Optical limiting of gold nanoparticle aggregates induced by electrolytes.

The electronic absorption spectra and optical-limiting (OL) properties of gold nanoparticle (AuNP) aggregates induced by KCl and NaCl have been investigated using 4.1-ns laser pulses at 532 nm. Although the individual AuNP colloid shows no optical-limiting effect, the AuNP aggregates exhibit significant optical-limiting characteristics. With an increased concentration of KCl and NaCl, the surface plasmon resonance (SPR) band shifts to a longer wavelength, and the optical-limiting performance is enhanced. Both the electronic absorption and optical limiting are influenced by the particle size. The larger the individual nanoparticle, the further red-shifted the SPR band and the stronger the optical limiting. Optical limiting of aggregates induced by KCl is stronger than that of aggregates induced by NaCl. Mechanistic studies reveal that free-carrier absorption is the dominant contributor to the optical limiting, with negligible contribution from nonlinear scattering.