Fe ion derived bright green photoluminescence from red-emitting carbon dots and their concentration and pH dependence

The development of self-colorimetric probes for Fe 3+ detection without external reference remains a significant challenge, despite its critical importance in environmental monitoring and disease diagnosis. In this paper, bright red-emitting carbon dots (r-CDs) with photoluminescence (PL) quantum yield of 35.8 % were synthesized via a one-step solvothermal strategy. The abundant surface hydroxyl/carboxyl groups of r-CDs enabled specific Fe 3+ ion coordination resulted in a novel PL phenomenon, in which the red emitting (650 nm) of the r-CDs changed into green-emitting (500 nm) because of new fluorescent centers formation. pH stability test confirmed the robustness of r-CDs forFe 3+ sensing in a pH region of 2–13.This phenomenon is ascribed to a dual-mode self-colorimetric sensing platform, achieving a detection limit of 10.7 nM and a wide linear range of 0–700 μM in solution. Experimental result confirmed that Fe 3+ coordination triggered electron transfer and lead to new emitting center generation. This bright green emitting was also observed once r-CDs were added a SiO 2 gel with Fe ions, suggesting a significant application in solid-state moist environmental. This novel PL phenomenon is crucial for the preparation and application of CDs.