Enhanced Nonlinear Optical Absorption Properties and Carrier Dynamics of Violet Phosphorene by Oxidation for Ultrafast Photonic Applications

Violet phosphorene, an emerging two‐dimensional semiconductor material, demonstrates unique potential for optoelectronics. Here, the effect of oxidation treatment on the nonlinear optical absorption and carrier dynamics properties of two‐dimensional violet phosphorene nanosheets was investigated. The results reveal that partially oxidized violet phosphorene exhibits enhanced saturable absorption properties and significantly shortened carrier relaxation lifetimes. X‐ray photoelectron spectroscopy and first‐principles calculations indicate that the introduction of oxygen atoms forms P=O and P–O–P bonds, leading to a p‐orbital hybridization and a restructuring of the electronic structure. This shifts the valence band maximum upward and lowers the conduction band minimum due to oxygen defect states, resulting in a reduced bandgap and optimized carrier dynamics. For further verification, passively Q‐switched and mode‐locked lasers operating at 1 μm were demonstrated, utilizing two‐dimensional violet phosphorene and oxidized violet phosphorene nanosheets as saturable absorbers, respectively. Compared with violet phosphorene‐based lasers, oxidized violet phosphorene‐based pulsed lasers achieve better pulse‐width compression in both passively Q‐switched and mode‐locking operations (passively Q‐switched: 343.52 ns vs 412.81 ns; mode‐locking: 290 fs vs 404 fs). These results confirm that oxidation engineering effectively enhances the ultrafast nonlinear optical responses of two‐dimensional violet phosphorene, laying a foundation for optimizing its optoelectronic properties and ultrafast photonics applications.