Tunable Matrix-Free Solid-State Multi-Color Carbon Dots via Solvothermal Reaction for Light-Emitting Devices and Latent Fingerprint Applications

Solid-state multicolor carbon dots (SMCDs) are a class of fascinating luminescent nanomaterials that hold great potential for various applications, such as optoelectronic devices, biosensing, and anticounterfeiting. However, SMCDs easily suffer from fluorescence quenching due to π−π stacking. Adding a matrix into CDs may alleviate this problem, but it results in complex preparation, poor repeatability and stability, and weak fluorescence. Therefore, it is urgent to develop matrix-free SMCDs with high performance. In this study, a simple class of SMCDs without incorporating a matrix was prepared via a solvothermal method. The emission color can be adjusted from green to red by using different precursors and solvents. The detailed study shows that the aggregation-induced emission (AIE) effect originates from a hydrogen-bond network formed by the amide functional groups of SMCDs, inhibiting π−π stacking. Meanwhile, sp2-conjugated domains and graphitic nitrogen content play an important role in controlling fluorescence color. In addition, matrix-free SMCDs were successfully applied in light-emitting diodes (LEDs) and latent fingerprints (LFPs) with three levels of detail. This study provides an effective strategy to prepare matrix-free solid MCDs and demonstrates their potential applications in solid-state light-emitting devices and latent fingerprint detection.