Carbon quantum dots synthesized by using a 405 nm laser for erosion in liquids and their applications

Photoluminescent carbon quantum dots (CQDs) have been synthesized via laser erosion of graphite targets placed in biocompatible liquids. A 405nm CW diode laser, 100 mW, has been employed to irradiate graphite in a phosphate-buffered saline (PBS) solution with water for times of 0.5–3 h. The laser erosion rate was about 10 ng/min, of which about 10% of the ablated mass consisted of synthesized CQDs. Results demonstrated that the CQDs dispersion is luminescent under UV light excitation at 365 nm. The luminescence increases with the laser irradiation time, i.e. with the concentration of CQDs in the liquid. Measurements of luminescence emission versus wavelength, UV-visible absorbance, and FTIR spectroscopy were performed. The luminescence depends on the type of solution used, the CQDs concentration and the type of surface functionalization. The produced CQDs dispersion finds interesting applications in bio-medicine, optoelectronics, UV detector, and others, as will be presented and discussed.