthesize bimetallic nanoparticles. Remita et al. synthesized poly(vinyl alcohol) (PVA)-stabilized Ag/Pt bimetallic nanoparticles by radiolysis of an aqueous mixture of Ag2S04 and K2PtCl4 at a concentration of 10-4 mol dm-3. A typical Ag plasmon absorption band is observed at —410 nm with only low intensity at the mole ratio of Ag Pt = 60 40, indicating the formation of Ag/Pt bimetallic nanoparticles. Polyfacrylic acid) was also used as the stabilizer, although the resulting UV-Vis spectra were quite different. 

Plasmon absorption of dispersions of coin metal fine particles like gold was often used to estimate the size of particles. The absorption peak can be calculated on the basis of Mie theory. However, this is not always true. The peak position can move, depending on not only the size of the particles but also the environment of the particles and the extent of aggregation of the particles. Thus, UV-Vis absorption is only used just for understanding the rough image of particle dispersions. 

Differences in surface plasmon absorption among various metals are clearly revealed by imagining the trajectories to be superposed onto the contour plot . Spherical silver and aluminum particles have intense surface plasmon absorption peaks because t" is small at the frequency where c is - 2, whereas gold... 

Surface plasmon absorption has been observed for small particles of several other metals, and many calculations have been published these are too... 

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