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

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence

Delayed luminescence (DF), including phosphorescence and thermally activated delayed fluorescence (TADF), and circularly polarized luminescence (CPL) exhibit common and broad application prospects in optoelectronic displays, biological imaging, and encryption. Thus, the combination of delayed luminescence and circularly polarized luminescence is attracting increasing attention. The encapsulation of guest emitters in various host matrices to form host-guest systems has been demonstrated to be an appealing strategy to further enhance and/or modulate their delayed luminescence and circularly polarized luminescence. Compared with conventional liquid crystals, polymers, and supramolecular matrices, porous crystalline frameworks (PCFs) including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), zeolites and hydrogen-bonded organic frameworks (HOFs) can not only overcome shortcomings such as flexibility and disorder but also achieve the ordered encapsulation of guests and long-term stability of chiral structures, providing new promising host platforms for the development of DF and CPL. In this review, we provide a comprehensive and critical summary of the recent progress in host-guest photochemistry via the encapsulation engineering of guest emitters in PCFs, particularly focusing on delayed luminescence and circularly polarized luminescence. Initially, the general principle of phosphorescence, TADF and CPL, the combination of DF and CPL, and energy transfer processes between host and guests are introduced. Subsequently, we comprehensively discuss the critical factors affecting the encapsulation engineering of guest emitters in PCFs, such as pore structures, the confinement effect, charge and energy transfer between the host and guest, conformational dynamics, and aggregation model of guest emitters. Thereafter, we summarize the effective methods for the preparation of host-guest systems, especially single-crystal-to-single-crystal (SC-SC) transformation and epitaxial growth, which are distinct from conventional methods based on amorphous materials. Then, the recent advancements in host-guest systems based on PCFs for delayed luminescence and circularly polarized luminescence are highlighted. Finally, we present our personal insights into the challenges and future opportunities in this promising field.

Recent advances in fluorescence and afterglow of CDs in matrices

Carbon dots (CDs) are novel nanomaterials with dimensions less than 10 nm that have attracted much attention due to their outstanding optical properties. However, the development of solid-state fluorescence and afterglow methods has been relatively slow, although the properties of these materials under liquid conditions have been extensively studied. In recent years, embedding CDs in a matrix has been shown to prevent aggregation quenching and inhibit nonradiative transitions, thus realizing solid-state fluorescence and afterglow, which has greatly broadened the research and application areas of CDs. In terms of hydrogen bonding, ionic bonding, covalent bonding and spatial confinement, the interactions between CDs and matrices can effectively realize and improve the solid-state fluorescence and afterglow effects of CDs. Recent applications of CDs in matrices in optoelectronics, information security, sensing, biotherapeutics and imaging are also summarized. Finally, we summarize the challenges and developments of CDs in matrices.

Time-Dependent and Excitation-Dependent Afterglow Color Evolution from the Assembly of Dual Carbon Dots in Zeolite

Afterglow materials with time-dependent color output emerge as huge prospects in advanced optical information encryption but remain a formidable challenge due to the limited exciton transfer from a single emission center. Here, multiple time-dependent afterglow color evolutions are achieved by the strategy of controllable assembly of dual carbon dots (CDs) with an individual afterglow color and decay rate into an RHO zeolite. The strategy possesses high controllability such that B-CDs and G-CDs can be independently generated and in situ embedded into a matrix; in particular, the doped amount of two kinds of CDs can be adjusted conveniently to produce interesting variable afterglow colors. Triggered by different excitations, the prepared B&G-CDs@RHO composites exhibit the conversion of TADF and RTP behaviors, as well as time-dependent afterglow color output from deep-blue to green (365 nm excitation) and static cyan (254 nm excitation). The unique luminescence and excellent stability allow the composite applied in information encryption with high-security levels.

Construction of Carbon Dots@LiCl-polyacrylamide with Humidity-Induced Ultralong Room-Temperature Phosphorescence to Fluorescence and Rigid-to-Flexible Transition Behavior

The continuous advancement of luminescent materials has placed increasingly stringent requirements on dynamic color-tunable ultralong room-temperature phosphorescence (URTP) materials that can respond to external stimuli. Nevertheless, endowing URTP materials with stimuli-response-induced dynamic color tuning is a challenging task. This study introduces a carbon dots (CDs)@LiCl-polyacrylamide (PAM) polymer system that switches from URTP to fluorescence under humidity stimuli, accompanied by a transition from rigidity to flexibility. The obtained rigid CDs@LiCl-PAM exhibits ultralong green phosphorescence with a lifetime of 560 ms in the initial state. After absorbing moisture, it becomes flexible and its phosphorescence switches off. Moreover, the emission of the CDs@LiCl-PAM film depends on the excitation wavelength. This property can potentially used in multicolored luminescence applications and displays. Moreover, multicolor luminescent patterns can be constructed in situ using the water-absorption ability of the obtained thin film and the Förster resonance energy-transfer strategy. The proposed strategy is expected to promote the interdisciplinary development of intelligent information encryption, anti-counterfeiting, and smart flexible display materials.

