Investigation on synthesis and luminescent properties of red-emitting carbon dots chemically functionalized by branched-polyethylenimine

Carbon dots (C-dots) have been known as a type of important luminescent materials in the lighting field due to their advantages such as low cost, environmental benign, and broad color-tuning range. However, the C-dots often face the aggregation-induced photoluminescence quenching (AIPLQ) and film-formation instability problems, thereby causing the limitations of their application. In this work, we have prepared the C-dots with branched-polyethylenimine chemically functionalized on the particles’ surfaces. The TEM results show that the diameter of the obtained C-dots is distributed mainly in the range of 4–7 nm, with the average diameter of 5.7 nm and lattice fringe spacing of 0.19 nm related to the (100) plane. The thermogravimetry analysis reveals that the C-dots experience three stages of weight losses. The UV–Visible absorption spectra results show that there are two absorption bands at 340 nm and 505 nm in the C-dots in the form of the aqueous solution and solid-state films, which are assigned to the π–π interactions and the carbogenic core of the C-dots. In addition, the PL results reveal that the C-dots can overcome the AIPLQ and show a highly efficient red luminescence in the solid-state form, with a maximum PL quantum yield of ~ 23% under 505 nm excitation. At last, we design and achieve an excellent C-dots-based film by dealing the C-dots with a solution spin-coating method, and demonstrate the potential application of the obtained C-dots for LED device.