Multilevel Data Encryption Using Thermal-Treatment Controlled Room Temperature Phosphorescence of Carbon Dot/Polyvinylalcohol Composites

Ultrasensitive detection of tetracycline using the disruption of crosslink-enhanced emission and inner-filter effect-induced phosphorescence quenching of carbonized polymer dots

Accumulation of tetracycline (TC) in the environment and food may lead to potential health risks and the emergence of antibiotic-resistant bacteria. To meet the demand for sensitivity, ease of use, and portability in detecting TCs, we fabricated a green phosphorescent film consisting of crosslinked polymer-integrated carbon dots (named carbonized polymer dots, CPD) and polyvinyl alcohol (PVA) polymers for ultrasensitive sensing of TCs via the inner filter effect-mediated phosphorescence quenching and the disruption of the crosslink-enhanced emission (CEE) effect by TC. To create polymer structures on the carbon dots for interaction with PVA, CPDs were synthesized via low-temperature hydrothermal treatment using citric acid and cysteine. Compared to products with oxidized sulfur or no sulfur doping, the incorporation of nitrogen and sulfur in CPDs was found to effectively facilitate intersystem crossing, significantly enhancing phosphorescence. By measuring the phosphorescence properties of compounds inside and outside the dialysis bag at different dialysis times, we confirmed that crosslinking interactions between CPD and PVA polymers can create a rigid environment to amplify the phosphorescence of sub-luminophores (e.g., hydroxyl, carboxyl, and amino groups) through the CEE effect. These features make the CPD/PVA film an effective tool for phosphorescence turn-off detection of TC, offering a wide linear detection range (1 nM-1 mM), a low limit of detection (0.7 nM), and good selectivity over potential interfering substances, such as metal ions, amino acids, fatty acids, and lactose. Our finding indicates that the TC-triggered phosphorescence quenching of the CPD/PVA film originates from TC-mediated IFE effect and TC-disrupted CEE effect. The CPD/PVA film was shown to establish a linear calibration curve to quantify TC in drinking water and milk samples with good recoveries (84 %-120 %).

Intricacies of Carbon Dot Photoluminescence for Emerging Applications: A Review

Discovered only in 2004, carbon dots (CDs) have already traversed a long journey, generating many promising research directions. Its cheapness, ease of synthesis, high water-solubility, tunable emission, and excellent biocompatibility make it a single-point solution to many problems, and tremendous efforts were invested into understanding the structure-property-function relationship, which eases the engineering of the CD properties suitable for a desired application. From the usual random choice of precursors or carbon materials as a starting point in the early days, more systematic approaches are now available for choosing proper starting materials and appropriate experimental conditions (solvent medium, reaction temperature, reaction duration, pH, etc) to customize its photoluminescence. The presence of impurities has a crucial role in the outcome and applicability of photoluminescence. Recently, a significant focus has been on the long-wavelength emissive CDs, particularly in the red to near-infrared (NIR) regions, for better penetration into live cells and to circumvent autofluorescence problems. Proper design can harvest phosphorescence from CDs. Many excellent reviews are available, focusing on different facets of CD prospects. Hence, we will only highlight the importance of the optical properties of CDs and ways to modulate them. We will mention some of the new works that have appeared in the last five years.

The Accurate Synthesis of a Multiscale Metallic Interface on Graphdiyne

The accurate construction of composite material systems containing graphdiyne (GDY) and other metallic materials has promoted the formation of innovative structures and practical applications in the fields of energy, catalysis, optoelectronics, and biomedicine. To fulfill the practical requirements, the precise formation of multiscale interfaces over a wide range, from single atoms to nanostructures, plays an important role in the optimization of the structural design and properties. The intrinsic correlations between the structure, synthesis process, characteristic properties, and device performance are systematically investigated. This review outlines the current research achievements regarding the controlled formation of multiscale metallic interfaces on GDY. Synthetic strategies for interface regulation, as well as the correlation between the structure and performance, are presented. Furthermore, innovative research ideas for the design and synthesis of functional metal-based materials loaded onto GDY-based substances are also provided, demonstrating the promising application potential of GDY-based materials.

Luminescence Properties of Hoechst 33258 in Polyvinyl Alcohol Films

We report a comprehensive investigation of the photophysical properties of Hoechst 33258 (HOE) embedded in polyvinyl alcohol (PVA) films. HOE displays a bright, highly polarized, blue fluorescence emission centered at 430 nm, indicating effective immobilization within the polymer matrix of PVA. Its fluorescence quantum yield is notably high (~0.74), as determined relative to a quinine sulfate standard. In addition, we observed that HOE-doped PVA films exhibit room temperature phosphorescence (RTP) that remains visible for several seconds after UV excitation ceases. The slightly negative phosphorescence anisotropy implies that the triplet-singlet radiative transition is orthogonal to the singlet-singlet transition governing fluorescence. Notably, we observed that direct triplet-state excitation at longer wavelengths (beyond the primary absorption band) produces highly polarized RTP. We believe this possibility of direct triplet-state excitation opens new avenues for studying RTP in polymer-immobilized molecules.

CO2-Sourced Polymer Dyes for Dual Information Encryption

Large amounts of small molecule dyes leak into the ecosystems annually in harmful and unsustainable ways. Polymer dyes have attracted much attention because of their high migration resistance, excellent stability, and minimized leakage. However, the complex synthesis process, high cost, and poor degradability hinder their widespread application. Herein, green and sustainable polymer dyes are prepared using natural dye quercetin (Qc) and CO2 through a one-step process. The CO2-sourced polymer dyes show strong migration resistance, high stability, and can be degraded on demand. Additionally, the CO2-sourced polymer dyes showed unique responses to Zn2+, leading to significantly enhanced fluorescence, highlighting their potential for information encryption/decryption. The CO2-sourced polymer dyes can solve the environmental hazards caused by small molecule dye leakage and promote the carbon cycle process. Meanwhile, the one-step synthesis process is expected to achieve sustainable and widespread utilization of CO2-sourced polymer dyes.

