Endogenetic Carbon Dot Strategy within Melamine-Formaldehyde Microspheres for Multifunctional Hybrid Fluorescence/Room-Temperature Phosphorescence Applications in Dry States and Aqueous Environments

Developing hybrid fluorescence (FL)/room-temperature phosphorescent (RTP) materials in dry-state, aqueous, and organic solvents holds paramount importance in broadening their applications. However, it is extremely challenging due to dissolved oxygen and solvent-assisted relaxation causing RTP quenching in an aqueous environment and great dependence on SiO₂-based materials. Herein, an efficient endogenetic carbon dot (CD) strategy within melamine-formaldehyde (MF) microspheres to activate RTP of CDs has been proposed through the pyrolysis of isophthalic acid (IPA) molecules and branched-chain intra-microspheres. The formation mechanism of CDs@MF from molecules to CDs with a branched chain of microspheres has been systematically studied. Detailed investigations revealed that endogenetic CDs within MF microspheres strongly construct covalent and hydrogen-bonded interfacial connections, coupled with the protection provided by the microsphere shell, greatly suppressing nonradiative decay of CDs, resulting in a yellow or orange RTP duration of about 7 s that is visible to the naked eye, even in aqueous or organic environments. Three samples glowed bright white and orange light stemming from hybrid FL/RTP dual-mode emission with a quantum yield of 29%-36% and were successfully applied to single CD-based white and orange LEDs with tunable color temperature. Additionally, the CDs@MF microspheres for water-resistant advanced anticounterfeiting and time-dependent information encryption were also successfully demonstrated. It provided an effective strategy for multifunctional solvent-resistant FL/RTP microspheres by an endogenetic CD strategy.