Yellow-Emissive Carbon Dots with Long-Lifetime Room-Temperature Phosphorescence for Information Encryption and Bioimaging

Long-lifetime room-temperature phosphorescence (RTP) materials have various applications in many fields due to their long-lived emission and large signal-to-noise ratio. However, it is not easy to attain long-lifetime RTP materials owing to the spin-forbidden nature of triplet exciton transitions. Herein, yellow phosphorescence carbon-dot-based composites embedded in a MgO matrix (MgCDs) have been developed, and the lifetimes were up to 1.81 s (more than 11 s to the naked eye) in a solid state and 254 ms (more than 9 s to the naked eye) in water. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and XPS analyses were performed, and the structural characterizations indicate that carbon dots (CDs) embedded in the rigid magnesium oxide matrix restrict the vibration and rotation of CDs chromophores and suppress nonradiative recombination of triplet excitons. Further studies unveiled that the barrier effect of the insoluble MgO matrix on oxygen is likely mainly responsible for the observed long-lived RTP in water. In addition, the codoping of N, P, and Mg elements, as well as the carbonization degree, play an important role in the luminescence properties of MgCDs. Last but not least, applications in bioimaging, screen printing, anticounterfeiting, and information protection are also explored. This work offers fresh ideas for developing ultralong lifetime afterglow materials that can be applied in versatile applications.