CW and pulsed EPR study of silver nanoparticles in a SiO2 matrix

Metallic silver nanoparticles were prepared by the sol-gel method in an SiO 2 matrix. The process includes complexation of silicon alkoxides with metal salts, hydrolysis, polycondensation, formation of powder, and subsequent t hermal treatment first in oxidizing and second in reducing atmospheres. The sizes of metallic particles were determined both by X-ray diffraction and transmission electron microscopy. These measurements revealed sizes of meta llic particles between 1 and 20 nm, depending upon processing conditions. T he magnetic properties were investigated using electron paramagnetic resona nce spectroscopy in the temperature range between 4 and 300 K. The spin-lat tice relaxation time T-1 was measured by pulsed EPR. The temperature depend ence of T-1 is described by the relation 1/T-1 oc T-n, where 0.4 < n < 1. T his behavior is unusual and different from any well-known relaxation proces ses such as Raman, Direct or the Orbach-Aminov.