Green synthesis of V₂C MXene quantum dots with tunable nonlinear absorption for optical limiting applications

Vanadium carbide MXene quantum dots (V₂C QDs) have emerged as promising nanoscale materials with tunable surface chemistry and pronounced quantum confinement effects. Herein, we report a green, HF-free synthesis of highly fluorescent V₂C QDs directly from the MAX phase via pulsed laser ablation in a binary solvent system. The synthesized quantum dots exhibited a production yield of 27% and a narrow size distribution, with an average diameter of 2.5 nm. Furthermore, they exhibit intense and stable photoluminescence with a quantum yield of 11.5%. Their optically tunable emission, combined with excellent optical stability, positions them as strong candidates for high-resolution bioimaging and biosensing applications. We investigated their nonlinear optical response using an open-aperture Z-scan technique at 532 nm, which revealed a dual behavior, namely saturable absorption at low excitation intensities and strong reverse saturable absorption at higher intensities. These materials also show a good optical limiting performance, characterized by a low onset threshold. The unique coexistence of stable fluorescence and robust nonlinear optical properties makes V₂C QDs an attractive option for advancements in laser protection, optoelectronics, and multifunctional biomedical photonics. These results provide a sustainable approach to synthesizing high-quality V₂C QDs and highlight their potential in bridging nanophotonics and biomedicine through versatile optical functionalities.