SPECTRAL DEPENDENCE OF SELECTIVE PHOTOMODIFICATION IN FRACTAL AGGREGATES OF COLLOIDAL PARTICLES

Localization of optical excitations and selective photomodification ar e studied experimentally in fractal aggregates of silver colloidal nan oparticles. The localized optical excitations of the fractal colloids cover a broad spectral range, from the visible to the infrared. We sho w that the absorbed laser energy is localized In an increasingly small er number of particles with increasing the laser wavelength from 355 t o 1900 nm. The size of the photomodified regions can be as small as 20 nm. The observed modification is explained by optically induced sinte ring (coalescence) of colloidal nanoparticles. [S0031-9007(97)05209-5] .