The afterglow of carbon dots shining in inorganic matrices

Carbon dots (CDs) are a new type of quasi-spherical and zero-dimension carbon nanomaterial with a diameter less than 10 nm. They exhibit a broad absorption spanning from the ultraviolet (UV) to visible light regions and inspire growing interests due to their excellent performance. In recent years, it was identified that the CDs embedded in various inorganic matrices (IMs) can effectively activate afterglow emission by suppressing the nonradiative transitions of molecules and protecting the triplet excitons of CDs, which hold broad application prospects. Herein, recent advances in CDs@IMs are reviewed in detail, and the interaction and luminescence mechanisms between CDs and IMs are also summarized. We highlight the synthetic strategies of constructing composites and the roles of IMs in facilitating the applications of CDs in diverse areas. Finally, some directions and challenges of future research in this field are proposed.

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

Afterglow materials are attracting widespread attention owing to their distinctive and long-lived optical emission properties which create exciting opportunities in various fields. Recent research has led to the discovery of many new afterglow materials featuring high photoluminescence quantum yields (PLQY) and lifetimes of up to several hours under ambient conditions. Afterglow materials are typically categorized according to their luminescence mechanism, such as long-persistent luminescence (LPL), room temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). Through rational design and novel synthetic strategies to modulate spin-orbit coupling (SOC) and populate triplet exciton states (T1), luminophores with long lifetimes and bright afterglow characteristics can be realized. Initial research towards afterglow materials focused mainly on pure inorganic materials, many of which possessed inherent disadvantages such as metal toxicity or low energy emissions. In recent years, organic-inorganic hybrid afterglow materials (OIHAMs) have been developed with high PLQY and long lifetimes. These hybrid materials exploit the tunable structure and easy processing of organic molecules, as well as enhanced SOC and intersystem crossing (ISC) processes involving heavy atom dopants, to achieve excellent afterglow performance. In this review, we begin by briefly discussing the structure and composition of inorganic and organic-inorganic hybrid afterglow materials, including strategies for regulating their lifetime, PLQY and luminescence wavelength. The specific advantages of organic-inorganic hybrid afterglow materials, including low manufacturing costs, diverse molecular/electronic structures, tunable structures and optical properties, and compatibility with a variety of substrates, are emphasized. Subsequently, we discuss in detail the fundamental mechanisms used by afterglow materials, their classification, design principles, and end applications (including sensing, anticounterfeiting, and photoelectric devices, among others). Finally, existing challenges and promising future directions are discussed, laying a platform for the design of afterglow materials for specific applications.

All-inorganic lead halide perovskite nanocrystals applied in advanced display devices

Advanced display devices are in greater demand due to their large color gamut, high color purity, ultrahigh visual resolution, and small size pixels. All-inorganic lead halide perovskite (AILHP) nanocrystals (NCs) possess inherent advantages such as narrow emission width, saturated color, and flexible integration, and have been developed as functional films, light sources, backlight components, and display panels. However, some drawbacks still restrict the practical application of advanced display devices based on AILHP NCs, including working stability, large-scale synthesis, and cost. In this review, we focus on AILHP NCs, review the recent progress in materials synthesis, stability improvement, patterning techniques, and device application. We also highlight the important role of materials systems in creating advanced display devices, followed by the challenges and opportunities in industrial processes. This review provides beneficial inspiration for the future development of AILHP NCs in colorful and white backlight, as well as high resolution full-color displays.

Colorful Triplet Excitons in Carbon Nanodots for Time Delay Lighting

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 of Carbon Dots with Afterglow Emission

Carbon dots (CDs) have gradually become a new generation of nano-luminescent materials, which have received extensive attention due to excellent optical properties, wide source of raw materials, low toxicity, and good biocompatibility. In recent years, there are many reports on the luminescent phenomenon of CDs, and great progress has been achieved. However,there are rarely systematic summaries on CDs with persistent luminescence. Here, a summary of the recent progress on persistent luminescent CDs, including luminous mechanism, synthetic strategies, property regulation, and potential applications, is given. First, a brief introduction is given to the development of CDs luminescent materials. Then, the luminous mechanism of afterglow CDs from room temperature phosphorescence (RTP), delayed fluorescence (DF), and long persistent luminescence (LPL) is discussed. Next, the constructed methods of luminescent CDs materials are summarized from two aspects, including matrix-free self-protected and matrix-protected CDs. Moreover, the regulation of afterglow properties from color, lifetime, and efficiency is presented. Afterwards, the potential applications of CDs, such as anti-counterfeiting, information encryption, sensing, bio-imaging, multicolor display, LED devices, etc., are reviewed. Finally, an outlook on the development of CDs materials and applications is proposed.