High-yield upcycling of feather wastes into solid-state ultra-long phosphorescence carbon dots for advanced anticounterfeiting and information encryption

Recently, biomass-derived carbon dots (CDs) have attracted considerable attention in high-technology fields due to their prominent merits, including brilliant luminescence, superior biocompatibility, and low toxicity. However, most of the biomass-derived CDs only show bright fluorescence in diluted solution because of aggregation-induced quenching effect, hence cannot exhibit solid-state long-lived room-temperature phosphorescence (RTP) in ambient conditions. Herein, matrix-free solid-state RTP with an average lifetime of 0.50 s is realized in the CDs synthesized by one-pot hydrothermal treatment of duck feather waste powder. To further enhance RTP lifetime, hydrogen bonding is introduced by employing polyols like polyvinyl alcohol (PVA) and phytic acid (PA), and a bimodal luminescent CDs/PVA/PA ink is exploited by mixing the CDs and polyols. Astonishingly, the CDs/PVA/PA ink screen-printed onto cellulosic substrates exhibits unprecedented green RTP with average lifetime of up to 1.97 s, and the afterglow lasts for more than 14 s after removing UV lamp. Such improvement on RTP is proposed to the populated excited triplet excitons stabilized by rigid chains. Furthermore, the CDs/PVA/PA ink demonstrates excellent potential in anticounterfeiting and information encryption. To the best of the authors' knowledge, this work is the first successful attempt to fabricate matrix-free ultra-long RTP CDs by reclamation of the feather wastes for environmental sustainability.

Vacuum-Boosting Precise Synthetic Control of Highly Bright Solid-State Carbon Quantum Dots Enables Efficient Light Emitting Diodes

Carbon quantum dots (C-dots) have emerged as efficient fluorescent materials for solid-state lighting devices. However, it is still a challenge to obtain highly bright solid-state C-dots because of the aggregation caused quenching. Compared to the encapsulation of as-prepared C-dots in matrices, one-step preparation of C-dots/matrix complex is a good method to obtain highly bright solid-state C-dots, which is still quite limited. Here, an efficient and controllable vacuum-boosting gradient heating approach is demonstrated for in situ synthesis of a stable and efficient C-dots/matrix complex. The addition of boric acid strongly bonded with urea, promoting the selectivity of the reaction between citric acid and urea. Benefiting from the high reaction selectivity and spatial-confinement growth of C-dots in porous matrices, in situ synthesize C-dots bonded can synthesized dominantly with a crosslinked octa-cyclic compound, biuret and cyanuric acid (triuret). The obtained C-dots/matrix complex exhibited bright green emission with a quantum yield as high as 90% and excellent thermal and photo stability. As a proof-of-concept, the as-prepared C-dots are used for the fabrication of white light-emitting diodes (LEDs) with a color rendering index of 84 and luminous efficiency of 88.14 lm W-1, showing great potential for applications in LEDs.

Supramolecular Assembly of Hydrogen-Bonded Organic Frameworks with Carbon Dots: Realizing Ultralong Aqueous Room-Temperature Phosphorescence for Anticounterfeiting

Room-temperature phosphorescent carbon dots (RTP-CDs) have received increasing attention due to their excellent optical properties and potential applications. Nevertheless, the realization of RTP-CDs in aqueous solutions remains a considerable challenge due to the water-molecule- and oxygen-induced deactivation of the triplet excitons, which leads to phosphorescence quenching. In this study, ultralong phosphorescence in water was achieved by in situ self-assembly of CDs encapsulated in a rigid hydrogen-bonded organic framework (HOF). The phosphorescence lifetime reaches an impressive 956.96 ms and exhibits long-lasting optical and structural stability in water for more than 90 days. The composite material not only has ultralong luminescence life and excellent luminescence stability but also has two-color phosphorescence emission, as well as excellent antiphotobleaching and phosphorescence stability in aqueous solution, which can solve the current problem that RTP is easily burst out by water and moisture. In addition, this study introduced a fluorescent dye based on the triplet-singlet Förster resonance energy transfer system (TS-FRET) to fine-tune the afterglow properties. This work will inspire the design of RTP systems with dual phosphor light sources and provide new strategies for the development of smart RTP materials in water.

Thermal Annealing Effects on Long-Lived Fluorenol Room Temperature Phosphorescence for Styrene Detection

Fluorene derivatives have been widely developed in OLEDs because of its efficient fluorescence quantum efficiency, but for which unique rigid biphenyl planar structure and large conjugated system, we hypothesize that they have a great potential for room temperature phosphorescence (RTP) applications, and confirmed this conjecture by subjecting polyvinyl alcohol (PVA) and phosphors to thermal annealing. The cross-linked structure formed during thermal annealing judiciously modulates the phosphorescence emission characteristics of the fluorenol with the synergistic interaction between PVA and fluorenol. Specifically, the lifetime exhibited a substantial increase from 1352.2 ms to 2874.1 ms, accompanied by a quantum yield augmentation from 4.8 % to 11.3 %, which substantiate that cross-linked induced by thermal annealing effectively amplifies the phosphorescent intensity and stability of the phosphors, facilitating ultralong phosphorescent emission at ambient conditions. Furthermore, an effective probe based on this film is developed for its highly sensitive, quantitative and immediate detection of volatile organic compounds. This investigation not only proffers a novel paradigm for the development of advanced RTP materials but also imparts insightful considerations for optimizing the performance of polymers in conjunction with functional materials, encompassing bioimaging, sensing, and optoelectronic devices.

