Generating triplet states in carbon quantum dots confined in mesoporous MgO for phosphorescence and photocatalysis applications

In this study, room-temperature phosphorescence (RTP) was observed from carbon quantum dots (CQDs), which were embedded in porous magnesium oxide (MgO) via the high-temperature pyrolysis of citric acid (CA) and Mg₂(OH)₂CO₃. The mesoporous MgO confined the CQDs via oxygen-containing groups and through changes in the angular momentum of surface atoms. Then, triplet states were created and the MgO-CQDs hybridization showed a typical excitation-dependent phenomenon, wherein fluorescence and RTP were red shifted when the excitation wavelength shifted to a longer wavelength, rendering an anticounterfeiting application. Moreover, the pyrolysis of CA in MgO resulted in a high specific surface area and extended the absorption wavelength range. Accompanied with the enhanced charge separation induced by delayed recombination of electrons and holes in the surface triplet state of CQDs, hybridization revealed an improved photocatalytic capability to degrade organic pollutants compared with pure MgO and its hybridization of CQDs without the Mg₂(OH)₂CO₃ precursor.