Solvent-free rapid synthesis of carbon nanodots at atmospheric pressure: Preparation of transparent light conversion films with ultrahigh efficient UV and blue light shielding

In this age of technology, people are inevitably surrounded by electronic devices and light-emitting devices, but the radiation generated by these devices is very harmful to humans. Therefore, it is crucial to develop a stable absorbing material with efficient absorption capacity for UV and high-energy blue light (HEBL). In this paper, we report that carbon nanodots (CDs) with strong absorption peaks in the UV and HEBL can be rapidly synthesized in large scale by simply heating urea and citric acid at high temperature under atmospheric pressure without using any solvents. Interestingly, the large-scale prepared CDs possess green fluorescence emission upon excitation in both the UV and HEBL regions, exhibiting good photoconversion ability. Furthermore, ultrahigh efficient UV and HEBL shielding films can be prepared by embedding the CDs in a carboxymethyl cellulose matrix. By characterizing their transmission and absorption spectra, it can be found that the cellulose films containing 0.2 wt% CDs achieve almost complete shielding of UV-A, UV-B, and HEBL with a guaranteed visible light (550 nm) transmission rate of 80% or above. Finally, this cellulose film was further attached to a light-emitting diode (LED) chip to investigate its practical use in the field of UV and strong blue light shielding.