Multicolor Carbon Dots Prepared by Single-Factor Control of Graphitization and Surface Oxidation for High-Quality White Light-Emitting Diodes

In a reaction system of asparagine and p-phenylenediamine, blue, green, orange, and red carbon dots (CDs) are successfully prepared by adjusting the ratio of the two reactants. The obtained multicolor CDs have excellent stable properties and high fluorescence quantum yields (up to 74%). Clarifying the luminescence mechanism of multicolor CDs is based on the investigation of the composition, structure, and fluorescence properties of the CDs combined with quantum chemistry calculations. A high-quality white light-emitting diode (LED) with CIE color coordinates (0.33, 0.33) is successfully fabricated using a multicolor CD-epoxy resin composite, and its color temperature and color rendering index are 5612 K and 94, respectively. It is of great significance to prepare multicolor CDs with high fluorescence quantum yields by single-factor control. Using multicolor CDs to fabricate standard white LEDs close to sunlight will significantly increase the practical application value of CDs.