Utilizing weakly donor-acceptor ternary π-conjugated architecture to achieve single-component white luminescence and stimulus-responsive room-temperature phosphorescence

Purely organic room-temperature phosphorescence (RTP) has garnered substantial attention for its delayed emission, environmental sensitivity, and potential diverse applications. However, the quest for high-performance RTP materials has always been a challenge. In this study, we introduce novel weakly donor-acceptor (D-A) ternary π-conjugated architecture to construct an efficient RTP system. The strategy utilizes synergistic effects of the analogous El-Sayed rule, halogen-free heavy-atom effect, reduction of the singlet-triplet energy gap, and manipulation of flexible molecular conformation. A remarkable enhancement in the phosphorescence-to-fluorescence ratio was achieved, elevating from 0.4 in carbazole to 35.2 in DBTDBTCZ. Furthermore, the RTP system demonstrates single-component white luminescence, yielding warm and cool white colors. Intriguingly, we unveil the novel position-dependent heavy-atom effects, discerningly promoting intersystem crossing or phosphorescence decay. Benefiting from efficient RTP, multifunctional applications of real-time humidity monitoring, oxygen sensing, anti-counterfeiting labeling, and white lighting are demonstrated.

Photo-controlled order-to-order host-guest self-assembly transfer for an afterglow effect with water resistance

Due to the general incompleteness of photochemical reactions, the photostationary structure in traditional photo-controlled host-guest self-assembly transfer is usually disordered or irregular. This fact readily affects the photoregulation or improvement of related material properties. Herein, a photoexcitation-induced aggregation molecule, hydroxyl hexa(thioaryl)benzene (HB), was grafted into β-cyclodextrin to form a host-guest system. Upon irradiation, the excited state conformational change of HB can drive an order-to-order phase transition of the system, enabling the transfer of the initial linear nanostructure to a photostationary worm-like nanostructure with orderliness and crystallinity capability. Along with the photoexcitation-controlled phase transition, an afterglow effect was obtained from the films prepared by doping the host-guest system into poly(vinyl alcohol). The afterglow effect had a superior water resistance, which successfully overcame the general sensitivity of doped materials with the afterglow effect to water vapor. These results are expected to provide new insights for pushing forward chemical self-assembly from the light perspective, towards materials with superior and stable properties under light treatment.

The Emerging Star of Carbon Luminescent Materials: Exploring the Mysteries of the Nanolight of Carbon Dots for Optoelectronic Applications

Carbon dots (CDs), a class of carbon-based nanomaterials with dimensions less than 10 nm, have attracted significant interest since their discovery. They possess numerous excellent properties, such as tunability of photoluminescence, environmental friendliness, low cost, and multifunctional applications. Recently, a large number of reviews have emerged that provide overviews of their synthesis, properties, applications, and their composite functionalization. The application of CDs in the field of optoelectronics has also seen unprecedented development due to their excellent optical properties, but reviews of them in this field are relatively rare. With the idea of deepening and broadening the understanding of the applications of CDs in the field of optoelectronics, this review for the first time provides a detailed summary of their applications in the field of luminescent solar concentrators (LSCs), light-emitting diodes (LEDs), solar cells, and photodetectors. In addition, the definition, categories, and synthesis methods of CDs are briefly introduced. It is hoped that this review can bring scholars more and deeper understanding in the field of optoelectronic applications of CDs to further promote the practical applications of CDs.

Comprehensive Overview of Controlled Fabrication of Multifunctional Fluorescent Carbon Quantum Dots and Exploring Applications

In recent years, carbon dots (CDs) have garnered increasing attention due to their simple preparation methods, versatile performances, and wide-ranging applications. CDs can manifest various optical, physical, and chemical properties including quantum yield (QY), emission wavelength (Em), solid-state fluorescence (SSF), room-temperature phosphorescence (RTP), material-specific responsivity, pH sensitivity, anti-oxidation and oxidation, and biocompatibility. These properties can be effectively regulated through precise control of the CD preparation process, rendering them suitable for diverse applications. However, the lack of consideration given to the precise control of each feature of CDs during the preparation process poses a challenge in obtaining the requisite features for various applications. This paper is to analyze existing research and present novel concepts and ideas for creating CDs with different distinct features and applications. The synthesis methods of CDs are discussed in the first section, followed by a comprehensive overview of the important properties of CDs and the modification strategy. Subsequently, the application of CDs and their requisite properties are reviewed. Finally, the paper outlines the current challenges in controlling CDs properties and their applications, discusses potential solutions, and offers suggestions for future research.

Influence of chemical treatment and interaction with matrix on room temperature phosphorescence of carbon dots

In this work, composite materials were formed based on various matrices (polymer and porous cellulose matrix) and carbon dots (CDs) with intense room-temperature phosphorescence (RTP). The effect of post-synthesis chemical treatment with citric acid or urea on the optical properties of composites was studied: the increase in carboxy and carbonyl groups led to an increase of RTP signals that could be seen with the naked eye over several seconds. The fabricated composites demonstrated good stability and reversibility of RTP signals by mild heating. Based on the developed CDs, luminescent inks were used for a simple demonstration of the data encryption on paper.

