Bridging-Carbon Reconstruction of π Conjugation Enables Bright Blue Emission from Crystalline Carbon Nitride Quantum Dots

Abstract Triclinic crystalline carbon nitride (CCN) quantum dots are promising metal-free blue emitters, but their luminescence is limited by residual alkali ions, framework defects, and surface-mediated nonradiative decay. Here we develop a bridging-carbon reconstruction strategy to produce few-layer CCN quantum dots (C-CCNQDs) through reactive-salt polymerization followed by alkali-assisted solvothermal exfoliation. Bridging-carbon units connect adjacent heptazine motifs and extend π-electron delocalization, while amino and hydroxyl groups formed during exfoliation passivate surface dangling bonds. The combined framework reconstruction and surface passivation redirect excited-state relaxation from defect-dominated pathways toward framework-centered radiative recombination. The resulting C-CCNQDs exhibit sky-blue emission at 470 nm, a photoluminescence quantum yield of 65.4%, and substantially enhanced photostability. As a proof of concept, C-CCNQD light-emitting diodes show spectrally stable electroluminescence at 470 nm with a maximum external quantum efficiency of 1.47%. These findings establish atomic reconstruction of π-conjugated carbon nitride frameworks as a route to bright, metal-free blue-emitting quantum dots.