Ultra‐strong phosphorescence with 48% quantum yield from grinding treated thermal annealed carbon dots and boric acid composite

Abstract

Metal-free room-temperature phosphorescence (RTP) materials are of great significance for many applications; however, they usually exhibit low efficiency and weak intensity. This article reports a new strategy for the preparation of a high-efficiency and strong RTP materials from crystalline thermal-annealed carbon dots (CDs) and boric acid (BA) composite (g-t-CD@BA) through grinding-induced amorphous to crystallization transition. Amorphous thermal-annealed CDs and BA composite (t-CD@BA) is prepared following a thermal melting and super-cooling route, where the CDs are fully dispersed in molten BA liquid and uniformly frozen in an amorphous thermal annealed BA matrix after super-cooling to room temperature. Upon grinding treatment, the fracture and fragmentation caused by grinding promote the transformation of the high-energy amorphous state to the lower energy crystalline counterparts. As a result, the CDs are uniformly in situ embedded in the BA crystal matrix. This method affords maximum uniform embedding of the CDs in the BA crystals, decreases nonradiative decay, and promotes intersystem crossing by restraining the free vibration of the CDs, thus producing strong RTP materials with the highest reported phosphorescence quantum yield (48%). Remarkably, RTP from g-t-CD@BA powder is strong enough to illuminate items with a delay time exceeding 9 s.

Cross‐linking enhanced room‐temperature phosphorescence of carbon dots

“…44 Between 250°C and 400°C, all samples showed a large mass loss associated with the degradation of surface polymers or organic groups. 40 The mass losses observed for the composites were smaller than those for the pristine CDs, suggesting that the surface modification (i.e., additional cross-links arising from the core-shell structure of the composites) improved the thermal stability of CDs.…”

“…All samples showed an observed weight loss of more than 10% on heating from room temperature and 150°C, which can be attributed mainly to the loss of physically and chemically adsorbed water and also possibly the loss of some small volatile compounds (Figure 1I). 44 Between 250°C and 400°C, all samples showed a large mass loss associated with the degradation of surface polymers or organic groups 40 . The mass losses observed for the composites were smaller than those for the pristine CDs, suggesting that the surface modification (i.e., additional cross‐links arising from the core–shell structure of the composites) improved the thermal stability of CDs.…”

“…PVA, PAM, and TEOS contain numerous functional groups such as amino, hydroxyl, and ethoxy, which acted to enhance spin-orbit coupling by improving the ISC from singlet-totriplet excited states in the CDs for generating the triplet excitons but also restrict CDs motion by extending the crosslinking network (i.e., through bonding between surface groups of the CDs surrounding polymer shell) and suppressing the nonradiative decay of excited triplet state. 40 At the same time, the number of functional groups and side chains will produce different cross-linking structures. Furthermore, the formation of the core-shell system may have acted to enhance the rigidity of the polymer matrix for generating long-lived RTP emissions under ambient conditions.…”

“…To further adjust the RTP emission properties of the CDs, we coated the CDs with shells of cross‐linked PVA, PAM, or TEOS via a second microwave processing step (Figure 1A). PVA, PAM, and TEOS contain numerous functional groups such as amino, hydroxyl, and ethoxy, which acted to enhance spin‐orbit coupling by improving the ISC from singlet‐to‐triplet excited states in the CDs for generating the triplet excitons but also restrict CDs motion by extending the crosslinking network (i.e., through bonding between surface groups of the CDs surrounding polymer shell) and suppressing the nonradiative decay of excited triplet state 40 . At the same time, the number of functional groups and side chains will produce different cross‐linking structures.…”

Meter-scale chemiluminescent carbon nanodot films for temperature imaging

“…As one new class of luminescent nanomaterials, carbon nanodots (CDs) composed of a sp 2 carbon skeleton and rich surface functional groups can be employed as electron donors or acceptors in various CL systems. [13][14][15][16][17][18] Compared with other counterparts, CDs exhibit excellent photostability, tunable emission wavelength, chemical stability and good biocompatibility, enabling their widespread application in light illumination, sensors and bioimaging. [19][20][21][22][23] Recently, Shen et al have achieved the efficient CL emission of CDs in peroxalate-H 2 O 2 and further developed the CL emission for information encryption, glucose detection and in vivo bioimaging, confirming the advantages of CDs as chemiluminescent nanomaterials.…”