Carbon Dots Exhibiting Full-Visible Tunable Emission For Light-Emitting Diode Applications

Compared with other light-emitting materials,carbon nanodots(CDs)have the advantages of low cost,easy synthesis,excellent fluorescence performance and high stability.However,the traditional CDs will have serious aggregation and cause fluorescence quenching,which hinders the application of CDs in light-emitting devices.In addition,all visible white LED usually needs a variety of different fluorescent materials as the light-emitting conversion layer,which not only increases the preparation cost,but also causes the spectral change and light-emitting drift of the device due to the inconsistent degradation time.Therefore,the research on this problem is of great significance.In this paper,a new kind of anti-aggregation quenching CDs was synthesized by microwave method,and its physical and chemical properties and luminescent characteristics were studied.A variety of monochromatic LEDs and all visible white LEDs with high color-rendering index(CRI)were successfully prepared by combining different concentrations of CDs with 405 nm LED.The main contents and achievements of this paper are as follows:1.A concentration-dependent full-visible-spectrum tunable CDs was synthesized by microwave method and characterized by TEM,XRD,XPS,FTIR,UV-Vis and PL.The results show that the prepared CDs have graphite nitrogen structure,and the surface is rich in carboxyl and hydroxyl groups and other functional groups.Its fluorescence spectrum can be tuned in the whole visible light region with the increase of concentration,that is,the fluorescence spectrum width of the CDs depends on its concentration,so that the CDs can emit different colors of fluorescence at different concentrations.2.According to the relevant characteristics of CDs,the mechanism of concentration dependence of the luminescent tunability of CDs is systematically explained.It is considered that the concentration-dependent fluorescence shift is mainly determined by the narrowing of the optical band gap(E_g)and the number of C-O-C/C-O-H groups.3.A variety of monochromatic LEDs,such as blue,cyan,green,yellow,red and dark red LEDs,and warm white and positive white LEDs with high CRI,have been successfully prepared by using the synthesized CDs of different concentrations as fluorescent conversion layers and 405 nm LED.Among them,the monochromatic LED covers 99.4%of the National Television Standards Committee(NTSC),while the warm white LED and positive white LED have CRI of 96.4 and 96.6 respectively.