Nitrogen-doped Carbon Quantum Dot And Its Luminescent Properties

Carbon quantum dots (CNDs) are quasi spherical nanoparticles below 10 nm with the feature of superiority in water solubility, chemical interness, low toxicity, ease of functionalization and resistance to photobleaching. Also to be referred as "fluorescent carbon quantum dots", CNDs have shown strong fluorescence emission as well as the photoinduced electron transfer properties. Those have been established considerable applications, such as biomedicine, optoelectronic devices. Recently, the ions doped or size-controlled functional CNDs were demonstrated to be suitable for organic light-emitting diode (OLED), photovoltaic device and biomedical images. In this paper, nitrogen-doped CNDs were synthesised by chemical method. The growth mechanisms and luminescence properties were discussed. The main results are as follows:(1) We have synthesized nitrogen-doped carbon quantum dots (N-CNDs) by using precursors of citric acid (CA) and 1-octadecylamine (C18H38N, ODA) in the noncoordinating solvent of octadecene (ODE). The formation mechanism was discussed and described. The long-chain molecules having amide functional groups were formed by dehydration process from the CA and ODA and acted as precursors. Under high temperature, they gradually converted to interchain imide bonds and then to the carbonaceous core by aggregation and decomposition. With intensified consumption of alkane chain attached to the carbonaceous core, the final N-CNDs products were obtained. We also verified the formation mechanism by investigating the temperature influence on the feature of N-CNDs. Under the elevated temperature, the decrease in particle size and the red-shift in PL spectra were observed with the nitrogen content enhancement. Finally, a monolayer LED (ITO/N-CNDs(300℃)/Al) was fabricated by using N-CNDs as active layer.(2) The effect of various kinds of carbon sources on the optical properties of N-CNDs was investigated. By using spectroscopic measurements, the growth mechemism for N-CNDs under various precursors, including organic amines with different chain length or different carbon sources, were comparatively discussed. The conclusion was reached that precursors with shorter chain were intended to get small-sized samples as well as high nitrogen content. It suggested an approach to get the emission-tunable CNDs.