Tuning the structural and optical properties of gold/silver nano-alloys prepared by laser ablation in liquids for optical limiting, ultra-sensitive spectroscopy, and optical trapping

The plasmon resonance of metallic Au/Ag nano-alloys in the colloidal state was tuned from 400 nm to 500 nm using a laser irradiated technique performed directly in the liquid state. Interesting optical nonlinearities, trapping effects and spectroscopic enhancements were detected by modifying the gold molar fraction in the nano-alloys. In particular a reduction of the limiting threshold was observed by increasing the gold amount. The SERS activity of the Au/Ag alloys was tested in liquid and in solid state in presence of linear carbon chains as probe molecules. The increased Raman signals for nanoparticles with different Au/Ag atomic ratio are presented. Finally, studies and prospects for optical and Raman tweezers experiments are discussed. -- Highlights: ► Synthesis of contaminant-free Au–Ag composite nanocolloids by PLA. ► Reduction of optical limiting threshold by increasing the Au content. ► SERS activity on the Au/Ag nanoalloys probed with LCCs. ► SERS optical trapping of individual nanoalloy-LCCs nanoaggregates.