Synthesis of Good Solid‐State Emissive Carbon Dots through Microwave‐Assisted Microemulsion Process

Environmental‐friendly carbon dots (CDs) have found wide applications in the fields of white light emitting diode (WLED), chemical sensor, wide‐gamut display, etc. However, for the aggregation‐caused quenching (ACQ) effect, high dose of CDs immobilization generally suffers from the great fluorescence quenching, hindering their practical uses in many cases. In the present work, a one‐step microwave‐assisted microemulsion process is developed to prepare matrix‐free green CDs powders with absolute fluorescent quantum yield (QY) up to 48.34%. From dilute solution to matrix‐free powder, the QY of CDs decreases only about 20%, significant smaller than the sample prepared without surfactant (74%). Structural characterization and fluorescent lifetime measurements suggest that the passivation of hydrophobic long‐alkyl chains from surfactant Span‐80 is very key for their good solid‐state photoluminescence (PL). For the good solid‐state PL and various solvent‐compatibility, the CDs reported show promising applications in the fabrication of WLED and the measurement of water content of ethanol/water solution. This work provides a new idea to design and simply synthesize desirable CDs‐based luminescent materials with good solid‐state PL.