Brighten Triplet Excitons of Carbon Nanodots for Multicolor Phosphorescence Films

Abstract

Triplet excitons usually do not emit light under ambient conditions due to the spin-forbidden transition rule, thus they are called dark excitons. Herein, triplet excitons in carbon nanodots (CNDs) are brightened by embedding the CNDs into poly(vinyl alcohol) (PVA) films; flexible multicolor phosphorescence films are thus demonstrated. PVA chains can isolate the CNDs, and excited state electron or energy transfer induced triplet exciton quenching is thus reduced; while the formed hydrogen bonds between the CNDs and PVA can restrict vibration/rotation of the CNDs, thus further protecting the triplet excitons from nonradiative recombination. The lifetimes of the flexible multicolor phosphorescence films can reach 567, 1387, 726, and 311 ms, and the longest-lasting phosphorescence film can be observed by naked eyes for nearly 15 s even after bending 5000 times. The phosphorescence films can be processed into various patterns, and a dynamic optical signature concept has been proposed and demonstrated based on the phosphorescence films.

A Molecular Engineering Strategy for Achieving Blue Phosphorescent Carbon Dots with Outstanding Efficiency above 50%

“…Note that no afterglow emission could be detected at room temperature through embedding seed‐CDs into matrices (e.g., polyvinyl alcohol (PVA), Figure S13, Supporting information) that commonly being used to modify CDs, indicating that only hydrogen bonding fixation is not sufficient to activate RTP of seed‐CDs. [ 24,48 ] Besides that, as shown in Figure S14, Supporting Information), it can be found that the urea molecule has no direct effect on the surface states of CDs because no phosphorescence was observed from the physical blends of the seed‐CDs and urea. There is also no phosphorescence can be observed from B‐CDs 80 300 , and the XRD pattern of B‐CDs 80 300 is also almost the same as u‐seed‐CDs (Figures S15 and S16, Supporting Information).…”

“…And the SiO 2 in the matrix could effectively form hydrogen bonds with these groups, being expected to reduce their vibration‐induced non‐radiative transition, which can be verified by the blueshift of OH related vibration peak from 3370 to 3429 cm −1 and more thermogravimetric loss for the B‐CDs 300 sample when compared with the seed‐CDs (Figure S9, Supporting information). [ 48 ] In addition, it is also intriguing to observe that the stretching vibration intensity of CO at 1609 cm −1 increases obviously from seed‐CDs to B‐CDs 300 sample, and an additional vibration peaked at 1662 cm −1 assigned to the stretching vibration of CN in CNH groups can be also observed in B‐CDs 300 , indicating that more CO and CN bands have been formed on the surface of B‐CDs 300 . [ 40,49 ]…”

Time‐Dependent Polychrome Stereoscopic Luminescence Triggered by Resonance Energy Transfer between Carbon Dots‐in‐Zeolite Composites and Fluorescence Quantum Dots

“…Therefore, in this work, integrating CDs@zeolite composites and PeQDs into a container to shorten the radiation distance between energy donors and energy acceptors is a facile approach to achieving efficient RET. According to a reported equation, [ 42 ] based on the afterglow lifetimes of CDs@zeolite‐2 and Orange/Red‐PeQDs, the PLQY of Orange/Red‐PeQDs (Table S1, Supporting Information), as well as the afterglow QY of CDs@zeolite‐2 (6.2%), the afterglow QY of Orange/Red‐PeQDs are calculated to be 4.3% and 5.5%, respectively. Detailed computing methods and discussions are shown in Supporting Information.…”

One-Pot Three Carbon Dots with Various Lifetimes Rooted in Different Decarboxylation Degrees for Matrix-Free, Anti-Oxygen, and Time-Resolved Information Encryption and Cellular Imaging

“…These groups featuring n –π* transition absorption and emission characteristics are formed by the reaction between/among precursors, carbonization at high temperatures, and/or oxidation by water or oxidants. When they anchored on the surface of the C-dots, various matrices were required to immobilize the external n –π* emissive center for activating RTP. − Reversely, if these groups were embedded in the interior of C-dots, the internal hydrogen bonds and polymer-like covalent bonds of C-dots as self-matrices can “lock” the internal triplet excitons, efficiently suppressing the nonradiative relaxation. − Therefore, long-lived afterglows in the exterior and interior of the C-dots were observed. Two types of matrix-free RTPs of the C-dots were fabricated due to the low energy gap between S 1 and T 1 (Δ E ST ) , and heavy atom effect. − Unfortunately, many C-dots-based RTPs can be observed in the solid state because these C-dots are highly hydrophilic and easily infiltrated by water containing dissolved oxygen, resulting in the insufficiency of RTP in aqueous solution .…”