Microscopic nonlinear optical activities and ultrafast carrier dynamics in layered AgInP2S6

Abstract

Since the emergence of graphene, transition metal dichalcogenides, and black phosphorus, two-dimensional materials have attracted significant attention and have driven the development of fundamental physics and optoelectronic devices. Metal phosphorus trichalcogenides (MPX3), due to their large bandgap of 1.3–3.5 eV, enable the extension of optoelectronic applications to visible and ultraviolet (UV) wavelengths. Micro-Z/I-scan (μ-Z/I-scan) and micro-pump-probe (μ-pump-probe) setups were used to systematically investigate the third-order nonlinear optical properties and ultrafast carrier dynamics of the representative material AgInP2S6. UV-visible absorption spectra and density functional theory (DFT) calculations revealed a quantum confinement effect, in which the bandgap decreased with increasing thickness. The two-photon absorption (TPA) effect is exhibited under the excitation of both 520 and 1040 nm femtosecond pulses, where the TPA coefficient decreases as the AgInP2S6 thickness increases. In contrast, the TPA saturation intensity exhibits the opposite behavior that the TPA saturation is more likely to occur under visible excitation. After the valence band electrons undergo photon transitions to the conduction band, the non-equilibrium carriers relax through non-radiative and defect-assisted recombination. These findings provide a comprehensive understanding of the optical response process of AgInP2S6 and are a valuable reference for the development of optoelectronic devices.