Au_xAg_y@ZrO₂ core-shell nanoparticles: synthesis, characterization, reactivity and optical limiting

Abstract

Au_xAg_y@ZrO₂ redispersible core-shell nanoparticles were prepared by a single step synthesis using the dimethyl formamide (DMF) reduction procedure. The material is stable for extended periods of time. The core-shell alloy nanoparticles were characterized by UV-vis spectroscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimetry and cyclic voltammetry. The as prepared particles are nanocrystalline in nature, but they give well-defined diffraction patterns upon heating to 100 °C for 8 h. The average diameter of the core is ~35 nm and typical shell thickness is 2-3 nm. The materials show interesting reactivity with halocarbons as in the case of naked metal nanoparticles, which vary with the composition of the alloy. Our experiments show that oxide-protected alloy nanoparticles are excellent optical limiters in the nanosecond regime. Optical nonlinearity of these systems has been investigated in detail and a qualitative model has been proposed. To the best of our knowledge, this is the first report of nanoparticles having a true alloy core and an oxide shell.