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Metallic nanoparticles have gained attention in technological fields, particularly photonics. The creation of silver/gold (Ag/Au) alloy NPs upon laser exposure of an assembly of these NPs was described. First, using the Nd: YAG pulsed laser ablation's second harmonic at the same average power and exposure time, Ag and Au NPs in distilled water were created individually. Next, the assembly of Ag and Au NP colloids was exposed again to the pulsed laser, and the effects were examined at different average powers and exposure times. Furthermore, Ag/Au alloy nanoparticles were synthesized with by raising the average power and exposure time. The absorption spectrum, average size, and shape of alloy NPs were obtained by using an ultraviolet-visible (UV–Vis) spectrophotometer and transmission electron microscope instrument. Ag/Au alloy NPs have been obtained in the limit of quantum dots (<10 nm). The optical band gap energies of the Ag/Au alloy colloidal solutions were assessed for different Ag/Au alloy NP concentrations and NP sizes as a function of the exposure time and average power. The experimental data showed a trend toward an increasing bandgap with decreasing nanoparticle size. The nonlinear optical characteristics of Ag/Au NPs were evaluated and measured by the Z-scan technique using high repetition rate (80 MHz), femtosecond (100 fs), and near-infrared (NIR) (750–850 nm) laser pulses. In open aperture (OA) Z-scan measurements, Ag, Au, and Ag/AuNPs present reverse saturation absorption (RSA) behavior, indicating a positive nonlinear absorption (NLA) coefficient. In the close-aperture (CA) measurements, the nonlinear refractive (NLR) indices (n2) of the Ag, Au, and Ag/Au NP samples were ascribed to the self-defocusing effect, indicating an effective negative nonlinearity for the nanoparticles. The NLA and NLR characteristics of the Ag/Au NPs colloids were found to be influenced by the incident power and excitation wavelength. The optical limiting (OL) effects of the Ag/Au alloy solution at various excitation wavelengths were studied. The OL effect of alloy NPs is greater than that of monometallic NPs. The Ag/Au bimetallic nanoparticles were found to be more suitable for optical-limiting applications. [ABSTRACT FROM AUTHOR]

In this study, a simple two step method is employed to sequentially synthesize bimetallic core/shell nanoparticles (NPs). In the first step, pure mono Au and Ag NPs are prepared via 1064 nm pulsed laser ablations in liquid. In the second step, the Au/Ag substrate immersed in the Au/Ag colloidal solution is exposed to the nanosecond laser at 1064 nm wavelength using various laser energies and ablation periods. The crystalline phase and morphology of the bimetallic core/shell NPs (Au/Ag, Ag/Au) are examined by x-ray diffraction and scanning electron microscopy, respectively. The results showed that highly crystalline, well-dispersed spherical monometallic and bimetallic core/shell NPs can be synthesized via pulse laser ablation in liquid. The average diameter of Au, Ag, Au/Ag, and Ag/Au NPs is 34, 40, 58, and 43 nm, respectively. With increasing laser energy, the plasmonic absorption peak of Au NPs redshifts and that of Ag NPs blueshifts. For core/shell, two plasmonic peaks were observed, each of which shifted with increasing ablation time for shell material. Organic dyes with concentrations of 10 − 5 M of methylene-blue with NaBH 4 of 0.05M and methylene-orange with NaBH 4 of 0.1M are used to examine the catalytic performance of the NPs. The core/shell NPs performed better than monometallic NPs. In particular, the catalytic degradation efficiency of Au/Ag and Ag/Au NPs is approximately 90% in significantly less time than monometallic Au and Ag NPs. [ABSTRACT FROM AUTHOR]