Ultraviolet emissive Ti3C2Tx MXene quantum dots for multiple anti-counterfeiting

The development of advanced anti-counterfeiting is an important and urgent task for civil, commercial and military applications. Herein, multiple anti-counterfeiting was performed by using the dispersion of Ti3C2Tx MXene quantum dots (MQDs) as luminescent ink. The ultraviolet emissive MQDs were prepared for the first time by decreasing their oxidation degree. Compared with the MQDs obtained by the microwave heating, the oxidation degree of the MQDs treated by ethanol refluxing reduced from 38% to 23%, the ultraviolet emission peak blue-shifted from 307 to 299 nm, and the quantum yield raised by four times. Simultaneously, the colloidal stability, photostability, thermal stability and pH stability were also greatly enhanced. Based on the excitation-dependent luminescence properties of the MQDs with low oxidation degree, multiple anti-counterfeiting was developed using the colorless and transparent MQD dispersion. The concealed pattern was recognized for a preliminary judgement by bare-eyes with the illumination of a 365 nm ultraviolet lamp, resulting from the blue luminescence of MQDs. As for the high-level anti-counterfeiting, a more legible ultraviolet luminescent pattern was presented by an adaptive focus imaging spectrograph with 254 nm excitation. This study unlocks the ultraviolet photoluminescence of MQDs and furnishes a novel candidate for advanced anti-counterfeiting.