Tailored MXene quantum dots for ultrafast laser photonics: engineering nonlinear optical properties for high-performance mode-locking

MXene quantum dots (MQDs) have recently attracted increasing attention as zero-dimensional derivatives of MXenes with enhanced quantum confinement effects, tunable surface chemistry, and broadband nonlinear optical responses. This review provides a focused and critical synthesis of recent advances in Ti3C2Tₓ and V2C MQDs for ultrafast laser photonics. The current literature on synthesis strategies – including electrochemical exfoliation, HF-free solvothermal routes, and laser ablation – is systematically examined in relation to size control, surface termination engineering, and defect regulation. Reported nonlinear optical mechanisms, such as saturable absorption (SA), reverse saturable absorption (RSA), and two-photon absorption (TPA), are comparatively analyzed with emphasis on their impact on pulse duration, modulation depth, saturation intensity, and operational stability in fiber and solid-state laser systems. Broadband compatibility across the 1.0–1.55 µm spectral region and device-level integration strategies are discussed to clarify structure – property – performance relationships. By consolidating dispersed findings and identifying material and device-level challenges, this review outlines key design principles and future directions for engineering MQDs as stable and high-performance saturable absorbers in next-generation ultrafast photonic systems.