Room-temperature phosphorescence in coal-based humic acid-derived carbon dots

Coal-derived carbon dots inherit the rich functional groups of raw coal, which makes them easy to be modified, and have important applications in chemical analysis, biomedicine, optoelectronic devices and other fields due to their excellent properties. In this work, we achieved room-temperature phosphorescence (RTP) emission of coal-based humic acid-derived carbon dots (HACDs) in boric acid for the first time. The results show that the boron-carbon bonds are prone to generate between HACDs and boric acid under heating conditions. Besides, the surface of the prepared HACDs contains numerous phenolic hydroxyl groups, which are easily oxidized by hydrogen peroxide into carbonyl groups, improving the phosphorescence lifetime. The resultant RTP materials exhibit an ultra-long phosphorescence lifetime of 632.20 ms with an outstanding afterglow as long as 9.0 s, and the phosphorescence quantum yield is 7.6%. This work provides guidance for finding earth-abundant and cost-effective carbon sources and a novel means to modulate the emission mechanism of coal-derived carbon dots. Coal-based humic acid derived carbon dots are first prepared as room temperature phosphorescent materials using an innovative, simple and large-scale method, developing a new direction to modulate the emission mechanism of coal-derived carbon dots.