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Water-soluble red afterglow imaging agents based on ecofriendly nanomaterials have potential application in time-gated afterglow bioimaging due to their larger penetration depth and nondurable excitation. Herein, red afterglow imaging agents consisted of Rhodamine B (RhB) and carbon nanodots (CNDs) have been designed and demonstrated. In these agents, CNDs act as energy donors, and RhB acts as an energy acceptor. Both of them are confined into a hydrophilic silica shell to form a CNDs-RhB@silica nanocomposite. The phosphorescence emission spectrum of the CNDs and the absorption spectrum of the RhB match well, and efficient energy transfer from the CNDs to the RhB via Förster resonant energy transfer process can be achieved, with a transfer efficiency can reach 99.2%. Thus, the as-prepared nanocomposite can emit a red afterglow in aqueous solution, and the afterglow spectrum of CNDs-RhB@silica nanocomposite can extend to the first near-infrared window (NIR-I). The luminescence lifetime and afterglow quantum yield (QY) of the CNDs-RhB@silica can reach 0.91 s and 3.56%, respectively, which are the best results in red afterglow region. Time-gated in vivoafterglow imaging has been demonstrated by using the CNDs-RhB@silica as afterglow agents.

Optical multiplexing technology plays a crucial role in various fields such as data storage, anti-counterfeiting, and time-resolved biological imaging. Nevertheless, employing single-wavelength phosphorescence for multiplexing often results in spectral overlap among the emission peaks of various channels, which can precipitate crosstalk and misinterpretation in the information-decoding process, thereby compromising the integrity and precision of the encrypted data. This paper proposes a time-divided colorful multiplexing technology based on phosphorescent carbon nanodots with different colors and lifetimes. Using different luminescence colors to symbolize varying information levels helps achieve multitiered information encryption and storage. By modulation of the lifetime and the emission wavelength, intricate information can be encoded, thereby enhancing the intricacy and security of the encryption mechanism. By assigning different data bits to each color, more information can be encoded in the same physical space. This method enables higher-density information storage and fortifies encryption, ensuring the compactness and security of information.

A scene that contains both old and instant events with a clear motion trail is visually intriguing and dynamic, which can convey a sense of change, transition, or evolution. Developing an eco-friendly delay display system offers a powerful tool for fusing old and instant events, which can be used for visualizing motion trails. Herein, we brighten triplet excitons of carbon nanodots (CNDs) and increase their emission yield by a multidimensional confinement strategy, and the CND-based delay display array is demonstrated. The intense confinement effects via multidimensional confinement strategy suppress nonradiative transitions, and 240% enhancement in the phosphorescence efficiency and 260% enhancement in the lifetime of the CNDs are thus realized. Considering their distinctive phosphorescence performances, a delay display array containing a 4 × 4 CND-based delay lighting device is demonstrated, which can provide ultralong phosphorescence over 7 s, and the motion that occurred in different timelines is recorded clearly. This finding will motivate the investigation of phosphorescent CNDs in motion trail recognition.

Nanocarbon as an eco-friendly and abundant material has strong multi-color fluorescence, which makes it a promising candidate for healthy lighting and display. However, the low fluorescence efficiency and poor stability of multi-color carbon nanoparticle (CNP) phosphors are main hurdles that hinder their applications. This work demonstrated efficient and stable multi-color CNP phosphors through synergy between inner polar groups and outer silica matrix. The polar groups in polyethylene glycol (PEG) 6,000 are favor of high fluorescence of the CNP phosphors, and the low melting point (64°C) of PEG 6,000 helps to improve the thermal stability of the phosphors, while the silica matrix provides protection to the phosphors. Based on this design, blue, green, yellow and red CNP phosphors with photoluminescence quantum yield of 53.1%, 47.4%, 43.8% and 42.3% have been achieved, all of which are the best values in ever reported multi-color CNP phosphors. Furthermore, the fluorescence of the CNP phosphors keeps almost unchanged at 100°C and degrades little in one month, indicating their good thermal tolerance and temporal stability. In addition, multicolor devices including white light-emitting devices (LEDs) have been realized by coating the CNP phosphors onto UV chips. The luminous efficiency, correlated color temperature, Commission Internationale de L’Eclairage and color rendering index of the white LED can reach 12 lm W−1, 6,107 K, (0.32, 0.33) and 89, respectively, indicating the potential applications of the CNP phosphors in lighting and display. 纳米碳作为一种资源丰富的环境友好型材料, 会产生明亮的多色荧光, 成为一种在健康照明与显示领域有前景的材料. 然而多色碳 纳米粒子荧光粉的荧光效率和稳定性仍然低于预期, 这极大地限制了碳纳米粒子的应用. 本工作通过内层极性官能团与外层二氧化硅的 协同作用, 制备了高效稳定的多色碳纳米颗粒荧光粉. 聚乙二醇6000中的官能团有利于碳纳米粒子的发光, 其较低的熔点(64°C)提升了碳 纳米粒子的热稳定性, 而外层的二氧化硅对荧光粉提供了保护作用. 基于这个设计, 制备出了量子效率为53.1%, 47.4%, 43.8%以及42.3%的 蓝光、绿光、黄光和红光碳纳米粒子荧光粉, 量子效率均为已报道的多色碳纳米粒子荧光粉的最高值. 所制备的碳纳米粒子荧光粉展现 了良好的热稳定性和时间稳定性, 其荧光在100°C和一个月后仍能保持不变. 将所制备的碳纳米粒子荧光粉涂覆到紫外芯片上, 实现了包 括白光在内的多色发光器件. 其中, 白光器件的流明效率为12 lm W−1, 色温, 色坐标和显色指数分别为6107 K, (0.32,0.33)和89, 表明碳纳米 粒子荧光粉在照明与显示领域有潜在的应用前景.

The easy-to-imitate character of a personal signature may cause significant economy loss due to the lack of speed and strength information. In this work, we report a time-resolved anti-counterfeiting signature strategy with artificial intelligence (AI) authentication based on the designed luminescent carbon nanodot (CND) ink, whose triplet excitons can be activated by the bonding between the paper fibers and the CNDs. Paper fibers can bond with the CNDs through multiple hydrogen bonds, and the activated triplet excitons release photons for about 13 s; thus, the speed and strength of the signature are recorded through recording the changes in luminescence intensity over time. The background noise from commercial paper fluorescence is completely suppressed, benefiting from the long phosphorescence lifetime of the CNDs. In addition, a reliable AI authentication method with quick response based on a convolutional neural network is developed, and 100% identification accuracy of the signature based on the CND ink is achieved, which is higher than that of the signature with commercial ink (78%). This strategy can also be expanded for painting, calligraphy identification.

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.