Effect of the Composition on the Nonlinear Optical Response of Au_xAg_1–x Nano-Alloys

Abstract

The synthesis of variable composition Au x Ag (1−x) alloyed nanoparticles prepared by laser ablation in water is reported. The nanoalloys exhibited a single characteristic surface plasmon resonance peak, whose spectral position was lying between the surface plasmon resonance peaks of neat Ag and Au nanoparticles, at about 400 and 530 nm respectively, depending directly on the composition of the alloyed nanoparticles. The nonlinear optical response of the nanoalloys was studied in details under 532 nm (visible) 35 ps and 4 ns laser excitation and it was found to be significant and greatly influenced by the position of the plasmonic band relative to the laser excitation wavelength. In this respect, increase of the Au molar fraction resulted in shifting of the nanoalloy plasmon band toward the location of the plasmon band of neat Au nanoparticles, i.e., at about 530 nm, closer to the laser excitation wavelength, hence causing more efficient resonance enhancement of the nonlinear optical response. Moreover, the nanoalloys were found to exhibit strong saturable absorption behavior when excited by ps or ns pulses, in the latter case this behavior changing to reverse saturable absorption at high laser intensity. The origin, the magnitude and the sign of the observed optical nonlinearities of the alloyed nanoparticles are explained and discussed in terms of the hot-electron and the interband contributions taking place under laser excitation in such nanostructures. The possibility of controlling the magnitude and the sign of the nonlinear optical response of Au x Ag (1−x) nanoalloys through their composition provides an attractive and efficient way to tailor the optical nonlinearities of noble metal nanoalloys, making them very useful for various emerging photonic, biophotonic, and optoelectronic applications.

Enhanced nonlinear optical responses of zinc diaminopyrimidin-2-ylthio phthalocyanine conjugated to AgxAuy alloy nanoparticles

“…This suggests that Ag 1 Au 3 alloy enhanced the OL performance of 2 more than Ag 3 Au 1 as earlier observed in the reported β eff . This observation is also in good agreement with NLO studies carried out on Au x Ag 1 −x nano-Alloys at 532 nm, using 35 ps and 4 ns laser pulses, by Papagiannouli and coworkers [7]. They observed that the alloy with the highest Au content had the strongest limiting properties which were attributed to the proximity of plasmon peak of the alloys to the excitation laser source.…”

“…The intense SPR peaks of Ag 3 Au 1 and Ag 1 Au 3 were observed at 423 nm and 482 nm, respectively, Table 1. The SPR peaks of the alloys are very close to the SPR positions of pure AgNPs and AuNPs, depending on the composition of Ag or Au present in the alloys [7].…”

“…Research focus on optical limiting (OL) properties of metallic nanoparticle is gradually expanding and evolving from monometallic into bimetallic (Ag x Au 1-x ) [5][6][7] nanoparticles. The surface plasmon resonance (SPR) bands of the bimetallic nanoparticles can be tuned to enhance their optical properties depending on the molar compositions of the alloys [8,9].…”

“…The surface plasmon resonance (SPR) bands of the bimetallic nanoparticles can be tuned to enhance their optical properties depending on the molar compositions of the alloys [8,9]. The tuning of the plasmonic bands of Ag-Au alloys covering a broad spectral range make them suitable candidates in biomedicine [10], catalysis [11,12], bio-imaging [13], and nonlinear optical applications [5][6][7]. Papagiannouli et al [7] reported that the optical limiting behavior of Ag x Au 1-x nanoparticles (NPs) (using 35 ps and 4 ns laser pulses) exhibited SPR dependence such that as the SPR peak of the Au-rich alloy NPs red shifted towards the SPR of pure gold NPs, the third-order susceptibility of the alloyed NPs was found to be significantly enhanced.…”

“…Papagiannouli et al [7] reported that the optical limiting behavior of Ag x Au 1-x nanoparticles (NPs) (using 35 ps and 4 ns laser pulses) exhibited SPR dependence such that as the SPR peak of the Au-rich alloy NPs red shifted towards the SPR of pure gold NPs, the third-order susceptibility of the alloyed NPs was found to be significantly enhanced. The plasmonic bands of the alloys were believed to have played vital role in tuning the OL performance of the alloys [7].…”