Tuning the Dual-Color Fluorescence Emission of Nitrogen-Doped Carbon Dots by Changing Nitrogen Doping Amounts.

A series of nitrogen-doped photoluminescent carbon dots (N-doped CDs) with a proper quantum yield was prepared through microwave-assisted pyrolysis of citric acid and urea as the carbon and nitrogen sources, respectively. The obtained N-doped CDs were fully characterized by high-resolution transmission electron microscopy, elemental analysis, Fourier transform infrared spectroscopy, and X-ray diffraction pattern. The average size of the synthesized N-doped CDs was determined using high-resolution transmission electron microscopy analysis was approximately 7 nm and the interlayer distance was 0.29 nm, which was consistent with the results obtained by X-ray diffraction. The optical characteristics of the samples were determined by UV-Vis and photoluminescent spectroscopy. The aqueous solution of N-doped CDs showed a multicolor emission wavelength, in the range of 350 to 650 nm, dependent on the nitrogen-doped percentage. With increasing the nitrogen percentage, the emission spectra, depending on the excitation wavelength, have one or two peaks in the green and blue regions, which can be considered in applications such as special bioimaging and related fields. [ABSTRACT FROM AUTHOR]