Endogenetic Carbon\nDot Strategy within Melamine-Formaldehyde\nMicrospheres for Multifunctional Hybrid Fluorescence/Room-Temperature\nPhosphorescence Applications in Dry States and Aqueous Environments

Developing hybrid fluorescence (FL)/room-temperature\nphosphorescent\n(RTP) materials in dry-state, aqueous, and organic solvents holds\nparamount importance in broadening their applications. However, it\nis extremely challenging due to dissolved oxygen and solvent-assisted\nrelaxation causing RTP quenching in an aqueous environment and great\ndependence on SiO<sub>2</sub>-based materials. Herein, an efficient\nendogenetic carbon dot (CD) strategy within melamine-formaldehyde\n(MF) microspheres to activate RTP of CDs has been proposed through\nthe pyrolysis of isophthalic acid (IPA) molecules and branched-chain\nintra-microspheres. The formation mechanism of CDs@MF from molecules\nto CDs with a branched chain of microspheres has been systematically\nstudied. Detailed investigations revealed that endogenetic CDs within\nMF microspheres strongly construct covalent and hydrogen-bonded interfacial\nconnections, coupled with the protection provided by the microsphere\nshell, greatly suppressing nonradiative decay of CDs, resulting in\na yellow or orange RTP duration of about 7 s that is visible to the\nnaked eye, even in aqueous or organic environments. Three samples\nglowed bright white and orange light stemming from hybrid FL/RTP dual-mode\nemission with a quantum yield of 29%–36% and were successfully\napplied to single CD-based white and orange LEDs with tunable color\ntemperature. Additionally, the CDs@MF microspheres for water-resistant\nadvanced anticounterfeiting and time-dependent information encryption\nwere also successfully demonstrated. It provided an effective strategy\nfor multifunctional solvent-resistant FL/RTP microspheres by an endogenetic\nCD strategy.