Dynamic Room Temperature Phosphorescence of Silane-Functionalized Carbon Dots Confining within Silica for Anti-Counterfeiting Applications

Room temperature phosphorescent (RTP) materials with long-lived, excitation-dependent, and time-dependent phosphorescence are highly desirable but very hard to achieve. Herein, this work reports a rational strategy of multiple wavelength excitation and time-dependent dynamic RTP color by confining silane-functionalized carbon dots (CDs) in a silica matrix (Si-CDs@SiO2). The Si-CDs@SiO2 possesses unique green-light-excitation and a change in phosphorescence color from yellow to green. A slow-decaying phosphorescence at 500 nm with a lifetime of 1.28 s and a fast-decaying phosphorescence at 580 nm with a lifetime of 0.90 s are observed under 365 nm of irradiation, which originated from multiple surface triplet states of the Si-CDs@SiO2. Given the unique dynamic RTP properties, the Si-CDs@SiO2 are demonstrated for applications in fingerprint recognition and multidimensional dynamic information encryption. These findings will open an avenue to explore dynamic phosphorescent materials and significantly broaden their applications.

Carbon Dots and Their Polymeric Nanocomposites: Insight into Their Synthesis, Photoluminescence Mechanisms, and Recent Trends in Sensing Applications

Carbon dots (CDs), a novel class of carbon-based nanoparticles, have received a lot of interest recently due to their exceptional mechanical, chemical, and fluorescent properties, as well as their excellent photostability and biocompatibility. CDs' emission properties have already found a variety of potential applications, in which bioimaging and sensing are major highlights. It is widely acknowledged that CDs' fluorescence and surface conditions are closely linked. However, due to the structural complexity of CDs, the specific underlying process of their fluorescence is uncertain and yet to be explained. Because of their low toxicity, robust and wide optical absorption, high chemical stability, rapid transfer characteristics, and ease of modification, CDs have been recognized as promising carbon nanomaterials for a variety of sensing applications. Thus, following such outstanding properties of CDs, they have been mixed and imprinted onto different polymeric components to achieve a highly efficient nanocomposite with improved functional groups and properties. Here, in this review, various approaches and techniques for the preparation of polymer/CDs nanocomposites have been elaborated along with the individual characteristics of CDs. CDs/polymer nanocomposites recently have been highly demanded for sensor applications. The insights from this review are detailed sensor applications of polymer/CDs nanocomposites especially for detection of different chemical and biological analytes such as metal ions, small organic molecules, and several contaminants.

Carbon Quantum Dots for Long-Term Protection against UV Degradation and Acidification in Paper-Based Relics

Paper-based cultural relics constitute a significant and invaluable part of human civilization and cultural heritage. However, they are highly vulnerable to environmental factors such as ultraviolet (UV) photodegradation and acidification degradation, posing substantial threats to their long-term preservation. Carbon quantum dots (CQDs), known for their outstanding optical properties, high water solubility, and good safety, offer a promising solution for slowing down UV damage and acidification of paper-based relics during storage and transportation. Herein, we propose a feasible strategy for the simple preparation of CQDs with high dispersion stability, excellent UV absorption, room-temperature phosphorescence, and photostability for the safety protection of paper. Accelerated aging experiments were conducted using UV and dry-heat aging methods on both CQD-protected paper and unprotected paper, respectively, to evaluate the effectiveness of CQD protection. The results demonstrate a slowdown in both the oxidation and acid degradation processes of the protected paper under both UV-aging and dry-heat aging conditions. Notably, CQDs with complex luminescence patterns of both fluorescence and room-temperature phosphorescence also endue them as enhanced optical anticounterfeiting materials for multifunctional paper protection. This research provides a new direction for the protection of paper-based relics with emerging carbon nanomaterials.

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.

Pyrolysis of Al-Based Metal-Organic Frameworks to Carbon Dot-Porous Al2 O3 Composites With Time-Dependent Phosphorescence Colors for Advanced Information Encryption

Phosphorescent materials with time-dependent phosphorescence colors (TDPCs) have great potential in advanced optical applications. Synthesis of such materials is attractive but challenging. Here, a series of carbon dot-porous Al2 O3 composites exhibiting distinctive TDPC characteristics is prepared by high-temperature pyrolysis of Al-based metal-organic frameworks NH2 -MIL-101(Al). The composite synthesized at 700 °C (CDs@Al2 O3 -700) shows an obvious change in phosphorescence color from blue to green after removing the excitation light of 280 nm. Photophysical analysis reveals that two emission centers in CDs, namely carbon core and surface states, are responsible for the short-lived blue phosphorescence (96 ms) and long-lived green phosphorescence (911 ms), respectively. The combination of blue and green phosphorescence with different decay rates triggering the interesting TDPC phenomenon. CDs@Al2 O3 -700 has a significantly high phosphorescence quantum yield of up to 41.7% and possesses an excellent optical stability against water, organic solvents, and strong oxidants, which benefits from the multi-confinement of CDs by the porous Al2 O3 matrix through rigid network, strong space constraint, and stable covalent bonding. Based on the TDPC property, multilevel coding patterns composed of CDs@Al2 O3 are successfully fabricated for advanced dynamic information encryption.

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.

