Fig. 2: Photophysical and photothermal properties of the CDs.

a Absorption spectra of the CDs and a graphene oxide aqueous solution with the same mass concentration (200 μg mL⁻¹). b Emission spectra of CDs that are excited at various wavelengths in dilute aqueous solution that were obtained using a Horiba Jobin Yvon Fluorolog-3 spectrometer with Xenon lamp excitation. c Photothermal images of CD aqueous solutions (200 μg mL⁻¹) that were captured at various times under 655-nm laser irradiation at a power density of 1W cm⁻². d Temperature evolutions of CD aqueous solutions of various concentrations, graphene oxide aqueous solution at 50 μg mL⁻¹, and pure water under 655-nm laser irradiation at a power density of 1 W cm⁻². e Temperature evolutions of CD aqueous solutions (50 μg mL⁻¹) at various power densities. f Temperature curves of aqueous CD aqueous solution (200 μg mL⁻¹) under five cycles of photothermal heating under 655-nm laser irradiation (1 W cm⁻²)