Browsing by Subject "Spectral shifts"

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Open Access
Charge storage and release onto Au and Ag nanoparticles in aqueous medium as probed by optical spectroscopy
(Cognizure, 2014) Tunc, I.; Sezen, H.; Guvenc, H. O.; Süzer, Şefik
Gold and silver nanoparticles in aqueous solutions can store negative or positive charges when, respectively, NaBH4, KI are introduced into the same media. The charge storage can be followed by the spectral shifts in the corresponding surface plasmon resonance (SPR) bands of these nanoparticles. In a similar way, the kinetics of these two processes can be monitored by the same shifts. Accordingly, we show that although Au nanoparticles exhibit smaller spectral shifts upon both negative and positive charge storage, when compared with Ag nanoparticles, their kinetics are faster towards reduction (electron storage) and comparable towards oxidation. Hence, if not the spectral shifts, the kinetics of the electron storage process can be correlated to the larger electron affinity of Au nanoparticles, when compared with those of Ag. The similarity of the kinetics towards oxidation must also be related to the small difference between the ionization potentials of Au and Ag nanoparticles.
Open Access
Optical response of Ag-Au bimetallic nanoparticles to electron storage in aqueous medium
(2008) Tunc, I.; Guvenc, H. O.; Sezen, H.; Süzer, Şefik; Correa-Duarte, M. A.; Liz-Marzán, L. M.
Composition and structure dependence of the shift in the position of the surface plasmon resonance band upon introduction of NaBH 4 to aqueous solutions of gold and silver nanoparticles are presented. Silver and gold nanoalloys in different compositions were prepared by co-reduction of the corresponding salt mixtures using sodium citrate as the reducing agent. After addition of NaBH 4 to the resultant nanoalloys, the maximum of their surface plasmon resonance band, ranging between that of pure silver (ca. 400 nm) and of pure gold (ca. 530 nm), is blue-shifted as a result of electron storage on the particles. The extent of this blue shift increases non-linearly with the mole fraction of silver in the nanoparticle, parallel to the trends reported previously for both the frequency and the extinction coefficient of the plasmon band shifts. Gold(core)@silver(shell) nanoparticles were prepared by sequential reduction of gold and silver, where addition of NaBH 4 results in relatively large spectral shift in the plasmon resonance band when compared with the nanoalloys having a similar overall composition. The origin of the large plasmon band shift in the core-shell is related with a higher silver surface concentration on these particles. Hence, the chemical nature of the nanoparticle emerges as the dominating factor contributing to the extent of the spectral shift as a result of electron storage in bimetallic systems. Copyright © 2008 American Scientific Publishers All rights reserved.