Highly Bright and Stable Al-Doped Carbon Dots toward Ion and Oxytetracycline Sensors

Carbon dots (CDs) with high photoluminescence quantum yields (PLQYs) are expected to be used in sensors (e.g., metal ions and antibiotics). In this paper, aluminum-doped green-emitting CDs (M-Al-CDs) were prepared by a one-step solvothermal route using m-phenylenediamine. Al doping resulted in sample M-Al-CDs with enhanced green emission with a PLQY of 75.4% and related narrow photoluminescence (PL) spectra with a full width at half-maximum of 57 nm. The PLQYs of CDs increased by 2.3 times after Al doping. This phenomenon is ascribed to Al as a network former that can enter the carbon frameworks of CDs to affect the microstructure and PL. Highly crystalline CDs were created after Al addition, suggesting that the number of surface defects decreased and the radiation recombination efficiency increased. In addition, positive Al ions possess powerful coordination ability with the negative functional groups on the surface of CDs to further decrease nonradiational recombination, in which the Fourier transform infrared spectra of samples confirmed such interaction. Furthermore, these CDs also revealed excellent photo- and thermostability even after being stored at room temperature for 240 days. Sample M-Al-CDs exhibited a static quenching response to Cu²⁺ ions and oxytetracycline with detection limits of 0.1 and 1.0 μM, respectively. The specific detectability of M-Al-CDs for Cu²⁺ ions and oxytetracycline is related to the formation of stable complexes between M-Al-CDs and Cu²⁺ ions as well as to the interaction between Al ions and oxytetracycline. These results indicate an effective approach for the application of CDs as sensors.