Vacuum-Assisted Synthesis of Solid-State Fluorescent Carbon Quantum Dots for Color Conversion LEDs.

Carbon dots (CDs) are one of the most promising nanomaterials with tunable optical properties and very good biocompatibility, opening wide perspectives in sensing, imaging, and optoelectronic applications. However, fluorescent CDs in powder form that are both adjustable and effective remain a significant issue. Here, we describe a simple, quick, and scalable process for creating solid-state green-emissive CDs using urea and trisodium citrate dihydrate with boric acid as a matrix and no dispersion solvent. The process employs a vacuum-assisted synthesis method, which enhances the molecular interaction between the precursors and ensures uniform dispersion, significantly improving the quality and stability of the final product. CDs embedded in a boric acid matrix (B-CDs) exhibit a photoluminescence quantum yield (PLQY) with a nearly 18% decrease when transitioning from aqueous solution to solid-state films. In contrast, CDs without the boric acid matrix display a significantly lower PLQY in aqueous form and no luminescence in the solid state, highlighting the enhancing effect of the boric acid matrix. By effectively reducing the aggregation-induced quenching, the boric acid matrix's spatial confinement is thought to cause this rise in fluorescence. The resulting B-CD powders exhibit adjustable CIE coordinates and have been used to fabricate color-conversion light-emitting devices on UV chips. The current study presents a viable and scalable approach to solid-state fluorescent CDs that are very stable and efficient. These CDs will find extensive potential use in luminescent devices based on CDs, ranging from flexible lighting systems to color conversion, opening a new era of possibilities.