Multiemissive Room-Temperature Phosphorescent Carbon Dots@ZnAl₂O₄ Composites by Inorganic Defect Triplet-State Energy Transfer

Abstract

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.

Multicolor-Emissive Carbon Dots for White-Light-Emitting Diodes and Room-Temperature Phosphorescence

“…Room-temperature phosphorescence (RTP) materials have been applied as sensors, photocatalysts, and optoelectronics and in security protection. , CDs-based RTP materials have drawn much attention because of their low-cost production and unique physicochemical properties. A RTP based on CDs has been developed by embedding the CDs in rigid matrixes like polymers, melamine, zeolites, etc., through hydrogen bonding, chemical bonding, and the formation of a confined structure. − To date, various organic molecules have been used for the synthesis of CDs-based RTP materials. − For example, Zhu et al prepared CDs from citric acid and urea. Further, they stated that the nitrogen-containing groups H-bond and protect the excited triplet state .…”

Multiple Stimuli‐Response Polychromatic Carbon Dots for Advanced Information Encryption and Safety

“…One flower pattern that possesses red petals and green leaves is found after removal of W‐LED and UV stimulations. [ 63 ]…”

“…For instance, by embedding CDs into the hydrotalcites coupled with the Zn 2+ ion and the ZnAl 2 O 4 host, RTP emission with long lifetime and high QYs are achieved because efficient energy transfer process occurs between the trap state of inorganic matrixes and the triplet states of CDs. [63,75] For polymers, abundant hydrogen bonds can be shared with the surface functional groups of CDs and further rigidify CDs, thereby boosting the electronic transition of the subfluorescent groups of CDs. Among various polymers, PVA is commonly used and excellent RTP properties are obtained.…”

Facile Synthesis of Multi-Emission Nitrogen/Boron Co-Doped Carbon Dots from Lignin for Anti-Counterfeiting Printing

“…To address the above challenge, the multi-emission CD anti-counterfeiting materials have been developed for achieving multiple kinds of fluorescence in a single security label by changing stimuli factors, thus realizing advanced multi-level optical anti-counterfeiting [ 9 , 10 , 11 ]. Wang et al [ 12 ] prepared dual-emission CDs with yellow/orange fluorescence from phloroglucinol dihydrate, boric acid and ethylenediamine by a one-step microwave method, which exhibited a high solid-state fluorescence QY of 39.0%.…”