A General Strategy for Developing Ultrasensitive "Transistor-Like" Thermochromic Fluorescent Materials for Multilevel Information Encryption

Thermochromic fluorescent materials (TFMs) exhibit great potential in information encryption applications but are limited by low thermosensitivity, poor color tunability, and a wide temperature-responsive range. Herein, a novel strategy for constructing highly sensitive TFMs with tunable emission (450-650 nm) toward multilevel information encryption is proposed, which employs polarity-sensitive fluorophores with donor-acceptor-donor (D-A-D) type structures as emitters and long-chain alkanes as thermosensitive loading matrixes. The structure-function relationships between the performance of TFMs and the structures of both fluorescent emitters and phase-change molecules are systematically studied. Benefiting from the above design, the obtained TFMs exhibit over 9500-fold fluorescence enhancement toward the temperature change, as well as ultrahigh relative temperature sensitivity up to 80% K-1 , which are first confirmed. Thanks to the superior transducing performance, the above-prepared TFMs can be further developed as information-storage platforms within a relatively narrow interval of temperature variation, including temperature-dominated multicolored information display and multilevel information encryption. This work will not only provide a novel perspective for designing superior TFMs for information encryption but also bring inspiration to the design and preparation of other response-switching-type fluorescent probes with ultrahigh conversion efficiency.

A photo-controlled fluorescent switching based on carbon dots and photochromic diarylethene for bioimaging

Carbon dots (CDs) as luminescent zero-dimensional carbon nanomaterials have good aqueous dissolution, photostability, high quantum yield, and tunability of emission color. It has great application potential in many fields, including bioimaging, labeling of biological species, drug delivery, and sensing in biomedical. However, controlling the fluorescence emission of carbon dots remains a formidable challenge. Herein, we designed and exploited a photo-controlled fluorescent switching based on photochromic diarylethene (DT) and CDs for bioimaging. It could be modulated reversibly between "ON" and "OFF" under UV/vis light exposure. The fluorescent modulation efficiency was as high as 95.3%. The fluorescent switching could be used to the bioimaging in HeLa cells with low cell toxicity. Therefore, this fluorescent switching could be a promising candidate in many potential application areas, especially in bioimaging.

Phosphorescence, fluorescence, and colorimetric triple-mode sensor for the detection of acid phosphatase and corresponding inhibitor

Acid phosphatase (ACP) as a clinical diagnostic biomarker for several pathophysiological diseases has aroused widespread interest. Compared to commonly developed single-mode ACP detection technology, the multi-mode detection method with self-validation can provide more reliable results. Herein, we proposed a triple-mode phosphorescence, fluorescence, and colorimetric method for ACP detection in combination with CDs@SiO₂. HAuCl₄ with oxidase-like activity can catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to the blue oxide TMB (TMBox), offering absorption signals and quenching the phosphorescence and fluorescence of CDs@SiO₂ based on the internal filtration effect (IFE). ACP can hydrolyze ascorbic acid 2-phosphate (AAP) to yield ascorbic acid (AA), thereby reducing TMBox to TMB, triggering solution fading and restoring phosphorescence and fluorescence signals. When the ACP inhibitor malathion is present, the reduction of TMBox is hindered, which successively led to the suppression of CDs@SiO₂ phosphorescence and fluorescence signal recovery. According to these principles, triple-mode ACP (LOD = 0.0026 mU mL^-1) and malathion detections (LOD = 0.039 μg mL^-1) with favorable accuracy and sensitivity are realized. With simplicity, robustness, and versatility, the triple-mode sensor can be extended to the detection of the AAP hydrolase family and the screening of corresponding inhibitors.

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

Carbon dot (CD)-based luminescent materials have attracted great attention in optical anti-counterfeiting due to their excellent photophysical properties in response to ultraviolet-to-visible excitation. Hence, there is an urgent need for the general synthesis of CD-based materials with multimode luminescence properties and high stability; however, their synthesis remains a formidable challenge. Herein, CDs were incorporated into a Yb,Tm-doped YF3 matrix to prepare CDs@YF3:Yb,Tm composites. The YF3 plays a dual role, not only serving as a host for fixing rare earth luminescent centers but also functioning as a rigid matrix to stabilize the triplet state of the CDs. Under the excitation of 365 nm ultraviolet light and 980 nm near-infrared light, CDs@YF3:Yb,Tm exhibited blue fluorescence and green room-temperature phosphorescence of CDs and upconversion luminescence of Tm3+, respectively. Due to the strong protection of the rigid matrix, the stability of CDs@YF3:Yb,Tm is greatly improved. This work provides a general synthesis strategy for achieving multimode luminescence and high stability of CD-based luminescent materials and offers opportunities for their applications in advanced anti-counterfeiting and information encryption.

Activating Molecular Room-Temperature Phosphorescence by Manipulating Excited-State Energy Levels in Poly(vinyl alcohol) Matrix

Poly(vinyl alcohol) (PVA) has been found as a wonderful matrix for chromophores to boost their room-temperature phosphorescence (RTP) character by forming abundant hydrogen bonding. Despite the well-utilized protective effect, the constructive role in accelerating the intersystem crossing is less investigated. Here, we focus on its role in manipulating the excited-state energy level to facilitate multiple intersystem crossing channels. Six benzoyl carbazole derivatives do not emit RTP in their solutions, powders, or crystals but exhibit significantly persistent RTP signals when embedded into the PVA matrix. Charge-transfer excited states were trapped by cofacial stacking in crystal, which blocks the intersystem crossing channels. In the PVA matrix, the allowed broad distribution of charge-transfer states covers the locally excited states, offering multiple intersystem crossing pathways via spin-vibronic orbit coupling. Consequently, efficient and persistent heavy-atom-free phosphors have been developed with the highest quantum yields of 7.7% and the longest lifetime of 2.3 s.

