Ultrafast Transient Spectra and Dynamics of MXene (Ti3C2Tx) in Response to Light Excitations of Various Wavelengths

The novel optical response properties of MXene (Ti3C2Tx) have been applied in many cutting-edge areas, such as solar utilization, laser therapy, and sensing. Understanding the interaction between photons and MXene is critical to all these applications. However, the ultrafast carrier pathway of this material under broad-wavelength-range light excitation remains unknown. In this work, we conducted a comprehensive ultrafast spectroscopy study of MXene under light excitation at various wavelengths. With the combination of ultrabroadband transient spectra (450-1100 nm) and dynamics, we provided schemes for the MXene-light interaction. The transient spectra showed that light excitation in the ultraviolet to near-infrared ranges could induce two transient absorption regions in the visible and near-infrared ranges. An early stage fast relaxation transient spectrum at 100-400 fs is attributed to an electron-electron interaction process. The dynamics in the early stage could be affected by the modulation of the excitation wavelength, the fluence, and the probe wavelength. In addition, the thermal diffusion dynamic process is sensitive to the surroundings and is nearly independent of the excitation wavelength and the fluence, whereas temporal signatures depend linearly on the excitation fluence and the absorption efficiency. Our results could improve the fundamental understanding of MXene-sunlight interaction and applications.