Laser-induced silver nanocrystal formation in polyvinylpyrrolidone solutions

We report unusual laser-induced shape conversions of silver nanoparticles dispersed in polyvinylpyrrolidone (PVP) aqueous solutions. Silver nanocrystals such as nanoplates and nanorods were formed using laser irradiation for colloidal silver nanoparticles prepared using laser ablation in aqueous solutions of PVP. Differing from the nanocrystal formation observed in neat water and halide solutions, which were induced by weak laser or fluorescent-light irradiation, the nanocrystal formation in PVP solutions was induced by strong laser irradiation. On the other hand, nanocrystal formation was not observed in polyvinylalcohol (PVA) solutions, in which fusion of nanoparticles were prominent. It is proposed that the nanocrystals were formed from fragmented nanoparticles protected by PVP via a ripening process.