Solvent-Free Synthesis of Ultrabright Carbon Dots With Near-Unity Quantum Yield for High-Performance Light-Emitting Diodes.

Conventional liquid-phase syntheses of carbon dots (CDs) often involve complex solvent-precursor interactions that induce structural and spectral heterogeneities, severely limiting their optoelectronic performance. Herein, we report a highly controlled, solvent-free, single-precursor strategy utilizing 2,6-diaminonaphthalene to synthesize ultrabright, highly uniform green-emissive CDs (DAN-CDs). Through comprehensive thermal analyses and kinetic modeling, we elucidate a spatiotemporally resolved, dual-pathway formation mechanism: a nitrogen-doped core initially assembles within an oxygen-shielding autogenic precursor melt, followed by controlled, oxygen-mediated surface passivation as the melt barrier attenuates. This self-limiting oxidative capping thoroughly suppresses non-radiative structural defects. Photophysical analyses uncover an efficient intra-particle energy funneling process from the light-harvesting core to these surface traps, yielding excitation-independent green emission with a narrow bandwidth (< 60 nm) and a near-unity photoluminescence quantum yield of 91%. When integrated into self-emissive light-emitting diodes (LEDs), the devices deliver pure green electroluminescence. Notably, the peak external quantum efficiency (EQE) of 2.2% achieved herein through the solvent-free approach stands as the highest value reported to date among LEDs based on green-emissive CDs synthesized via thermal carbonization. These results conclusively underscore the strong potential of rationally designed DAN-CDs as highly efficient, environmentally benign, and heavy-metal-free emitters for next-generation optoelectronics and display applications.