Acid catalyzed microwave-assisted production of full-color light emissive carbon quantum dots for CCT-tunable WLEDs

Many studies have examined the use of multicolor light emissive carbon quantum dots (CQDs) in toxic metal-free optoelectronic devices, but it is still limited to obtain desirable optical properties. Here, we present a straightforward synthetic route for producing multicolor light emissive nitrogen-doped carbon quantum dots (NCQDs) using a microwave-assisted process, thus yielding individual color emissions of NCQDs in a batch. The emissive colors from NCQDs can be controlled by adjusting the molar ratios of citric acid and urea from 1 to 6 for blue and green-light emission, respectively. When o-phenylenediamine (oPDA) was chosen as a precursor, the resulting NCQDs can emit yellow light, while the red light emissive NCQDs can be obtained in the presence of a diluted HCl as a catalyst for accelerating and extending sp2-carbon bonding. The doped nitrogen in NCQDs was found to be formed as a graphitic nitrogen in the core, leading to red-shifted photoluminescent emissions from 450 nm to 620 nm. To fabricate white-light emitting diodes (WLEDs), the mixing ratios of NCQDs with different light emissions in polydimethylsiloxane (PDMS) were varied to control the correlated color temperature (CCT) from 3386 K to 7151 K and CIE coordinates of (0.30, 0.32), (0.32, 0.36), and (0.40, 0.37).