Room Temperature Space-selective Precipitation of Silver Nanoparticles inside Tb³+-doped Silica Xerogels using Femtosecond Laser

Space-selective precipitation of silver nanoparticles inside transparent paramagnetic silica xerogels doped with Tb 3+ and Ag + ions was performed at room temperature by a one-step irradiation process of a femtosecond laser without subsequent heat treatment.Paramagnetic silica xerogels doped with Tb 3+ ions were prepared via a sol-gel process using terbium nitrate with a drying process at temperature of 450 °C.The color change of the irradiated area and corresponding optical absorption peaks indicate the precipitation of Ag nanoparticles and localized surface plasmon resonance (LSPR) absorption.The Ag + ions were reduced and Ag atoms aggregated to form Ag nanoparticles, suggesting that the light energy incident on the irradiated xerogel was directly spent to aggregate Ag atoms.The positive correlation between pulse energy and particle size is different from that observed in the two-step method that includes a post-annealing step.X-ray photoelectron spectroscopy analysis showed that Ag ions were actually reduced by fs laser irradiation.A larger absolute value of Faraday rotation angle was observed in the femtosecond laser-irradiated region compared to the non-irradiated region.The enhanced Faraday rotation is observed particularly in the refractive index change region, and the laser processing technique using this xerogel material is expected to be applied to the fabrication of waveguide-type Faraday devices in the future.