Colorful Triplet Excitons in Carbon Nanodots for Time Delay Lighting

Abstract

Time delay lighting offers an added period of buffer illumination for human eyes upon switching off the light. Long‐lifetime emission from triplet excitons has outstanding potential, but the forbidden transition property due to the Pauli exclusion principle makes them dark, and it stays challenging to develop full‐color and bright triplet excitons. Herein, triplet excitons emission from ultraviolet (UV) to near infrared (NIR) in carbon nanodots (CNDs) is achieved by confining multicolor CNDs emitters in NaCNO crystal. NaCNO crystal can isolate the CNDs, triplet excitons quenching caused by the excited state electrons aggregation induced energy transfer is suppressed, and the confinement crystal can furthermore promote phosphorescence of the CNDs by inhibiting the dissipation of the triplet excitons due to non‐radiative transition. The phosphorescence from radiative recombination of triplet excitons in the CNDs covers the spectral region from 300 nm (UV) to 800 nm (NIR), the corresponding lifetimes can reach 15.8, 818.0, 239.7, 168.4, 426.4, and 127.6 ms. Furthermore, the eco‐friendly luminescent lampshades are designed based on the multicolor phosphorescent CNDs, time delay light‐emitting diodes are thus demonstrated. The findings will motivate new opportunities for the development of UV to NIR phosphorescent CNDs and time delay lighting applications.

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications

“…Recently, afterglow emissions from UV to NIR have been achieved by confining multicolor CDs luminophores in NaCNO crystals (CDs@NaCNO). 241 NaCNO crystals can isolate CDs, suppress T 1 exciton quenching, and provide a rigid environment to restrain NRTs to further promote phosphorescence. The phosphorescence emission maxima in CDs@NaCNO composites range from 355 nm to 685 nm (Fig.…”

The afterglow of carbon dots shining in inorganic matrices

“…42,43 The processes mentioned above are generally influenced by the molecular vibration/rotation and surrounding dissolved oxygen. 38,44 Hence, the promotion of ISC/RISC processes and inhibition of nonradiative transitions are vital for the production of afterglow effectively. 45 To date, several strategies for afterglow enhancement have been proposed, such as reinforcing spin-orbit coupling (SOC) by introducing hetero atoms, 46 heavy halogens, 47 or transition metals, 48 which are profitable for the more effective production of triplet excitons.…”

“…Additionally, nonradiative transitions can be inhibited by crystalline inducement, 39 crosslink-enhanced, 49,50 or matrix-assisted processes. 38 The matrix-assisted method principally embedded the CDs in the various rigid matrices, such as inorganic salts, 39 boric acid (BA), 51,52 silica (SiO 2 ), 53,54 urea/biuret, 55 zeolites, 37,56 NaCNO, 44,57,58 polyacrylamide (PAM), 59 cyanuric acid, 60 melamine, 61 polyvinyl alcohol (PVA), etc. [62][63][64] From many previous studies, it is clear that nano-sized CDs can be easily embedded into matrix materials and then the abundant functional groups on the surface of CDs can form strong interactions such as covalent bonds, hydrogen bonds, and ionic bonds with the matrix to construct a stable structure and achieve afterglow effectively.…”

“…70 Qiu et al prepared CDs@IMs with full-color ultralong afterglow, in which the RTP emission ranges from blue to red. 71 Due to the excellent phosphorescent properties of CDs@IMs, they have important scientific significance and application prospects in bioimaging, 53,72 fingerprint recognition, 52,73 information encryption, 71,73,74 time delay lighting, 44 and many other fields.…”

General Synthesis of Carbon Dot-Based Composites with Triple-Mode Luminescence Properties and High Stability

“…As far as optical anti-counterfeiting technology is concerned, long-lived luminescence can eliminate the interference of background fluorescence and light scattering, and greatly improve the signal-to-noise ratio of anti-counterfeiting patterns and the concealment of encrypted information. Therefore, room-temperature phosphorescence (RTP) materials are more favored for security protection including anti-counterfeiting and information encryption, compared to traditional fluorescence materials. − In recent years, carbon dot (CD)-based RTP materials have attracted more and more attention due to their significant advantages such as excellent afterglow properties, facile preparation, good stability, and low toxicity. − The matrix-assisted method has been extensively studied as the commonly used method to activate the RTP of CDs. − The CDs confined in a matrix, exhibiting a magical afterglow different from their fluorescence, are often used in anti-counterfeiting and information encryption applications. However, the dual-mode luminescence including fluorescence and phosphorescence anti-counterfeiting has been unable to meet the growing demand for high-performance optical anti-counterfeiting.…”