A facile synthesis of broad plasmon wavelength tunable silver nanoparticles in citrate aqueous solutions by laser ablation and light irradiation

A complete light based synthesis of silver nanoparticles of different shapes exhibiting strong and broad band plasmon resonances is demonstrated in aqueous solutions of single reagent tri-sodium citrate (TSC). This method involves synthesis of almost spherical nanoparticles using liquid phase pulsed laser ablation (LPPLA) followed by their photo-mediated shape transformation into triangular nanoplates by visible light irradiation. UV-vis spectroscopy and Mie theory based analytical calculations show that this method can produce high concentrations of nanoparticles at optimum TSC concentration. LPPLA method is shown to be potential for producing relatively smaller size, isolated spherical silver nanoparticles at optimum TSC concentration without aid of strong reducing agents like borohydrides. This method has also resulted interconnected nanoparticle networks in pure water or at very low TSC concentrations. These isolated spherical nanoparticles were further shown to act as seed particles for high yield synthesis of nanoplates. The concentration of TSC played a vital role in producing both highly stable spherical nanoparticles and their photo-mediated shape transformation into triangular nanoplates. At the optimum TSC concentration of about 10 mM, pH about 7.5 and visible light irradiation of about 24 h, the produced triangular nanoplates have shown strong plasmon absorption in visible to near NIR region, useful for solar light harvesting applications. Further during the light irradiation, presence of additional silver ions in the nanoparticle solution initially increased the growth of spherical nanoparticles which finally resulted in high yield formation of triangular nanoplates.