Elucidation of size, structure, surface plasmon resonance, and photoluminescence of Ag nanoparticles synthesized by pulsed laser ablation in distilled water and its viability as SERS substrate

In the present work, silver nanoparticles have been synthesized as a function of laser irradiation time and incident laser fluence by focusing a second harmonic of a Q-switched Nd:YAG laser. Increase in the irradiation time from 5 to 30 min at fixed incident laser fluence of ~ 10 J/cm2 per pulse resulted in a decrease in the average size of the nanoparticles from 20 to 15 nm, respectively. The average size of the nanoparticle was further reduced to 10 nm by increasing the incident laser fluence to ~ 22 J/cm2 at fixed irradiation time of 30 min. The reduction in the size of the nanoparticles from 20 to 15 nm induced a blue shift in the plasmonic peak from 403 to 398 nm, but with further decrease in size, a reversing of the peak towards longer wavelength was observed. The structural features of the nanoparticles exhibited dependence on both the process parameters as revealed by the X-ray diffraction, selected area electron diffraction, and high-resolution transmission electron microscope images. Longer irradiation time and higher incident fluence resulted in more oxidized phases of silver nanoparticles. These nanoparticles were found to be photoluminescent, having broad emission around the plasmonic excitation wavelength. A study on the effect of the particle size and concentration of the synthesized silver nanoparticles on its viability as surface-enhanced Raman scattering substrate for a bioactive furanoflavonoid, karanjin is reported.