Multi-color carbon dots for white light-emitting diodes

Heteroatom doped carbon dots (CDs) with color adjustable properties have attracted extensive attention. The doping of elements can effectively tune the surface chemical properties of CDs, thus resulting in its multi-functional applications such as in bio-imaging, photocatalysis, and photothermal conversion. The facile preparation of single metal-doped CDs with color-tunable properties has been rarely reported yet. Herein, we report a one-step solvothermal method to synthesize CDs with different fluorescent emission varying from red to purple to blue. The luminescence characteristic of CDs can be tuned by simply controlling the ratio of precursors, with the emission wavelength correspondingly adjusted from 610 nm to 390 nm. XPS investigation further demonstrated that the color variation is mainly due to the doping of zinc, which will increase the degree of surface oxidation in the as-prepared CDs. For blue emission CDs, the content of graphitic carbon gradually decreases with the rising of zinc chloride addition, while oxygen content remains around 20%, compared with red emission CDs of which the oxygen content is only 4.42%. We also demonstrated with theoretical simulations that the Zn dopant and the functional groups including –C[double bond, length as m-dash]O, –C–OH, –NH(2), and pyrrolic N, play an important role in color change. Furthermore, the synthesized CDs have been successfully used into the fabrication of white LEDs. More than that, we produced a sensitive sensor from the prepared CDs for the effective detection of a variety of colorless transparent organic solvents utilizing the robust fluorescence properties of CDs, showing their great potential as fluorescent probes for chemical sensing.