Carbon Dot/Al<sub>2</sub>O<sub>3</sub> Nanocomposites with an Enhanced Lifetime, Phosphorescence Quantum Efficiency, and Stability for Anticounterfeiting Applications
Guanyu Li, Ruonan Jia, Zheng Liu, Tianfei Qi, Xuefeng Wei, Xin Xu, Linbo Zhang, Liangjun Yin, Wang Li
Abstract
A short lifetime, low phosphorescence quantum efficiency (PQE), and unstable room-temperature phosphorescence (RTP) in oxidants and solvents are the core problems in the development of carbon dot (CD)-based RTP materials for anticounterfeiting applications. Herein, a series of CDs/Al 2 O 3 nanocomposites with excitation-dependent RTP properties were fabricated by a sol–gel process followed by high-temperature treatment. The crystalline structure and rigid Al–O network of the Al 2 O 3 matrix could readily benefit the stabilization of the triplet excited state of CDs. The Al–O–C interactions between the CDs and Al 2 O 3 favor the facilitation of intersystem crossing (ISC) to effectively populate triplet excitons, which contributes to the RTP with a low energy gap. As a result, an ultralong lifetime of up to 1.4 s (observed by the naked eye for 22 s) and a high PQE of 12.78% were achieved by CDs/Al 2 O 3 -500 and CDs/Al 2 O 3 -300, respectively. The results demonstrated that the oxidants, polar solvents, and strong acids and alkalis almost had no effect on the RTP emission of the CDs/Al 2 O 3 nanocomposites. Taking advantage of the ultralong phosphorescence afterglow, excitation-dependent multicolor RTP emission, and excellent stability, graphics of the Eight Trigrams were present for advanced anticounterfeiting via time-resolved luminescence imaging based on different CDs/Al 2 O 3 nanocomposites.