In recent years, carbon dots (CDs), including carbon nanodots, carbonized polymer dots, carbon quantum dots, and graphene quantum dots have attracted a mounting interest as readily accessible, nontoxic, and relatively inexpensive carbon-based nanomaterials. Yet, despite intense research for a number of years, a unifying picture is still lacking to clarify the exact definition, clear chemical structure, and unique optical properties of this family of nanomaterials. In this review, we systematically summarize the recent development of CDs from molecular design to related properties of excited states as well as their applications in optoelectronic devices and biology. We point out the current challenges, including exploring precise synthesis, clarifying the structure-property relationship, and regulating singlet and triplet states of fluorescence, phosphorescence, and delayed fluorescence. Moreover, the structural optimization of optoelectronic devices, tumor targeting mechanism, selective imaging, and drug delivery of CDs are also highlighted. We hope that the information provided in this review will inspire more exciting research on CDs from a brand-new perspective and promote practical application of CDs in multiple directions of current and future research.

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Featuring a combination of size-tunable emission wavelengths, high thermal stability, and low cytotoxicity, carbon quantum dots (CQDs) have opened up a new possibility for next-generation displays.

Carbon dots (CDs), as emerging carbon nanomaterials, have been regarded as promising alternatives for electroluminescent light‐emitting diodes (LEDs) owing to their distinct characteristics, such as low toxicity, tuneable photoluminescence, and good photostability. In the last few years, despite remarkable progress achieved in CD‐based LEDs, their device performance is still inferior to that of well‐developed organic, heavy‐metal‐based QDs, and perovskite LEDs. To better exploit LED applications and boost device performance, in this review, a comprehensive overview of currently explored CDs is presented, focusing on their key optical characteristics, which are closely related to the structural design of CDs from their carbon core to surface modifications, and to macroscopic structural engineering, including the embedding of CDs in the matrix or spatial arrangement of CDs. The design of CD‐based LEDs for display and lighting applications based on the fluorescence, phosphorescence, and delayed fluorescence emission of CDs is also highlighted. Finally, it is concluded with a discussion regarding the key challenges and plausible prospects in this field. It is hoped that this review inspires more extensive research on CDs from a new perspective and promotes practical applications of CD‐based LEDs in multiple directions of current and future research.

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