Facile synthesis and photoluminescence mechanism of green emitting xylose-derived carbon dots for anti-counterfeit printing

The realization of long-wavelength emissions and thoroughly understanding of photoluminescence (PL) mechanism are still huge challenges to be addressed for further development of carbohydrate-derived carbon dots (CDs). Herein, novel CDs with excellent green emission were synthesized from a precursor comprising of xylose and m-phenylenediamine in phosphoric acid solution via a simple microwaveassisted hydrothermal method. The PL efficiency was dependent on the combination of different acids and the precursor as well as the synthesis temperature, while the PL properties were mainly related to the acid base environment of precursor. Optical performance and structural characterization revealed that the oxygen-containing groups and protonated amino groups were mainly responsible for the blue and green emission properties, respectively. Moreover, a multi-center fluorescent mechanism on the different PL performances of xylose-derived CDs was proposed and verified by further investigating the pH-dependent PL behaviors. Based on the switching between green and blue emission in different pH regions, the xylose-derived CDs solution was demonstrated to be a promising fluorescent ink for anticounterfeit printing. This research open a door for value-added utilization of xylose, as well as providing a facile and green strategy for large-scale preparation of CDs. (c) 2019 Elsevier Ltd. All rights reserved.