Solvothermal Synthesis and Ultrafast Photonics of Black Phosphorus Quantum Dots

Ultrasmall black phosphorus quantum dots (BPQDs) with an average size of 2.1 ± 0.9 nm are synthesized by using a solvothermal method in a N ‐methyl‐2‐pyrrolidone solution. Verified by femto‐second laser Z‐scan measurement, BPQDs exhibit excellent nonlinear optical response with a modulation depth of about 36% and a saturable intensity of about 3.3 GW cm −2 . By using BPQDs as optical saturable absorber, the ultrashort pulse with a pulse duration of about 1.08 ps centered at a wavelength of 1567.5 nm is generated in mode‐locked fiber laser. These results suggest that BPQDs may be developed as another kind of promising nanomaterial for ultrafast photonics.