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

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@ZnAl2O4 composite material that exhibits unique UV and visible light-excitable ultra-broad-band RTP. The ZnAl2O4 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@ZnAl2O4 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@ZnAl2O4 composites with LED light or UV light.