Deciphering the interaction of solvents with dual emissive carbon dots: A photoluminescence study and its response for different metal ions

Carbon-based fluorescent quantum dots exhibited tunable photoluminescence (PL) property which is mainly dependent on its excitation wavelength which is an important factor required for optoelectronic and sensing applications. Here, we have established a microwave-based synthesis of dual emissive carbon quantum dots (CDs) using mixed-acid (H3PO4 + H2SO4) and mono/disaccharides as carbon precursor. In aqueous medium, CDs showed dual emission peaks at 434 nm and 518 nm, which exhibited excitation independent fluorescence property with particle size in the range of 4-7 nm. Furthermore, its photophysical properties were explored in different solvents. The astonishing bathochromic shift was observed in its emission wavelengths with the decrease in polarity of the solvents. Moreover, the metal sensing efficacy of CDs was explored in these solvent systems. It exhibited utmost selectivity for Fe(III) ions in both the organic and aqueous medium with maximum and minimum detecting limit of 1 μM and 0.4 μM respectively. These experimental results were also validated through real samples (Ferric citrate tablets 200 mg) and it showed excellent metal ion sensing accuracy for CDs in different media. The fundamental motive of this work was to explain the role of the mixed acid for the development of dual emissive CDs using a single precursor. The solvatochromic and sensing properties of CDs were explored in various solvents, which could be useful for sensing applications.