Photothermal evaluation of fluorescent carbon dots synthesized from vegetable oils

In this work, the thermo-optical characterization was performed on carbon dots (Cdots) synthesized using four vegetable oils as carbon sources: avocado (CdotAO), buriti (CdotBO), passion fruit (CdotPFO), and sacha inchi (CdotSIO). The Cdot-based oils with an average particle size of (8 ± 3) nm were characterized using the mode-mismatched thermal lens (TL) technique to determine thermal diffusivity (D) and the fraction of absorbed energy converted into heat (φ) at an excitation wavelength of λe = 532 nm. The thermo-optic coefficient (dn/dT) values of the green-synthesized carbon dots were measured using a Mach–Zehnder interferometric setup as a function of temperature (295–330) K. Fluorescence and time-resolved fluorescence measurements corroborate the TL measurements, and fluorescence quantum yield η (∝ (1 − φ)) values were determined. The fluorescence lifetime (τ) and η average values obtained for all Cdot-based oils are τ ≈ 3.8 ns and η ≈ 0.4, respectively. CdotPFO exhibited a higher value of η = (0.47 ± 0.03) compared with other avocado, buriti, and sacha inchi vegetable oils used in carbon dots synthesis. Carbon dots exhibited broad excitation-dependent fluorescence in the UV-visible range, and the wavelength of fluorescence in the range of (410–570) nm obtained is dependent on the carbon source used. Cdot-based oils were tested as ink markers under UV-excitation as a preliminary nanomaterial application.