Solvent-Engineered Synthesis of Multicolor Emissive Carbon Dots from Citric Acid and Cyanamide

Multicolor emissive carbon dots (CDs) have received increasing attention due to their excellent optical features. By far, insufficient studies have been conducted on the preparation and modulation of multicolor CDs, and most of the precursors used for the synthesis of multicolor CDs own benzene rings. Here, we report the solvent-engineered preparation of CDs with bright multicolor emissions. The CDs are fabricated by hydrothermal/solvothermal treatment of citric acid and cyanamide, circumventing the use of precursors containing aromatic molecules as well as the medium of concentrated acids. By simply changing the reaction solvent, the emission wavelength of the CDs shifts from the blue to yellow region, and even white emissive CDs are obtained. Specifically, blue, cyan, yellow, and white emissive CDs are obtained to exhibit photoluminescence quantum yields (PL QYs) ranging from 19.7% to 62.3%. Further studies show that the bright fluorescence might originate from molecular fluorophore grafting on the CD surface. Moreover, CDs/polymer composites with uniform bright luminescence are prepared and used as fluorescent color-converting materials for fabricating multicolor LEDs. This study extends the modulated preparation of multicolor emissive CDs that are potentially useful for optoelectronic applications.