Synthesis of short-chain passivated carbon quantum dots as the light emitting layer towards electroluminescence

Short-chain passivated fluorescent carbon quantumdots (S-CQDs) with graphitic structure were synthesized via a one-step hydrothermal approach using phthalic acid with a benzene ring conjugated structure as the carbon source and ethylenediamine as a nitrogenous additive. The synthesized S-CQDs have an average diameter of 5.53 nm and exhibit excitation-dependent photoluminescence emission. The S-CQD aqueous solution emits bright blue light under ultraviolet excitation with a quantum yield of 29.3%. The optical band gap of the S-CQDs was calculated to be 4.26 eV, the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels of -8.35 and -4.09 eV were obtained for the S-CQDs by cyclic voltammetry. In addition, the S-CQDs have a good film-forming ability, as confirmed by atomic force microscopy analysis. By virtue of the structure characteristics, optical properties and the filmforming ability of S-CQDs, quantum dot-based electroluminescent light emitting diodes (QD-LEDs) were fabricated by a solution processing method with S-CQDs as the emitting layer, which emits blue light at 6-9 V driving voltage, showing that the S-CQDs have promising prospects for application in QD-LEDs.