Preparation of solid-state emissive carbon quantum dots and their integration into electroluminescent light-emitting diodes.

Carbon quantum dots (CQDs) have emerged as promising materials for electroluminescent light-emitting diodes (LEDs) because of their photostability, low toxicity and tunable luminescence. However, their implementation in solid-state devices is often hindered by aggregation-induced quenching (AIQ), which leads to a substantial loss of photoluminescence quantum yield (PLQY) and poor device reproducibility. Here, we present a robust, reproducible and scalable protocol for the preparation of solid-state emissive CQDs (SSE-CQDs) and their integration into electroluminescent LEDs. The protocol uses a solvothermal reaction between aromatic aldehydes and aromatic nitriles, involving Knoevenagel-type condensation, dehydration and carbonization. This synthetic strategy enables the formation of non-planar conjugated architectures with incorporated long-chain electron-donating alkoxy groups, which effectively suppress intermolecular π-π interactions and mitigate AIQ in the solid state. Compared with existing approaches that rely on host matrices or multistep post-synthetic modification, this protocol produces intrinsic SSE-CQDs, simplifying processing and improving reproducibility. Using this approach, SSE-CQDs with PLQYs exceeding 40% under ambient conditions can be reproducibly obtained and processed using standard solution-based techniques. This protocol describes in detail the synthesis, purification and basic optical characterization of SSE-CQDs, followed by their incorporation into electroluminescent device architectures. The complete workflow, from CQD synthesis to LED fabrication, can be completed within ~41.5 h. The procedures are compatible with conventional laboratory equipment and are suitable for researchers with experience in nanomaterial synthesis and optoelectronic device fabrication. This protocol provides a general and transferable platform for developing CQD-based solid-state emitters and LEDs.