Fluorescence properties of carbon dots synthesized by different solvents for pH detector

The carbon dots (CDs) are synthesized by solvothermal method with four kinds of solvents including water, dimethylformamide (DMF), ethanol and acetic acid (AA) reagent. The aqueous solutions of the CDs emit multicolor of blue (470 nm), green (500 nm), yellow (539 nm) and orange (595 nm) with dependence on the excitation wavelength, respectively. The structure, size and chemical composition of the CDs are characterized by TEM, XRD, FTIR and XPS. And the optical properties of these multicolored CDs are analyzed by UV–Vis absorption and PL spectrum. It is found that DMF and AA solvents could improve the generation of graphitic N in carbon cores and increase the COOH functional group during the synthesis of the CDs, which are the key to emit strong red fluorescence. And the COOH groups on the surface of the CDs are beneficial to the application for the determination of pH values in a strong alkaline solution.