A Single Carbon-Dot System Enabling Multiple Stimuli Activated Room-Temperature Phosphorescence

Room-temperature phosphorescent carbon dots (RTPCDs) have attracted considerable interests due to their unique nanoluminescent characteristic with time resolution. However, it is still a formidable challenge to construct multiple stimuli-activated RTP behaviors on CDs. Since the address of this issue facilitates complex and high-regulatable phosphorescent applications, we here develop a novel strategy to achieve a multiple stimuli responsive phosphorescent activation on a single carbon-dot system (S-CDs), using persulfurated aromatic carboxylic acid as the precursor. The introduction of aromatic carbonyl groups and multiple S atoms can promote the intersystem crossing process to generate RTP characteristic of the produced CDs. Meanwhile, by introducing these functional surface groups into S-CDs, the RTP property can be activated by light, acid, and thermal stimuli in solution or in film state. In this way, multistimuli responsive and tunable RTP characteristics are realized in the single carbon-dot system. Based on this set of RTP properties, S-CDs is applied to photocontrolled imaging in living cells, anticounterfeit label, and multilevel information encryption. Our work will benefit the development of multifunctional nanomaterials together with extending their application scope.

Room temperature phosphorescence from natural wood activated by external chloride anion treatment

Producing afterglow room temperature phosphorescence (RTP) from natural sources is an attractive approach to sustainable RTP materials. However, converting natural resources to RTP materials often requires toxic reagents or complex processing. Here we report that natural wood may be converted into a viable RTP material by treating with magnesium chloride. Specifically, immersing natural wood into an aqueous MgCl₂ solution at room temperature produces so-called C-wood containing chloride anions that act to promote spin orbit coupling (SOC) and increase the RTP lifetime. Produced in this manner, C-wood exhibits an intense RTP emission with a lifetime of ~ 297 ms (vs. the ca. 17.5 ms seen for natural wood). As a demonstration of potential utility, an afterglow wood sculpture is prepared in situ by simply spraying the original sculpture with a MgCl₂ solution. C-wood was also mixed with polypropylene (PP) to generate printable afterglow fibers suitable for the fabrication of luminescent plastics via 3D printing. We anticipate that the present study will facilitate the development of sustainable RTP materials.

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.

Antibacterial Carbon Dots-Based Composites

The emergence and global spread of bacterial resistance to conventionally used antibiotics have highlighted the urgent need for new antimicrobial agents that might replace antibiotics. Currently, nanomaterials hold considerable promise as antimicrobial agents in anti-inflammatory therapy. Due to their distinctive functional physicochemical characteristics and exceptional biocompatibility, carbon dots (CDs)-based composites have attracted a lot of attention in the context of these antimicrobial nanomaterials. Here, a thorough assessment of current developments in the field of antimicrobial CDs-based composites is provided, starting with a brief explanation of the general synthesis procedures, categorization, and physicochemical characteristics of CDs-based composites. The many processes driving the antibacterial action of these composites are then thoroughly described, including physical destruction, oxidative stress, and the incorporation of antimicrobial agents. Finally, the obstacles that CDs-based composites now suffer in combating infectious diseases are outlined and investigated, along with the potential applications of antimicrobial CDs-based composites.

Water-borne, durable and multicolor silicon nanoparticles/sodium alginate inks for anticounterfeiting applications

Recently, water-borne fluorescent inks have attracted extensive attention in anti-counterfeiting applications due to their convenient implementation and eco-friendliness. However, due to poor service durability, the latent authorization information from the inks is easily damaged, and even disappears when encountering water. Moreover, most of the existing fluorescent inks are monochromic, toxic, and allergic to skin, thus are unsuitable for their sustainability during real-life applications. Herein, this work presents environment-friendly, durable, and multicolor fluorescent anti-counterfeiting silicon nanoparticles (SiNPs)/sodium alginate (SA) inks. The multicolor SiNPs are synthesized by a one-pot method with defined morphologies and optical properties. Subsequently, SA is employed as the binder to prepare the fluorescent inks with optimized rheological properties. Practicability results show that the SiNPs/SA inks not only exhibit excellent printability, but also impart authentic information with superior covert performance. More notably, spraying solution of calcium dichloride can further improve fluorescent fastnesses of the SiNPs/SA inks by ionic crosslinking.

Progression of Quantum Dots Confined Polymeric Systems for Sensorics

The substantial fluorescence (FL) capabilities, exceptional photophysical qualities, and long-term colloidal stability of quantum dots (QDs) have aroused a lot of interest in recent years. QDs have strong and wide optical absorption, good chemical stability, quick transfer characteristics, and facile customization. Adding polymeric materials to QDs improves their effectiveness. QDs/polymer hybrids have implications in sensors, photonics, transistors, pharmaceutical transport, and other domains. There are a great number of review articles available online discussing the creation of CDs and their many uses. There are certain review papers that can be found online that describe the creation of composites as well as their many different uses. For QDs/polymer hybrids, the emission spectra were nearly equal to those of QDs, indicating that the optical characteristics of QDs were substantially preserved. They performed well as biochemical and biophysical detectors/sensors for a variety of targets because of their FL quenching efficacy. This article concludes by discussing the difficulties that still need to be overcome as well as the outlook for the future of QDs/polymer hybrids.

