Novel solution and solid-state emissive long-wavelength carbon dots for water sensing and white LED applications

Carbon dots (CDs) are among the most popular nanomaterials due to their remarkable fluorescent and electronic properties, as well as their good biocompatibility and low cytotoxicity. Currently, CDs with aggregation-induced emission (AIE) are relatively rare and have become a significant research hotspot. This is because most conventional CDs suffer from severe quenching in a solid state. Herein, novel CDs with both solution and solid-state emissions were obtained using a facile one-step hydrothermal synthesis. Specifically, the CDs exhibit yellow solvent-dependent fluorescence in solution state (λ_em = 580 nm) and red AIE emission in solid state (λ_em = 640 nm). CDs powder is utilized as a red phosphor for light-emitting diode (LED). The resulting fabricated white LEDs (WLEDs) demonstrate good performance metrics, including a Color Rendering Index (CRI) of 89.5, Correlated Color Temperature (CCT) of 3876 K, and commission Internationale d'Éclairage (CIE) coordinates of (0.350, 0.331). Furthermore, the solvent-dependent phenomenon observed in AIE-CDs can be exploited to apply their solution as a highly sensitive fluorescence sensor for quantitatively detecting amounts of water in various organic solvents. The method offers both high accuracy and sensitivity, with R² values varying from 0.853 to 0.994 and a low detection limit ranging from 0.296 to 3.23 % across a wide linear range. This inherent versatility makes the CDs suitable for a wide range of applications, including sensing and LED devices.