Microplasma-assisted synthesis and regulation the luminescence performance of glucose-based carbon dots by sodium borohydride

The effect of sodium borohydride (NaBH₄) on the luminescent properties of glucose-based carbon dots synthesized by the plasma method is investigated. The spectral and kinetic properties of the carbon dots were studied using a MicroTime 200 confocal scanning fluorescence microscope. The lower concentration limit of NaBH₄ was established at which there is an enhancement of the CDs luminescence intensity. It was found that adding of sodium borohydride to the CDs solution at concentration below 2.5 mg/mL leads to an increase in the luminescence intensity, while a decrease in intensity is noted at concentrations above 2.5 mg/mL. Enhancement of the luminescence intensity by 2.8 times was detected for the sample with the mass fraction of NaBH₄ was 0.04 % in the solution. Using the time-correlated photon counting method, it was shown that the luminescence decay kinetics is described by a tri-exponential function. It has been experimentally demonstrated that the fast luminescence time component is related to the carbonyl functional group on the carbon dots surface.