Color modulation of Ag nanoparticle dispersion by light-induced aggregation^†

In this paper, it is demonstrated that aggregation of Ag nanoparticles dispersed in pure water is mediated by strong dipole–dipole interactions produced by light irradiation. Expecting the effect of attractive forces caused by the dipole moments arising from localized surface plasmon resonance, an irradiation source based on the spectrum of the scattering cross section calculated from the geometric characteristics and dielectric constants of Ag and pure water is employed. In this process, it is possible to modulate the optical color of the dispersion by controlling the degree of aggregation of particles using the irradiation time without a chemical reaction.