Fluorine-Free, Auger-Resistive, and UV-Emitting MXene Quantum Dots

MXene quantum dots (MQDs), in contrast to their precursor metallic MXenes, display photoluminescence (PL), and with the advantages of non-toxicity, ease of synthesis, and low cost, they are promising quantum materials for optoelectronic and photonic devices. However, as-synthesized MQDs suffer from low quantum yield (QY) and a large Stokes shift, limiting efficient UV emission, and are subject to Auger recombination, that is, a severe decline of QY and PL lifetime with increasing exciton density. Here, fluorine-free Ti₂N MQDs are synthesized using a single-step solvothermal process, which emits UV light of a peak wavelength of 370 nm with a greatly improved QY of 17.4%, and superior resistance to Auger recombination. Band structure calculations and X-ray photoelectron spectroscopy measurements indicate that Ti₂N MQDs synthesized by using the solvothermal process are free of fluorine which is normally prevalent on the surfaces of MQDs prepared by an ordinary hydrothermal process. The results shed light on the mechanism of improving QY and mitigating Auger recombination of MQDs helping their practical applications, especially for photonic devices in the UV range.