Temperature-Driven Emissive Pathway Switching through Surface Chemical Evolution in Boron-Doped Carbon Quantum Dots for Sensitive Fe3+ Sensing

Boron-doped carbon quantum dots (BCQDs) exhibit attractive optical properties for sensing and bioimaging, yet the relationship between synthesis conditions, surface chemistry, and fluorescence regulation remains incompletely understood. Here, we demonstrate that the emission behavior of BCQDs can be effectively tuned through temperature-controlled solvothermal synthesis. Increasing the reaction temperature progressively suppresses the intrinsic blue emission (450 nm) while enhancing a defect-associated green emission (540 nm) without appreciably changing the particle size. Spectroscopic characterization indicates that this transition is accompanied by temperature-dependent surface chemical evolution, including increased oxygen-containing functionalities and reconstruction of heteroatom-containing surface states. Benefiting from the defect-enriched surface, BCQD200 exhibits highly selective fluorescence quenching toward Fe 3+ with a detection limit of 50 nM. Spectroscopic, temperature-dependent fluorescence, and dynamic light scattering analyses further suggest that Fe 3+ sensing involves surface coordination accompanied by charge-transfer interactions and BCQD-Fe 3+ assembly. These findings provide insights into how synthesis-controlled surface chemistry regulates the photophysical properties and sensing performance of boron-doped carbon quantum dots, offering an effective strategy for developing high-performance fluorescent nanoprobes.