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

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.