Abstract
The ability of carbon dots (CDs) to emit afterglow emission in addition to fluorescence in response to UV-to-visible excitation allows them to be a new class of luminescent materials. When compared with traditional organic or inorganic afterglow materials, CDs have a set of advantages, including small size, ease of synthesis, and absence of highly toxic metal ions. In addition, high dependence of their afterglow color output on temperature, excitation wavelength, and aggregation degrees adds remarkable flexibility in the creation of multimode luminescence of CDs without the need for changing their intrinsic attributes. These characteristics make CDs particularly attractive in the fields of sensing, anticounterfeiting, and data encryption. In this review, we first describe the general attributes of afterglow CDs and their fundamental afterglow mechanism. We then highlight recent strategic advances in the generation or activation of the afterglow luminescence of CDs. Considerable emphasis is placed on the summarization of their emergent afterglow properties in response to external stimulation. We further highlight the emerging applications of afterglow CDs on the basis of their unique optical features and present the key challenges needed to be addressed before the realization of their full practical utility.
Highlights
Afterglow is an interesting optical phenomenon in which a substance releases accumulated energy in the form of photons after removal of the excitation source [1]
This review has summarized the recent advances in the field of afterglow carbon dots (CDs) ranging from physical fundamentals, afterglow activation strategy, and emergent afterglow luminescence properties to multiple applications
Improvement of the optical attributes, including efficiency and lifetime, is a fundamental challenge for afterglow CDs. Doping of heteroatoms, such as N and P, has proven effective in enhancing the probability of the occurrence of intersystem crossing into CDs to elevate the afterglow efficiency
Summary
Afterglow is an interesting optical phenomenon in which a substance releases accumulated energy in the form of photons after removal of the excitation source [1]. The ability of afterglow materials to emit long-lived emissions allows them to be distinguished from background fluorescence and to find widespread applications in the fields of lighting, bioimaging, anticounterfeiting, and optical recording [5,6,7,8,9]. When compared with other organic afterglow phosphors, CDs exhibit inherent advantages in their practical utility: (i) their main component is carbon, showing less potential toxicity and environmental concerns [21, 22]; (ii) their synthetic procedure is simple, without the need for tedious protocols and complex experimental setup; (iii) their size is small, allowing them to find applications in newly emerged nanotechnologies, such as bioimaging and printable inking [23, 24]; and (iv) their afterglow feature is tunable, permitting the creation of multiple long-lived color codes for multiplexing and information storage. We discuss the challenges and opportunities for afterglow CDs during the realization of their practical utility
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