Multicolor carbon dots: Induced by sp2-sp3 hybridized domains and their application in ion detection and WLED

The heteroatom doping to achieve carbon dots has played a crucial part in exploring the fluorescence mechanism of multicolor emissions, which is closely related with the application development of such materials. Herein, a facile method was developed to synthesize three-color CDs via the co-doping of S and N elements with the assistance of ethanol solvent. The achieved CDs mainly emit blue, green and red lights, yet the photoluminescence quantum yields (FLQYs) generally decreases from 54.0% for B-CDs, 11.5% for G-CDs to 8.5% for R-CDs, respectively. Optical and structural characterizations of these CDs show that the variation of sp2-sp3 hybridized domains resulted from the elements doping (S, N) fundamentally determines the color of CDs. The highest FLQYs of B-CDs in all CDs gives it an advantage to detect metal ions, which finds strong quenching only toward Ag+ because of the interaction between Ag+ and the cores. Likewise, these multicolor CDs attempt to fabricate CDs@PVP composite film emitted white-light as well as a clad material of WLED devices. The results indicate that the correlated color temperatures (CCT) in the ranges of cold and warm white lights can be obtained with different color rendering indexes (CRI) and luminous efficacies. Moreover, CCT and CRI are nearly up to the extremum at the same current value with increasing currents, implying that such CDs are potential as a kind of fluorescent nanomaterial to applicate to WLED device.