Synthesis of multi-color fluorescent carbon quantum dots and solid state CQDs@SiO2 nanophosphors for light-emitting devices

Carbon quantum dots (CQDs) with multi-color emission are synthesized through hydrothermal method by varying the ratio of citric acid (CA) and urea, the solvent (water, ethyl alcohol, and dimethylformamide), the hydrothermal temperature, and reaction time. The CQDs emit bright fluorescence which can be gradually tuned from blue to red continuously, almost covering the whole visible spectrum. The emission peaks of the CQDs shift from 450 nm to 650 nm with the surface groups and structures changing. Importantly, all solid state CQDs@SiO2 nanophosphors are successfully synthesized by reversed-phase micromulsion method. Based on these solid state phosphors, multi-color CQDs@SiO2 phosphors-based light-emitting diodes (LED) and white light-emitting diode (WLED) with a Commission Internationale de L' Eclairage (CIE) value of (0.3497, 0.3045) are fabricated in a low-cost, environment-friendly way.