Solvent and ligand effects on the optical properties of silver nanoparticles in silica sol−gel films J. A. García−Macedo 1* , V. M. Rentería−Tapia 1 , G. Valverde−Aguilar 1 1. Departamento de Estado Sólido. Instituto de Física, Universidad Nacional Autónoma de México. México D.F. C.P. 04510 * Contact author: Dr. Jorge Garcia Macedo Instituto de Física, UNAM Circuito de la Inv. Científica s/n C. P. 04510. Del. Coyoacán México, D.F. México. Tel. (5255) 5622−51−03 Fax (5255) 5616−15−35 E−mail: gamaj@fisica.unam.mx ABSTRACT Silver nanoparticles in sol−gel silica films have been synthesized by heat treatment in air atmosphere. We find that the surface plasmon resonance exhibits a principal peak at 534 nm, longer wavelength than that corresponding to the spherical silver nanoparticles in silica (400 nm). The anisotropy in the geometry of the metallic nanoparticles explains this noticeably red shift of the silver nanoparticles. The effect of solvents (ethanol, cyclohexane and toluene) and ligand (pyridine) on the optical properties of these nanoparticles are measured by UV−vis spectroscopy. The position of the surface plasmon resonance varies from 534 nm up to 573 nm depending on the refractive index or the concentration of the solvents. On the contrary, the surface plasmon resonance is gradually shifted to the blue from 534 nm up to 462 nm when the films were immersed in pyridine due to complexing on the surface of silver nanoparticles. These results show highest sensitivity of the surface plasmon to variations in the local environment of the nanoparticles and they suggest that the films can be used as colorimetric sensors. KEYWORDS: Silver nanoparticles, sol-gel, thin film, colorimetric sensor 1. INTRODUCTION A great effort has been done to prepare metallic nanoparticles of several sizes and shapes since they exhibit unusual optical, electronic, catalytic and magnetic properties in comparison to those of the bulk materials [1]. In particular, the linear optical properties of metallic nanoparticles have been extensively researched due to their potential in sensors and photonic applications [2−5]. The interesting colors that the metallic colloids exhibit are due to the surface plasmon resonance produced for collective oscillations of conduction electrons. Excitation of these electrons by an electromagnetic field causes scattering and absorption [6]. The resonance depends on the adsorbate−particle interaction, dielectric environment and morphology of the metallic nanoparticles. For example, the interaction of silver nanoparticles with organo−sulfur compounds causes a drastic red shift, broadening and damping of the surface plasmon [7]. Similarly, it has been reported the dependence of the surface plasmon resonance from non−spherical nanoparticles on the refractive index of the medium [8]. On the other hand, the Mie theory in the dipole approximation predicts color changes of Plasmonics: Metallic Nanostructures and Their Optical Properties VII, edited by Mark I. Stockman, Proc. of SPIE Vol. 7394, 73942T · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.826734 Proc. of SPIE Vol. 7394 73942T-1 Downloaded from SPIE Digital Library on 12 Oct 2009 to 132.248.209.119. Terms of Use: http://spiedl.org/terms