A Facile Preparation of Multicolor Carbon Dots.

Carbon dots (CDs) have raised broad interest because of their great potential in the fluorescence related fields, such as photocatalysis and bioimaging. CDs exhibit different optical properties when dissolved in various solvents. However, the effects of solvents during the process of preparation on the fluorescence emission of CDs are still unclear. In this work, CDs were prepared by a simple one-pot solvothermal route. Typical critic acid and thiourea were used as precursors. Through changing the volume ratio of water to N,N-dimethylformamide (DMF), we have obtained color tunable CDs, with the emission wavelength from 450 to 640 nm. TEM images, Raman and XPS spectra indicate that the particle size of CDs and the content of surface functional groups (C-N/C-S and C≡N bonds) increase with the increasing ratio of DMF to water, which results in the optimal emission wavelength red-shifted. The prepared multicolor CDs may have prospects in the lighting applications.

Yu R ，Liang S ，Ru Y ，Li L ，Wang Z ，Chen J ，Chen L ... -  《-》

Multicolor Luminescent Carbon Dots: Tunable Photoluminescence, Excellent Stability, and Their Application in Light-Emitting Diodes.

Rao L ，Zhang Q ，Sun B ，Wen M ，Zhang J ，Zhong G ，Fu T ，Niu X ... -  《Nanomaterials》

Solvent Effects on Fluorescence Properties of Carbon Dots: Implications for Multicolor Imaging.

Carbon dots (CDs) are synthesized by the solvothermal method with four kinds of solvents including water, dimethylformamide (DMF), ethanol, and acetic acid (AA). The aqueous solutions of the above CDs emit multiple colors of blue (470 nm), green (500 nm), yellow (539 nm), and orange (595 nm). The structures, sizes, and chemical composition of the CDs are characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The optical properties of multicolored CDs are analyzed by UV-vis absorption and photoluminescence (PL) spectra. It has been revealed that DMF is the key solvent to synthesized CDs for the red shift of fluorescence emission, which could be enhanced by adding an AA solvent. The structures of functional groups such as the contents of graphitic N in carbon cores and oxygen-containing functional groups on the surface of CDs are affected by these four solvents. According to the oxidation and selective reduction of NaBH4, the implication for multicolor imaging has been discussed based on the COOH, C-O-C, and C=O functional groups.

Huo X ，Shen H ，Liu R ，Shao J ... -  《ACS Omega》

Solvent-Controlled Synthesis of Highly Luminescent Carbon Dots with a Wide Color Gamut and Narrowed Emission Peak Widths.

Carbon dots (CDs) have tremendous potential applications in bioimaging, biomedicine, and optoelectronics. By far, it is still difficult to produce photoluminescence (PL) tunable CDs with high quantum yield (QY) across the entire visible spectrum and narrow the emission peak widths of CDs close to those of typical quantum dots. In this work, a series of CDs with tunable emission from 443 to 745 nm, quantum yield within 13-54%, and narrowed full width at half maximum (FWHM) from 108 to 55 nm, are obtained by only adjusting the reaction solvents in a one-pot solvothermal route. The distinct optical features of these CDs are based on their differences in the particle size, and the content of graphitic nitrogen and oxygen-containing functional groups, which can be modulated by controlling the dehydration and carbonization processes during solvothermal reactions. Blue, green, yellow, red, and even pure white light emitting films (Commission Internationale de L'Eclairage (CIE)= 0.33, 0.33, QY = 39%) are prepared by dispersing one or three kinds of CDs into polyvinyl alcohol with appropriate ratios. The near-infrared emissive CDs are excellent fluorescent probes for both in vitro and in vivo bioimaging because of their high QY in water, long-term stability, and low cytotoxicity.

Ding H ，Wei JS ，Zhang P ，Zhou ZY ，Gao QY ，Xiong HM ... -  《-》

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, -NH2, 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.

Su R ，Guan Q ，Cai W ，Yang W ，Xu Q ，Guo Y ，Zhang L ，Fei L ，Xu M ... -  《RSC Advances》