Long-Lived Dynamic Room Temperature Phosphorescence from Carbon Dots Based Materials

As a type of room temperature phosphorescence (RTP) material, carbon dots (CDs) always show short lifetime and low phosphorescence efficiency. To counter these disadvantages, several strategies, such as embedding in rigid matrix, introducing of heteroatom, crosslink-enhanced emission, etc., are well developed. Consequently, lots of CDs-based RTP materials are obtained. Doping of CDs into various matrix is the dominant method for preparation of long-lived CDs-based RTP materials so far. The desired CDs@matrix composites always display outstanding RTP performances. Meanwhile, matrix-free CDs and carbonized polymer dots-based RTP materials are also widely developed. Amounts of CDs possessing ultra-long lived, multiple colored, and dynamic RTP emission are successfully obtained. Herein, the recent progress achieved in CDs-based RTP materials as well as the corresponding efficient strategies and emission mechanisms are summarized and reviewed in detail. Due to CDs-based RTP materials possess excellent chemical stability, photostability and low biological toxicity, they exhibit great application potential in the fields of anti-counterfeiting, data encryption, and biological monitoring. The application of the CDs-based RTP materials is also introduced in this review. As a promising functional material, development of long wavelength RTP emitting CDs with long lifetime is still challengeable, especially for the red and near-infrared emitting RTP materials.

Developing Carbon Dots with Room-Temperature Phosphorescence for the Dual-Signal Detection of Metronidazole

Room-temperature phosphorescent carbon dots (CDs) show the advanced property owing to their dual signal; howbeit, acquiring the efficient phosphorescence of CDs is still challengeable. Here, we proposed one type of CD doped with nitrogen through the microwave method, which exhibited the obvious blue fluorescence in aqueous solution and green phosphorescence immobilized on filter paper, while diethylenetriamine pentamethylene phosphonic acid provided the source of carbon and nitrogen. Importantly, introducing metronidazole (MNZ) into the CDs leads to their simultaneous decrease in both fluorescence and phosphorescence, and thus, we successfully established a dual-signal strategy for detecting MNZ. Likewise, this fluorescent detection showed the linear range of 2-200 μM and the phosphorescent way of 50-2000 μM. Meanwhile, the corresponding detection mechanism was also explored, and both the quenched fluorescence and phosphorescence of CDs were mainly due to the occurrence of the electron transfer and internal filtration effect between CDs and MNZ. Additionally, we employed these CDs as the fluorescent and phosphorescent inks for painting and information encryption.

In Situ Confining Citric Acid-Derived Carbon Dots for Full-Color Room-Temperature Phosphorescence

Room-temperature phosphorescence has received much attention owing to its potential applications in information encryption and bioelectronics. However, the preparation of full-color single-component-derived phosphorescent materials remains a challenge. Herein, a facile in situ confining strategy is proposed to achieve full-color phosphorescent carbon dots (CDs) through rapid microwave-assisted carbonization of citric acid in NaOH. By tuning the mass ratio of citric acid and NaOH, the obtained CDs exhibit tunable phosphorescence wavelengths ranging from 483 to 635 nm and alterable lifetimes from 58 to 389 ms with a synthesis yield of up to 83.7% (>30 g per synthesis). Theoretical calculations and experimental results confirm that the formation of high-density ionic bonds between cations and CDs leads to efficient afterglow emission via the dissociation of CD arrangement, and the evolution of the aggregation state of CDs results in redshifted phosphorescence. These findings provide a strategy for the synthesis of new insights into achieving and manipulating room-temperature phosphorescent CDs, and prospect their applications in labeling and information encryption.

Reduced Graphene Oxide Quantum Dot Light Emitting Diodes Fabricated Using an Ultraviolet Light Emitting Diode Photolithography Technique

Graphene quantum dots usually suffer from serious fluorescence quenching in aggregates and the solid state due to easy agglomeration and aggregation-induced quenching, which seriously restrict their practical applications. An ingenious strategy to kill three birds with one stone, the ultraviolet (UV) photolithography technique, was studied, and blue-emitting reduced graphene oxide quantum dot (rGOQD)-based light emitting diodes (LEDs) with efficient solid state emission were first fabricated using UV photolithography. First, rGOQDs were prepared by the in situ photoreduction of GOQDs by using the photoinitiator phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide with 395 nm UV LED exposure. Furthermore, rGOQD/photoresist patterns were prepared under the same conditions. Meanwhile, the in situ photoreduction of GO in the aforementioned photoresist to rGO was realized by UV photolithography to improve the conductivity of the rGOQD/photoresist films. Additionally, the in situ photoreduction of GOQDs in different surroundings was studied, with the results showing that GOQDs are more easily photoreduced in ionic liquids and that the photoluminescence spectrum obtained for rGOQDs exhibits a 70 nm blueshift with a narrow full-width at half-maximum compared to GOQDs.

Excitation energy mediated cross-relaxation for tunable upconversion luminescence from a single lanthanide ion

Precise control of energy migration between sensitizer ions and activator ions in lanthanide-doped upconversion nanoparticles (UCNPs) nowadays has been extensively investigated to achieve efficient photon upconversion. However, these UCNPs generally emit blue, green or red light only under fixed excitation conditions. In this work, regulation of the photon transition process between different energy levels of a single activator ion to obtain tunable upconversion fluorescence under different excitation conditions is achieved by introducing a modulator ion. The cross-relaxation process between modulator ion and activator ion can be controlled to generate tunable luminescence from the same lanthanide activator ion under excitation at different wavelengths or with different laser power density and pulse frequency. This strategy has been tested and proven effective in two different nanocrystal systems and its usefulness has been demonstrated for high-level optical encryption.

Here, the authors report tunable luminescence from a single lanthanide ion upon changing excitation conditions through co-doping an energy-modulator ion, thus adjusting the photon transition process of the lanthanide activator ion. Optical encryption has also been demonstrated as an application of this universal strategy.

