Rational Synthesis of Solid‐State Ultraviolet B Emitting Carbon Dots via Acetic Acid‐Promoted Fractions of sp³ Bonding Strategy

Abstract Carbon dots (CDs) have received tremendous attention for their excellent photoluminescence (PL) properties. However, it remains a great challenge to obtain CDs with ultraviolet (UV, 200–400 nm) emission in solid state, which requires strict control of the CDs structure and overcoming the aggregation‐caused quenching (ACQ). Herein, a new sp³ compartmentalization strategy is developed to meet these requirements, by employing acetic acid to promote fractions of sp³ bonding during the synthesis of CDs. It markedly decreases the size of sp² conjugating units in the CDs, and shifts PL emission to the ultraviolet B (UVB) region (λ_max = 308 nm). Moreover, sp² domains are well spatially compartmentalized by sp³ domains and the ACQ effect is minimized, enabling the high quantum yield in solid state (20.2%, λ_ex = 265 nm) with a narrow bandwidth of 24 nm and environmental robustness. The solid‐state UVB emissive CDs are highly desired for application in photonic devices. Hence, a demo of UVB light‐emitting diodes is fabricated for plant lighting, leading to a 29% increase of ascorbic acid content in the basil. Overall, a rational and efficient way to construct solid UVB‐CDs phosphors for wide applications is provided.