UV luminescence stimulation in carbon dots from graphite laser ablation in ethanol and time-temperature dependences

Crystalline carbon dots (CDs) with a size on the order of 2 nm have been obtained by laser ablation of graphite in ethanol, both pure and denatured, using ns pulses at 1064 nm with a pulse energy of 100 mJ. Concentrations of CDs of the order of 10 µg/mL have been obtained by irradiating the target for 1 h at a 1 Hz repetition rate. Under UV excitation at 365 nm, CDs are luminescent, emitting a strong peak centred at approximately 473 nm. Under continuous UV excitation, the luminescence in denatured ethanol decreases nearly linearly over time, with a reduction to about 62.5% and 53.1% after 180 s at 50 °C and 0 °C, respectively. The luminescence intensity decay, during continuous UV excitation, is due to electron trapping and non-radiative recombination effects, which are influenced by time and temperature. At the CDs dispersion concentration of 72 µg/mL, the luminescence intensity returns to its maximum value after about 10 min, a metastable lifetime measured by switching off the UV excitation lamp. Spectroscopic measurements using absorbance and transmittance in the UV, visible, and IR regions, and physical characterisation of the obtained CDs dispersions were performed with reference to viscosity, refractive index, wetting ability, TEM investigations, Raman spectroscopy, and other parameters.