Rare-Earth-modified luminescent two-dimensional nanosheets derived from oxidized Mo₂CT_x MXene

Rare-Earth luminescent (REL) materials are valued for their sharp multiwavelength emissions, photon up- and down-conversion, and strong x-ray absorption. MXenes, in contrast, are highly versatile two-dimensional (2D) materials with exceptional electronic and structural properties, yet their use as REL hosts remains largely unexplored. Here, we demonstrate, for the first time, rare-Earth-modified 2D MXene sheets as luminescent materials, establishing a new pathway for their integration into flexible, multifunctional, and miniaturized photonic systems. Europium (Eu³⁺) ions were incorporated into Mo₂CT_x nanosheets via hydrothermal treatment. At moderate temperature (230 °C), the layered structure was preserved with an expanded interlayer spacing, enabling ∼1-0 at.% Eu³⁺ incorporation into oxygen-rich Mo–O–C domains. At higher temperature (360 °C), the MXene layers collapsed, yielding highly crystalline MoO _x and Mo–O–C phases with increased Eu content (∼15 at.%). Photoluminescence spectra exhibited sharp Eu^3+⁵D₀ → ^⁷F transitions, dominated by a strong emission at 615 nm. The emission intensity was markedly enhanced at higher temperature due to improved Eu incorporation and oxide crystallinity. Importantly, this work establishes a luminescence mechanism in MXenes beyond previously reported quantum dots, demonstrating that layered MXene frameworks themselves can host rare-Earth optical centers. This unique non-quantum dot pathway highlights the potential of REL-functionalized MXenes for space-relevant applications requiring multifunctionality, such as multiwavelength lidar surveillance and communication, photon conversion from infrared and x-rays to visible light, electromagnetic shielding, and radiation protection, while retaining lightweight and mechanically flexible form factors.