Dual-confined carbon dots in B₂O₃ for orange-yellow room-temperature phosphorescence

Room-temperature phosphorescent (RTP) carbon dot (CDs) materials have attracted significant interest due to their excellent biocompatibility, large Stokes shift, and potential for anti-counterfeiting applications. However, the preparation of long-wavelength-emitting phosphorescent materials based on CDs remains a challenge, as most RTP CDs exhibit blue and green emissions. Here, we designed a double confinement strategy to obtain orange-yellow RTP CDs composites (CDs@B₂O₃) vis hydrothermal treatment and calcination. After calcination, the phosphorescence emission of the composite material underwent a significant red shift (546 to 582 nm). Simultaneously, under 468 nm excitation, CDs@B₂O₃-350 showed both fluorescence emission centred at 521 nm and phosphorescence emission centred at 582 and 627 nm. Structural and chemical characterizations, as well as optical studies, revealed that the CDs@B₂O₃ composite material features a highly rigid network with electron traps and stable covalent bonds, which generate multiple confinement effects. This material demonstrates great potential for application in the field of multi-level information encryption.