Gram-scale synthesis of aggregation-caused quenching-resistant red-emissive carbon dots for potential applications

Abstract

Recently, red fluorescent carbon dots (CDs) have shown great potential in diverse applications. It is found that red fluorescence properties are maintained in the liquid state, while in solidification, their fluorescence decreases or vanishes, either through the aggregation-caused quenching (ACQ) effect or the surface modification phenomenon. As a result, CDs have been extremely limited for solid-state phosphor applications such as fabricating white light-emitting diodes (WLEDs). However, developing CDs with immense fluorescence intensity and stability in both solid and liquid states remains a significant challenge. The present work describes a one-step thermal carbonization process for the generation of CDs with red emission. Interestingly, the synthesized carbon dots are red fluorescent in the solid state and retain their fluorescence in the liquid state. Here, it is demonstrated that bright red fluorescence emission is triggered by n–π* transitions generated by CN/CO/CS groups, and red-shifted emission is caused by greater amounts of nitrogen and sulfur introduced/co-doping, particularly the graphitic N of carbon dots. The red-emissive CDs were implemented in developing fluorescent polymeric films, which were then used for WLED devices. Their correlated color temperature (CCT) was 4033 K, and their color-rendering index (CRI) was 96. Surprisingly, the as-synthesized CDs exhibited room-temperature phosphorescence (RTP), encouraging us to utilize the CDs for anticounterfeiting. Furthermore, we demonstrated the practical suitability of the synthesized CDs in bioimaging and fluorescent ink due to their excellent water solubility.