Regulable nonlinear absorption and ultrafast dynamics process of monolayer Nb2CTx

MXenes, two-dimensional (2D) transition metal carbides and nitrides, were prepared for nonlinear optical research. Here, the nonlinear absorption of two-dimensional (2D) monolayer Nb 2 CT x nanosheets were investigated by nanosecond Z-scan measurements in 532 nm at different laser intensities. It was found out that Nb 2 CTx nanosheets exhibited from saturable absorption (SA) to reverse saturable absorption (RSA). With the increase in incident energies, a switch from SA to RSA occurred under some excitation intensities. Besides, ultrafast carrier dynamics of monolayer Nb 2 CTx nanosheets were also researched by pump–probe technique. The findings suggest that the relaxation includes a biexponential decay process, which consists of a fast decay component and a slow one. Moreover, with the pump fluence increasing, the observed lifetime of fast decay component decreases from 4.3 to 3.7 ps, and the slow decay component decreased from 13.8 to 11.3 ps. These results were usually ascribed to the carrier density dependence on e-ph coupling. It also reveals that monolayer Nb 2 CT x nanosheets can be used to build ultrashort pulse generation and optoelectronic devices.