Cross‐linking enhanced room‐temperature phosphorescence of carbon dots

Abstract

Currently, there is a strong drive to discover alternative materials that exhibit room-temperature phosphorescence (RTP) for displays, bioimaging, and data security. Ideally, these materials should be nontoxic, cheap, and possess controllable photoluminescent properties. Carbon dots (CDs) possess each of these characteristics, but to date, less attention has been paid to their RTP mechanism. Herein, we synthesized a series of CDs by self-crosslinking and carbonization of precursor. The resultant CDs were luminescent and exhibited a bright, micro-second afterglow lifetime. To increase the RTP, a second microwave processing step was used to coat the CDs with polyvinyl alcohol (PVA), polyacrylamide (PAM), or tetraethyl orthosilicate (TEOS), producing CDs@PVA, CDs@PAM, and CDs@TEOS composites. The core-shell structure acted to enhance crosslinking at the surface of the CDs to boost the RTP, creating abundant energy levels for intersystem crossover. In situ X-ray photoelectron spectroscopy verified electron transfer during luminescence. Finally, we present a design rule that can be used to tune the quantum yields and RTP lifetime of CDs, based on the effective stabilization of triplet excited states through the extent and strength of cross-linking. This simple strategy provides a flexible route for guiding the further development of CDs with tailored RTP properties for various applications.

Aggregation in carbon dots

“…Reproduced with permission. [108] Copyright 2022, Wiley-VCH π−π stacking. [93] In CDs, phenomena similar to AIE have been reported, specifically aggregation-induced fluorescence enhancement and aggregation-induced wavelength-redshifts.…”

“…Phosphorescence is more difficult to produce than fluorescence because it involves a triplet exciton transition and is spinforbidden. [108,109] At room temperature, the long lifetime of the triplet excitons means they are easily dissipated by nonradiative decay processes. [110,111] In order to produce phosphorescence, efficient intersystem crossing and suppression of nonradiative transitions are necessary.…”

“…Likewise, inspired by the concept of CEE. Wang et al [ 108 ] prepared CPDs with room temperature phosphorescence by self‐crosslinking and carbonization (Figure 6G). The results showed that the strength and degree of crosslinking regulated the RTP of CPDs, with the tighter crosslinking, the Δ E ST decreased and the phosphorescence emission enhanced.…”

Aggregation in carbon dots

“…Likewise, inspired by the concept of CEE. Wang et al [107] prepared CPDs with room temperature phosphorescence by self-crosslinking and carbonization (Figure 6G). The core-shell structure of CPDs enhanced the crosslinking of CPDs and boosted the phosphorescence, creating rich energy levels for intersystem crossover.…”

Enhanced Aggregation-Induced Phosphorescence of Carbon Dots for Information Encryption Applications

“…In recent years, large attention has been paid to room-temperature phosphorescent (RTP) materials due to their excellent characteristics, such as large Stokes shift, long afterglow lifetime, and effective elimination of background fluorescence. − These characteristics endow them with wide application prospects in information security, photoelectronics, sensing, and high-sensitivity bioimaging. − At present, common RTP materials still have the shortcomings of biotoxicity, environmental hazard, and high synthesis cost. − To improve the situation, carbon dots (CDs) as a potential candidate material have become one type of the next-generation RTP materials. , …”