Full color fluorescent carbon quantum dots synthesized from triammonium citrate for cell imaging and white LEDs

Multicolor fluorescent carbon quantum dots (CDs) exhibit prospective applications but the intrinsic reaction and luminescence mechanisms of CDs remain unclear. In this work, full color fluorescent CDs were synthesized through a facile solvothermal treatment with triammonium citrate as the carbon source. By adjusting the reaction temperature, the maximum emission wavelength is tuned from 440 nm for blue CDs (B-CDs) to 625 nm for red CDs (R-CDs), covering the whole visible spectrum range. The emission mechanism is proposed as surface-state-controlled, which results from different degrees of graphitization and increasing of functional groups on the surfaces. Three different surface states are derived from the overlap of the absorption and excitation spectra and the mechanism is established by XRD, Raman, XPS and UV–Vis absorption. The full-color luminescent CDs with high light and pH stability as well as good biocompatibility are successfully employed to image HeLa cells. White LED is fabricated by B-, G-, and R-CDs/polymer films with a near ultraviolet (NUV) semiconductor chip. The results of this research demonstrate that the synthesized CDs can be potentially applied in multi-color displays, white LEDs and biological imaging probes.