Controllable nonlinear optical properties of different-sized iron phosphorus trichalcogenide (FePS₃) nanosheets

Two-dimensional iron phosphorus trichalcogenide (FePS3) has attracted significant attention for its use in electricity, magnetism and optical fields due to its outstanding physical and chemical properties. Herein, FePS3 was prepared using the chemical vapor transportation (CVT) method and then exfoliated by using fast electrochemical exfoliation. After gradient centrifugation, FePS3 nanosheets with thicknesses ranging from 1.5 to 20 nm and lateral dimensions of 0.5-3 μm were obtained. By utilizing the spatial self-phase modulation (SSPM) effect, the relationships between the nonlinear refractive index and the size of the FePS3 nanosheets were investigated in detail which revealed that the nonlinear refractive index can be effectively controlled by the size of the FePS3 nanosheets. It is worth noting that the optimal FePS3 nanosheets (3-5 layers thick and ∼1 μm in lateral dimensions) displayed the highest nonlinear refractive index of ∼10-5 cm2 W-1. This work demonstrates the potential that FePS3 nanosheets have for use in nonlinear optics or nonlinear optical devices.