Photo-to-thermal conversion: effective utilization of futile solid-state carbon quantum dots (CQDs) for energy harvesting applications

Abstract

We report on the photo-to-thermal conversion characteristics of fluorescence-quenched solid-state carbon quantum dots (CQDs) prepared via the microwave treatment of citric acid and urea. With a fluorescence quantum yield of ∼6.98% in the aqueous dispersed form, the CQDs exhibit no photoluminescence upon solvent removal. Thus, clearly, the photoexcited electrons in the CQDs in the solid state lack a radiative de-excitation pathway, thus causing them to lose their energy non-radiatively to relax back to the ground state. Upon irradiation from a coherent, continuous-wave, monochromatic (450 nm) light source, the temperature generated by ∼0.07 mg of the solid-state carbon quantum dot sample was determined to be ∼137 °C corresponding to an intensity of ∼21.2 W cm⁻². Furthermore, its light-to-heat transduction activity was utilized for the photothermal degradation of a widely used polymer, poly(propylene carbonate), resulting in the formation of its monomer, propylene carbonate.