Lanthanum-doped carbon quantum dots (La-CQDs) for detection of Fe3+ in colorimetric test paper and information anti-counterfeiting

Based on the fluorescence quenching principle, a novel lanthanum-doped carbon quantum dots (La-CQDs) fluorescence probe was successfully developed for ion detection of Fe3+. La-CQDs with a fluorescence quantum yield of 29.93% was prepared in ethanol solution using ammonium citrate as the carbon source and lanthanum nitrate as the dopant. The luminescence performance of La-CQDs was enhanced by La doping and maintained over 90% of the maximum fluorescence intensity in different anions, water content and organic solvent environments. In the range of 25–200 μM, the fluorescence intensity of La-CQDs displayed a good linear relationship (Y = 0.00675X+ 1.07679, R2 = 0.9888) with the concentration of Fe3+ and its limit of detection (LOD) was calculated to be 6.78 μM. The method was successfully applied to the detection of Fe3+ in green tea and the measurement error was less than 3%. In addition, La-CQDs was developed for fluorescent colorimetric test paper and information anti-counterfeiting, while the fluorescence quenching effect was observed intuitively on the paper.