Nanosilver from nano-AgBr: synthesis, surface chemistry, and nonlinear optical properties

Abstract

We report preparation of silver nanoparticles in the 10 nm size range by exhastive reduction of a well-known and well-characterized AgBr nanosol. These silver nanoparticles exhibit a second order hyperpolarizability tensor, β=(100±10) x 10 -30 esu per atom. The nanoparticles chmisorb a monolayer of iodide ions with concomitant bleaching of the surface plasmon absorption but no attenuation of Hyper-Rayleigh (second harmonic light) Scattering (HRS). Further addition of iodide leads to significant enhancement of HRS, which we attribute so surface-enhanced second harmonic scattering (SESHS) from iodide ion physisorbed on the AgI adlayer. A merocyanine dye, which does not exhibit HRS in solution, chemisorbs as a monolayer to the nanosilver, with formation of J-aggregates. These aggregates, like the free dye, are not active in second harmonic scattering. Further addition of dye leads to HRS enhancement, which we interpret as physisorption of dye onto the J-aggregate monolayer; the non-centrosymmetric surface environment allows observation of SESHS. A lower-limit estimate of the second order hyperpolarizability of the adsorbed dye is 200 X 10 -30 esu per molecule.