Facile synthesis of tunable fluorescent carbon dots and their third-order nonlinear optical properties

• A series of CDs with tunable fluorescence emission wavelengths have been successfully synthesized.
• CDs presented tunable excitation-independent fluorescence accompanied by significant increase in intensity by simple adjustment of the concentrations.
• The third-order optical nonlinearity of CDs with different concentrations by Z-scan technique at 532 nm.

We report the synthesis and luminescent properties of carbon dots whose peak fluorescence emission are independent of excitation wavelength. Meanwhile, varying the concentrations of carbon dots can achieve a shift in the emission wavelength. Detailed structural characterization and optical properties of carbon dots with different concentrations were studied. Particularly, the blue-shifted excitation-independent emission peaks were observed when the concentration of carbon dots decreased. The decreased fluorescent properties were considered to originate from the surface modification of carbon dots. Additionally, we investigated the third-order nonlinear optical responses of carbon dots with different concentrations by Z-scan technique with single 190 fs laser pulses at 532 nm. It was found that both samples exhibited positive nonlinear refractivity and negative nonlinear absorption coefficient in the fs regime. These tunable optical properties would provide more possibilities for the utility of carbon dots in optical devices.

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