R. Philip et al., Picosecond optical nonlinearity in monolayer-protected gold, silver, and gold-silver alloy nanoclusters, PHYS REV B, 62(19), 2000, pp. 13160-13166
Monolayer-protected Au, Ag, and Au:Ag alloy nanoclusters have been synthesi
zed using octanethiol and octadecanethiol as capping agents. The particle-s
ize distribution is narrow with an average core size of 3-4 nm. Optical non
linearity induced by 35 ps pulses at 532 nm has been investigated in these
samples using the Z-scan technique. It is found that in general, they behav
e either as saturable absorbers or reverse saturable absorbers depending on
the intensity of excitation. Au and Ag clusters show nearly the same effic
iency for optical limiting, but the alloy clusters are found to be less eff
icient in limiting and are less photostable. The observed effects are expla
ined in terms of the electron dynamics of the excited-state species.