Abstract
The nonlinear optical properties of Rh–Pd and Rh–Pt solid-solution alloy nanoparticles (NPs) were experimentally investigated by means of the z-scan technique. The open aperture (OA) measurement showed a reverse saturable behavior, whereas the closed aperture (CA) measurement showed a peak- and valley-shape. Both the Rh–Pd and Rh–Pt NPs exhibited a positive nonlinear optical index of refraction at 800 nm relating to the self-focusing phenomenon. In addition, the nonlinear absorption of the Rh–Pt NPs (4.39 × 10−12 cm/W) was higher than that of the Rh–Pd NPs (1.63 × 10−12 cm/W) due to the small interval between the occupied and unoccupied density of states (DOS) of Rh–Pt than Rh–Pd. The nonlinear responses of the Rh–Pd and Rh–Pt NPs was attributed to the hot electron contribution and the reverse saturation of intraband and interband transitions.
Highlights
Due to the advanced technique for the preparation of nanoparticles (NPs) with well controlled size, structure and composition, it is possible to extend the study on nonlinear optical properties from organic materials to NPs based systems
It is seen from UV-visible spectra that the surface plasmon resonance (SPR) peaks of Rh–Pd and Rh–Pt are at 270 and 250 nm, respectively
At high intensity, the hot electrons excited by laser pulses through the intraband absorption in the conduction band and the multiphoton absorption between the d band and the conduction band can be further excited to a higher excited state in the conduction band, which is so-called excited state absorption (ESA) or free carrier absorption
Summary
Due to the advanced technique for the preparation of nanoparticles (NPs) with well controlled size, structure and composition, it is possible to extend the study on nonlinear optical properties from organic materials to NPs based systems. Ganeev et al [22] reported the nonlinear optical properties of Au, Pd, Pt and Ru NPs using the z-scan technique with different pulse durations at 792 nm They have reported a self-focusing effect of Pd NPs. When the sample was pumped by 120 fs pulse, positive nonlinear absorption was found over a broad range. Ganeev et al [23] had investigated the nonlinear absorption and refraction of Ru, Pd, and Au NPs using the z-scan technique with 50 ps laser pulses at 1064 nm and found that the Pd NPs exhibited a self-defocusing effect and positive nonlinear absorption.
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