Minimized thermal effects and strong two-photon absorption of aluminum, silver doped platinum bi-metal nanoparticles

Abstract

Herein, for the first time, we have investigated the strong nonlinear optical (NLO) properties aided with minimal thermo-optical effects in silver-platinum (Ag-Pt) nanoparticles (NPs) using Z-scan technique with high repetition rate femtosecond pulses at 700 nm. The NPs were synthesized using ultrafast laser ablation of Ag/Al targets immersed in the Pt colloidal solutions in isopropyl alcohol (IPA). We observed reverse saturable absorption (RSA)/two-photon absorption (2PA) behavior in Ag-Pt NPs (with 0.5 mM concentration of Pt), W-shaped switching behavior in Ag-Pt NPs (with 1 mM concentration of Pt), and RSA/2PA behavior in Ag-Pt NPs (with 3 mM concentration of Pt). The multiple-stage nonlinear absorption phenomenon is attributed to the interchange of pure 2PA or excited-state absorption, and 2PA saturation effects. Additionally, the broadband third-order NLO properties of aluminum-doped Pt (Al-Pt) bi-metallic NPs were obtained using spectral-dependent Z-scan studies at 700 nm, 800 nm, and 900 nm. The results revealed that Al-Pt bi-metallic NPs exhibited strong saturable absorption (SA), 2PA, and switching from SA to RSA. It is also revealed from the closed aperture Z-scan data that Ag-Pt and Al-Pt bi-metallic NPS exceed thermal contribution with strong 2PA coefficients unprecedented for single metal NPs. In the case of Ag-Pt NPs, strong 2PA saturation effects are attributed to the filling of Ag-O anti-bonding states by the photo-excited electrons and then charge transfer to the Pt plane. In the case of Al-Pt NPs, strong 2PA phenomena are ascribed to the enhancement of charge carriers in the conduction band and, hence, the strong surface plasmon resonances. The 2PA coefficients were evaluated to be ∼10−7 cm/W. The superior and switching NLO effects indicate that these materials might be utilized for potential applications, including optical modulators, and all-optical switching devices.