Due to the outstanding electronic properties, unique chemical surface termination units and rich elemental compositions, MXenes have become promising candidates for the development of new generation optoelectronic devices. However, there is still a gap between advanced photonics applications and fundamental understanding of ultrafast carrier photo-physics dynamics and a nonlinear optical response in layered MXenes. Here, we present insight into the excited state relaxation processes and nonlinear optical response of few-layer Ti₃CN and Ti₃C₂ nanosheets (NSs) via transient absorption spectroscopy and Z-scan measurements. Owing to similar structural compositions, the transient absorption and nonlinear absorption characteristics behave totally opposite. In addition, photo-induced bandgap renormalization and Pauli blocking phenomena exist in Ti₃C₂ and Ti₃CN NSs, respectively. The element replacement may be a new strategy for tunable carrier kinetics and nonlinear optical response of MXenes. These research studies may provide insight into ultrafast carrier photo-physics dynamics as well as promote MXene-based advanced photonics and their applications in optoelectronic devices.

中文翻译：

---

通过元素替换定制 MXenes 的超快和非线性光子学

由于出色的电子特性、独特的化学表面终止单元和丰富的元素组成，MXenes 已成为开发新一代光电器件的有希望的候选者。然而，高级光子学应用与对超快载流子光物理动力学和分层 MXene 中的非线性光学响应的​​基本理解之间仍然存在差距。在这里，我们本洞察激发态弛豫过程和少层的Ti的非线性光学响应₃ CN和Ti ₃ Ç _2个纳米片（NSS）经由瞬态吸收光谱和 Z 扫描测量。由于相似的结构组成，瞬态吸收和非线性吸收特性表现完全相反。此外，Ti ₃ C ₂和Ti ₃ CN NSs中分别存在光致带隙重整化和泡利阻塞现象。元素替换可能是 MXenes 可调载流子动力学和非线性光学响应的​​新策略。这些研究可能有助于深入了解超快载流子光物理动力学，并促进基于 MXene 的先进光子学及其在光电器件中的应用。