Amorphous B-doped graphitic carbon nitride quantum dots with high photoluminescence quantum yield of near 90% and their sensitive detection of Fe2+/Cd2+

Graphitic carbon nitride quantum dots (CNQDs) are emerging as attractive photoluminescent (PL) materials with excellent application potential in fluorescence imaging and heavy-metal ion detection. However, three limitations, namely, low quantum yields (QYs), self-quenching, and excitation-dependent PL emission behaviors, severely impede the commercial applications of crystalline CNQDs. Here we address these three challenges by synthesizing boron-doped amorphous CNQDs via a hydrothermal process followed by the top-down cutting approach. Structural disorder endows the amorphous boron-doped CNQDs (B-CNQDs) with superior elastic strain performance over a wide range of pH values, thus effectively promoting mass transport and reducing exciton quenching. Boron as a dopant could fine-tune the electronic structure and emission properties of the PL material to achieve excitation-independent emission via the formation of uniform boron states. As a result, the amorphous B-CNQDs show unprecedented fluorescent stability (i.e., no obvious fading after two years) and a high QY of 87.4%; these values indicate that the quantum dots obtained are very promising fluorescent materials. Moreover, the B-CNQDs show bright-blue fluorescence under ultraviolet excitation when applied as ink on commercially available paper and are capable of the selective and sensitive detection of Fe2+ and Cd2+ in the parts-per-billion range. This work presents a novel avenue and scientific insights on amorphous carbon-based fluorescent materials for photoelectrical devices and sensors.