Background: Metal nanoparticles have been widely investigated due to their unique optical,
mechanical, and chemical properties compared with those of the same bulk material. These
properties can be tuned by controlling their size or shape, in this sense, several nanomaterials have
been obtained by means of both chemical and physical methods. For instance, silver nanoparticles
have been obtained in liquid media by using laser ablation or chemical reduction techniques. Another
way to obtain a colloidal silver nanoparticles is through the well-known pulsed laser irradiation
method which can produce a stable colloidal solution in a few minutes of irradiation and without
stabilizing molecules or ligands.
Methods: Silver nanopowder suspended in ethanol was irradiated with a pulsed laser at 532 nm via
optical fiber. Previously, the fiber was prepared by cleaving and removing its coating and then placed
in the middle of a cell. The pulse width was 15 ns and the pulse repetition frequency was 10 kHz.
Scanning and transmission electron microscopes were used to observe the silver nanoparticles before
and after laser irradiation, respectively. The samples were analyzed by means of UV-Vis spectrophotometer
to observe the absorption spectra.
Results: The absorption spectra show that particle size distribution increases according to the irradiation
time. The colloidal solution showed a color change (from gray to yellow) after having irradiated
it for 5 minutes. From TEM images, it can be observed that silver nanopowder was transformed to
semispherical particles with diameters smaller than 1μm, however, due to the wide particle size distribution
the colloidal solution was centrifuged for 30 min to separate the nanoparticles.
Conclusion: The pulsed laser irradiation method via optical fiber was successfully used to obtain a
stable yellow colloidal solution. Photomelting, photofusion, and photofragmentation are the responsible
phenomena for the change in morphology and size of the silver nanopowder.