Activating Room Temperature Long Afterglow of Carbon Dots via Covalent Fixation

Abstract

The achievement of long afterglow in aqueous solution and as well as with small effects of dissolved oxygen is critical for its applications, but this is still a highly difficult and challenging task. Herein, a novel strategy for facilely preparing room temperature long afterglow material is reported via covalently fixing carbon dots (CDs) onto colloidal nanosilica (nSiO 2 ). The as-obtained materials (named m-CDs@nSiO 2 ) show not only an unexpected long afterglow emission in water dispersion (lifetime as high as 0.703 s) but also with small effects of the dissolved oxygen. Further studies revealed that the observed long afterglow of m-CDs@nSiO 2 possesses a predominant delayed fluorescence nature and mixed with a portion of phosphorescence. Some key knowledge that can be concluded from this study are (i) covalent interaction could be employed as an option to fix and rigidify triplet emission species; (ii) covalent bonds fixation strategy could behave as a better alternative than that of the frequently used hydrogen/halogen bonds for stabilizing triplets, because this benefits in extending the occurrence of long afterglow from only solid to solution/dispersion forms; and (iii) the containing unsaturated bonds (e.g., CC) on the surface of CDs make them to be self-protection agents from the usual quenching effects of oxygen to the triplets due to their capabilities of reaction with oxygen during the irradiation process. On the basis of the unique long afterglow features of m-CDs@nSiO 2 in water dispersion and oxygen insensitivity, a moisture-related strategy for high-level information protection is proposed and demonstrated.

Carbon Dots‐in‐Matrix Boosting Intriguing Luminescence Properties and Applications

“…On the other hand, a unique long afterglow emission composed of TADF and phosphorescence was observed in the CDs@nSiO 2 composite . The afterglow emission spectrum of CDs@nSiO 2 was identified as its steady‐state PL spectrum, indicating the DF nature ( Figure a), and its intensity became higher under an argon atmosphere (Figure b).…”

“…Two different matrices were produced during the heating process, which were the melting recrystallized urea and biuret transformed from urea. Jiang et al reported the hydrothermal treatment of CDs in colloidal nanosilica (nSiO 2 ) solution to produce a CDs@nSiO 2 composite . The advantages of a colloidal nSiO 2 matrix such as a high water dispersibility, optical transparency, and possible coupling reaction on the surface enables CDs to fix onto colloidal nSiO 2 via strong covalent bonds.…”

“…d) Afterglow decay spectrum of CDs@nSiO 2 in water dispersion monitored at 470 nm with 365 nm excitation. Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…d) The possible emission processes of CDs@nSiO 2 . Reproduced with permission . Copyright 2017, American Chemical Society.…”

Achieving Amorphous Ultralong Room Temperature Phosphorescence by Coassembling Planar Small Organic Molecules with Polyvinyl Alcohol

“…Ultralong organic phosphorescence (UOP) at room temperature is of great importance in emission events . Some artificial systems have been developed to realize UOP through the crystal engineering, host‐guest interactions, polymer doping, and heavy atom effect . UOP is normally generated from crystal forms, since rigid crystal environment could protect the triple‐state excitation and suppress the nonradiative relaxation pathways.…”