Carbon nitride dots (CNDs) emerge as a metal-free luminescent material combining earth-abundant precursors, exceptional chemical stability, and tailorable optoelectronic properties. Here we report a solvent-free synthesis of CNDs through thermal polymerization method that achieves unprecedented photoluminescence quantum yields of 72% alongside balanced charge transport characteristics. The CNDs exhibit uniform size distribution and excellent colloidal stability in various solvents. Leveraging these advantages, we demonstrate a solution-processed light-emitting diodes (LED) using CNDs as the emissive layer, with a luminance exceeding 1000 cd·m⁻² for the first time and a record external quantum efficiency of 0.9% among CNDs-based electroluminescent devices. Our work establishes solution-processable CNDs as promising candidates for low-cost, environmentally benign light-emitting technologies.