Niobium Carbide MXenes with Broad-Band Nonlinear Optical Response and Ultrafast Carrier Dynamics

Exploring the nonlinear photonics of emerging promising two-dimensional (2D) materials like MXenes will boost the development of broad-band optoelectronic and photonic applications. In this paper, the broad-band nonlinear optical response and the excited-carrier dynamics of an emerging MXene, Nb₂C, are systematically investigated for the wavelength range of visible to the near-infrared band. The obtained nonlinear optical response shows a wavelength and excitation intensity dependence. The imaginary part of the third-order nonlinear optical susceptibility Imχ⁽³⁾ and figure of merit were found to be -1.4 × 10^-10 esu and 7.5 × 10^-12 esu cm, respectively. The interesting nonlinear absorption response inversion properties (e.g., a shift from saturable absorption to two-photon absorption) of Nb₂C nanosheets in the near-infrared promise possible important applications in nonlinear photonics, such as an optical switch. We also demonstrate that the wavelength-dependent relaxation times consist of two different relaxation components, that is, time constants in which one is hundreds of femtoseconds and the other is several picoseconds. Our results indicate promising potential in near-infrared nanophotonic applications of 2D Nb₂C and offer a promising candidate for 2D-material-based nanophotonic devices and beyond.