Tunable light emission from carbon dots by controlling surface defects

Carbon dots(CDs)are metal-free fluorescent materials that can be used in optical and electronic devices,but few studies have focused on one-step synthesis routes for CDs with tunable color and high photoluminescence quantum yield(PLQY).Herein,CDs with tunable light emission were synthesized using a novel amide-assisted solvothermal approach.The as-prepared CDs were well dispersed and homogeneous,with average diameters of approximately 2.0–4.0 nm,depending on the dopants.Owing to the surface states with different ratios of nitrogen-and oxygen-related species,different CDs can exhibit blue,green,red,or white emission with relatively high PLQYs of 61.6%,41.3%,29.1%and 19.7%,respectively.XPS measurements,in conjunction with DFT calculations,indicate that nitrogen substitution(pyridinic/pyrrolic nitrogen)dominates the blue emission,while introducing oxygen functional groups lowered the LUMO energy level,which resulted in redder emission.In addition,the CDs are demonstrated as a bioimaging probe in both in vitro and in vivo assays,and the white light CDs have been demonstrated to be potential fluorescent materials for white-light-emitting diode(WLED).