Multi-functional ratiometric detection based on dual-emitting N-doped carbon dots

Dual-emitting N-CDs with multi-application of white light emission, detection of metal ions, solvatochromism, detection of the water content in organic solvents, pH detection, and temperature detection. [Display omitted] •Dual-emissive N-CDs were synthesized and applied for pH and temperature sensing.•Ratiometric fluorescence probe based on N-CDs detected Fe3+, Cu2+ and Ag+ simultaneously.•N-CDs exhibited unique solvatochromism phenomena and were used for detecting water content in organic solvents. Ratiometric fluorescence probes based on multi-emission carbon dots improve accuracy and sensitivity on detecting various environment issues. Herein, a novel dual-emitting N-doped carbon dots (N-CDs) was synthesized from citric acid and urea via a solvothermal method in N,N-dimethylformamide (DMF). The blue and orange emissions of N-CDs in water were modulated, and pure white light-emitting with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.33) was achieved. The two PL centers behaved differently for Fe3+, Cu2+ and Ag+ ions, with the limit of detection (LOD) of ppm as fluorescence probes. Additionally, N-CDs displayed unique solvatochromism phenomenon. A new green emission appeared in organic solvents and gradually quenched with the increase of solvent polarity. The ratiometric PL displayed an excellent linear response for detecting water, and the LOD was between 0.003 % and 0.3 % in DMF, ethanol, isopropanol and N-methylpyrrolidone. Furthermore, N-CDs exhibited pH-sensitive response in the range of 4.0–7.0 and temperature-dependent response during heating–cooling cycles between 15 and 70 °C. A simple, efficient and reliable multi-functional ratiometric probe for detecting metal ions, water content, pH and temperature simultaneously was realized. However, there is a need for future application research to overcome the limitation imposed by the excitation wavelength of 330 nm.