High‐Efficiency Solid‐State Luminescence from Hydrophilic Carbon Dots with Aggregation‐Induced Emission Characteristics

Abstract Carbon dots (CDs) have excellent properties and have made great progress in synthesis and applications. However, it is still a challenge to realize convenient preparation and highly emissive solid‐state luminescence without the assistance of matrix. In this study, high‐efficiency hydrophilic yellow emissive CDs (Y‐CDs) with aggregation‐induced emission (AIE) characteristics are synthesized by a one‐pot microwave method. Y‐CDs show weak yellow emission with a photoluminescence quantum yield (PLQY) of 6.14% in aqueous solutions, but exhibit a significantly enhanced PLQY of 58.35% in the solid state. The AIE characteristic is confirmed by the phenomenon that the fluorescence emission intensity of Y‐CDs continues to increase with the gradual increase of the poor solvent fraction. The AIE phenomenon of Y‐CDs is derived from the suppression of surface piperazine groups motions and decrease of the non‐radiative rate, as is verified by a series of experiments. Finally, based on the high PLQY and AIE property, Y‐CDs are applied as a color‐converting layer on blue‐light‐emitting chips to fabricate white‐light‐emitting diodes with color coordinates of (0.31, 0.35), while Y‐CDs are also explored for their potential applications in anti‐counterfeiting, encryption and bioimaging.