Third-Order Nonlinear Optical Properties of Aqueous Silver Sulfide Quantum Dots
Marta Gordel, Magdalena Malik, Agnieszka Siomra, Marek Samoć, Marcin Nyk
Abstract
Wide spectral wavelength range (500–1600 nm) measurements of nonlinear optical properties of silver sulfide (Ag 2 S, with 2- or 3-mercaptopropionic acid, 2 or 3MPA ligands) quantum dots (QDs) in aqueous colloidal solutions were performed using the Z-scan technique with tunable ∼55 fs laser pulses at 1 kHz. We have identified regions of the occurrence of various NLO effects including two-photon absorption, nonlinear refraction, as well as saturation of one-photon absorption. At the same time, we evaluated the relationship between the properties of the QDs and the variation of the material that covers their surface. The peak two-photon absorption cross section (σ 2 ) values were determined to be 632 ± 271 GM (at 850 nm) for Ag 2 S-2MPA QDs and 772 ± 100 GM (at 875 nm) for Ag 2 S-3MPA QDs. The physicochemical factors influencing the three-dimensional self-organization of Ag 2 S QDs in water as well as their impact on spectroscopic properties were also investigated.