Illuminating MXene quantum dots: from surface chemistry to white lasing via photoluminescence mechanisms and spectral engineering.

MXene quantum dots (MQDs) have emerged as a distinctive class of zero-dimensional nanomaterials that combine strong quantum confinement with rich surface chemistry, enabling highly tunable photoluminescence (PL) properties. This review provides comprehensive mechanistic insight into the fundamental origins of PL in MQDs, emphasizing the interplay between core electronic structure, surface functional groups, edge states, and defect-mediated excited-state processes. Unlike conventional semiconductor quantum dots, MQD emission is governed by hybridized electronic states arising from transition-metal d orbitals coupled with surface terminations, heteroatom dopants, and hydrogen-bonded networks. We systematically analyze how surface chemistry, quantum confinement, and post-synthetic modifications regulate exciton formation, radiative and nonradiative recombination pathways, and excitation-dependent or excitation-independent emission behaviors. Advanced strategies for spectral engineering, including heteroatom doping, ligand passivation, defect control, and hybridization, are critically discussed in relation to multicolor emission, two-photon luminescence, and nonlinear optical responses. Special attention is given to recent breakthroughs in white emission and coherent white lasing enabled by MQDs, highlighting their potential in advanced photonic and optoelectronic applications. This review establishes a unified framework linking chemical design to excited-state engineering, offering guidance for the rational development of high-performance MXene-based luminescent nanomaterials.