Multicolor Graphene Quantum Dots via Solvatochromic Tuning and Sulfur Doping for Light-Emitting Diodes

Recently, graphene quantum dots (GQDs) with polychrome emission capability have attracted much attention due to their multifarious applications. In this study, we report a facile and green approach for rapid preparation of multicolor emission GQDs. Experimentally, UV light was used to drive the low-temperature synthesis, and a tunable emission wavelength of the GQDs was achieved through the synergistic effect of solvatochromic tuning and sulfur doping. Results show that multicolor emission wavelengths of green-GQDs (G-GQDs) from blue to yellow are obtained by simply controlling the polarity of the surrounding solutions. Moreover, red-GQDs with the emission wavelengths extended from green to red are further obtained by sulfur doping. Thereafter, G-GQDs were used to develop a trace water-detecting platform, ascribed to the high sensitivity of water-quenchable fluorescence, and a low detection limit of 0.061% was achieved. Meanwhile, based on the outstanding multicolor tunability of as-prepared GQDs, we successfully manufactured multicolor solid fluorescence films to fabricate multicolor light-emitting diode (LED) devices. Furthermore, high-quality white LEDs (WLEDs) are fabricated with the CIE coordinates of (0.341, 0.354) and a color temperature of 5161 K. This study highlights the potential of GQDs in various applications, including solid-state fluorescence films, optoelectronics, and optical molecular sensing.