Carbon quantum dots synthesized by monochromatic light driven method toward controlling optical and nonlinear optical properties

• The effect of monochromatic light on the pyrolysis synthesis of CQDs were studied. • The effect of the light irradiation was only on the surface agents of CQDs. • By increasing of the light wavelength, more citrate ions were released from CQDs. • Using light sources with longer wavelength caused a red-shift in absorption bands. • The most enhancement in nonlinear optical properties was due to the red light. In this study, carbon quantum dots (CQDs) were synthesized using pyrolysis method and monochromatic LED light sources were used to control the chemical reaction during the synthetic time. Four monochromatic LEDs with different wavelengths (violet, blue, green and red) were used in these synthetic routes. CQDs were characterized using different methods such as visible-ultraviolet spectroscopy (UV–Vis), dynamic light scattering (DLS), photoluminescence spectroscopy (PL), Fourier transform infrared (FTIR), and Transmission electron spectroscopy (TEM). According to different optical properties of the synthesized CQDs, third order nonlinear absorption coefficients of CQDs have been measured using the open aperture Z-scan technique. Experiments with close aperture Z-scan setup led only to dense patterns of diffraction rings. There was a perfect correlation between the data of all experiments where indicates the effect of monochromatic light radiation on the synthesis process is mainly on the loading of surface agents of the CQDs. With the increase in the wavelength of the irradiated light, it has been witnessed the decrease of surface agents as surface agents, the decrease of hydrodynamic diameter, increase of absorption in the visible region, increase of luminescence and its red shift, the granularity of the particles in the TEM images and increase of the nonlinear properties of the resulting nanocolloids. The present study can be a new window towards control and engineering in the synthesis of CQDs with the help of only a monochromatic light source.