Carbon dots (CDs) have attracted attention in metal‐free afterglow materials, but most CDs were heteroatom‐containing and the afterglow emissions are still limited to the short‐wavelength region. A universal approach to activate the room‐temperature phosphorescence (RTP) of both heteroatom‐free and heteroatom‐containing CDs was developed by one‐step heat treatment of CDs and boric acid (BA). The introduction of an electron‐withdrawing boron atom in composites can greatly reduce the energy gap between the singlet and triplet state; the formed glassy state can effectively protect the excited triplet states of CDs from nonradiative deactivation. A universal host for embedding CDs to achieve long‐lifetime and multi‐color (blue, green, green‐yellow and orange) RTP via a low cost, quick and facile process was developed. Based on their distinctive RTP performances, the applications of these CD‐based RTP materials in information encryption and decryption are also proposed and demonstrated.

Carbon dots (CDs) have attracted attention in metal‐free afterglow materials, but most CDs were heteroatom‐containing and the afterglow emissions are still limited to the short‐wavelength region. A universal approach to activate the room‐temperature phosphorescence (RTP) of both heteroatom‐free and heteroatom‐containing CDs was developed by one‐step heat treatment of CDs and boric acid (BA). The introduction of an electron‐withdrawing boron atom in composites can greatly reduce the energy gap between the singlet and triplet state; the formed glassy state can effectively protect the excited triplet states of CDs from nonradiative deactivation. A universal host for embedding CDs to achieve long‐lifetime and multi‐color (blue, green, green‐yellow and orange) RTP via a low cost, quick and facile process was developed. Based on their distinctive RTP performances, the applications of these CD‐based RTP materials in information encryption and decryption are also proposed and demonstrated.

Energy transfer (EnT) is a commonly used study method in the research of organic luminescent materials, but rarely reported in carbon dots (CDs) related work. In this work, an efficient EnT mediated method for enhancing room temperature phosphorescence (RTP) of CDs through embedding pure phosphorescent CDs into afterglow matrixes is brought up for the first time. In such design system, the emission intensity, phosphorescence lifetime, and emission time of CDs are prolonged significantly, and all the CD‐based materials emit more than 20 s phosphorescence visible to eye after the ultraviolet excitation. The overlap between the phosphorescence excitation spectra of CDs and the afterglow emission spectra of afterglow matrixes reveal the possibility of the EnT from matrixes to CDs, and the phosphorescence emission and lifetimes spectra of CDs, matrixes, and CDs@matrix further verify the presence of EnT process. Besides, phosphorescent CDs embedded in nonafterglow emission matrixes are also synthesized for analysis and comparison. To employ the outstanding characteristics of the compound of pure phosphorescent CDs and afterglow matrix, advanced information encryption/decryption and rapid fingerprint detection applications are designed. This EnT medicated enhancing RTP strategy provides a new design route to construct the CD‐based material with long phosphorescence emission and high emission intensity.

Room-temperature phosphorescence (RTP) with carbon dots (CDs) can be exploited further if the mechanism of trap-state-mediated triplet-state energy transfer is understood and controlled. Herein, we developed an in situ calcination method for the preparation of a CDs@ZnAl 2 O 4 composite material that exhibits unique UV and visible light-excitable ultra-broad-band RTP. The ZnAl 2 O 4 matrix can protect the triplet emissions of CDs by the confinement effect and spin−orbit coupling. In addition, benefitting from the efficient energy transfer between the inorganic trap state and the triplet state of CDs, the special yellow to red RTP of CDs@ZnAl 2 O 4 composites can be realized. A slow-decaying phosphorescence at 570 nm with a lifetime of 1.05 s and a fast-decaying phosphorescence at 400 nm with a lifetime of 0.41 s were observed with UV irradiation of 290 nm, which originated from the surface and core triplet states of CDs, respectively. Based on the unique RTP performance, anti-counterfeiting and information encryption were successfully realized using the CDs@ZnAl 2 O 4 composites with LED light or UV light.

No abstract