Spatial effect and resonance energy transfer for the construction of carbon dots composites with long-lived multicolor afterglow for advanced anticounterfeiting

Carbon dots (CDs) with room-temperature phosphorescence (RTP) have attracted dramatically growing interest in optical functional materials. However, the photoluminescence mechanism of CDs is still a vital and challenging topic. In this work, we prepared CD-based RTP materials via melting boric acid with various lengths of alkyl amine compounds as precursors. The spatial effect on the structure and the RTP properties of CDs were systematically investigated. With the increase in carbon chain length, the interplanar spacing of the carbon core expands and crosslink-enhanced emission weakens, resulting in a decrease in the phosphorescence intensity and lifetimes. Meanwhile, based on triplet-to-singlet resonance energy transfer, we employed intense and long-lived phosphorescence CDs as the donor and short-lived fluorescent dyes as the acceptor to achieve long-lived multicolor afterglow. By the triplet-to-singlet resonance energy transfer, the afterglow color can change from green to orange. The afterglow lifetimes are more than 0.9 s. Thanks to the outstanding afterglow properties, the composites were used for time-resolved and multiple-color advanced anticounterfeiting. This work will promote the design of multicolor and long-lived afterglow materials and expand their applications.