Carbon Dots in Hydroxy Fluorides: Achieving Multicolor Long-Wavelength Room-Temperature Phosphorescence and Excellent Stability via Crystal Confinement

Carbon dots (CDs) have aroused widespread interest in the construction of room-temperature phosphorescent (RTP) materials. However, it is a great challenge to obtain simultaneous multicolor long-wavelength RTP emission and excellent stability in CD-based RTP materials. Herein, a novel and universal "CDs-in-YOHF" strategy is proposed to generate multicolor and long-wavelength RTP by confining various CDs in the Y(OH)_xF_3-x (YOHF) matrix. The mechanism of the triplet emission of CDs is related to the space confinement, the formation of hydrogen bonds and C-F bonds, and the electron-withdrawing fluorine atoms. Remarkably, the RTP lifetime of orange-emissive CDs-o@YOHF is the longest among the reported single-CD-matrix composites for emission above 570 nm. Furthermore, CDs-o@YOHF exhibited higher RTP performance at long wavelength in comparison to CDs-o@matrix (matrix = PVA, PU, urea, silica). The resulting CDs@YOHF shows excellent photostability, thermostability, chemical stability, and temporal stability, which is rather favorable for information security, especially in a complex environment.

Luminescent Composite Carbon/SiO2 Structures: Synthesis and Applications

Luminescent carbon nanostructures (CNSs) have attracted great interest from the scientific community due to their photoluminescent properties, structural features, low toxicity, and a great variety of possible applications. Unfortunately, a few problems hinder their further development. These include the difficulties of separating a mixture of nanostructures after synthesis and the dependence of their properties on the environment and the aggregate state. The application of a silica matrix to obtain luminescent composite particles minimizes these problems and improves optical properties, reduces photoluminescence quenching, and leads to wider applications. We describe two methods for the formation of silica composites containing CNSs: inclusion of CNSs into silica particles and their grafting onto the silica surface. Moreover, we present approaches to the synthesis of multifunctional particles. They combine the unique properties of silica and fluorescent CNSs, as well as magnetic, photosensitizing, and luminescent properties via the combination of functional nanoparticles such as iron oxide nanoparticles, titanium dioxide nanoparticles, quantum dots (QDs), and gold nanoclusters (AuNCs). Lastly, we discuss the advantages and challenges of these structures and their applications. The novelty of this review involves the detailed description of the approaches for the silica application as a matrix for the CNSs. This will support researchers in solving fundamental and applied problems of this type of carbon-based nanoobjects.

Endowing matrix-free carbon dots with color-tunable ultralong phosphorescence by self-doping

Color-tunable ultralong phosphorescence is urgently desired in optoelectronic applications. Herein, we report a new type of full-color-tunable ultralong phosphorescence carbon dots (CDs) without matrix-assistance by a self-doping method under ambient conditions. The phosphorescence color can be rationally tuned from blue to red by changing the excitation wavelength from 310 to 440 nm. The CDs exhibit an ultralong lifetime of up to 1052.23 ms at 484 nm. From the experimental data, we speculate that the excitation-dependent multi-color phosphorescence is attributed to the presence of multiple emitting centers related to carbonyl units. Given the unique color-tunability of CDs, we demonstrate their potential applications in information encryption, light detection ranging from UV to visible light and LED devices. This finding not only takes a step towards the fundamental design of full-color emissive materials, but also provides a broader scope for the applications of phosphorescent materials.

Confined-domain crosslink-enhanced emission effect in carbonized polymer dots

Revealing the photoluminescence (PL) origin and mechanism is a most vital but challenging topic of carbon dots. Herein, confined-domain crosslink-enhanced emission (CEE) effect was first studied by a well-designed model system of carbonized polymer dots (CPDs), serving as an important supplement to CEE in the aspect of spatial interactions. The "addition-condensation polymerization" strategy was adopted to construct CPDs with substituents exerting different degrees of steric hindrance. The effect of confined-domain CEE on the structure and luminescence properties of CPDs have been systematically investigated by combining characterizations and theoretical calculations. Such tunable spatial interactions dominated the coupling strength of the luminophores in one particle, and eventually resulted in the modulated PL properties of CPDs. These findings provide insights into the structural advantages and the PL mechanism of CPDs, which are of general significance to the further development of CPDs with tailored properties.

Carbon Dots with an Emission in the Near Infrared Produced from Organic Dyes in Porous Silica Microsphere Templates

Carbon dots (CDs) with an emission in the near infrared spectral region are attractive due to their promising applications in bio-related areas, while their fabrication still remains a challenging task. Herein, we developed a template-assisted method using porous silica microspheres for the formation of CDs with optical transitions in the near infrared. Two organic dyes, Rhodamine 6G and IR1061 with emission in the yellow and near infrared spectral regions, respectively, were used as precursors for CDs. Correlation of morphology and chemical composition with optical properties of obtained CDs revealed the origin of their emission, which is related to the CDs' core optical transitions and dye-derivatives within CDs. By varying annealing temperature, different kinds of optical centers as derivatives of organic dyes are formed in the microsphere's pores. The template-assisted method allows us to synthesize CDs with an emission peaked at 1085 nm and photoluminescence quantum yield of 0.2%, which is the highest value reported so far for CDs emitting at wavelengths longer than 1050 nm.

Photopatterning of Carbon Dots in Poly(vinyl alcohol) with Photoacid Generators

Carbon dots (CDs) have drawn considerable attention owing to their attractive photoluminescence, advantageous chemical tolerance, good biocompatibility, and so on. However, it remains challenging to tune their photoluminescence spatially and temporally due to their high photostability. Herein, a viable approach to in-situ dialing the photoluminescence of CDs by using light in the presence of a photoacid generator (PAG, e.g., diphenyliodonium hexafluorophosphate) is demonstrated. Fluorescence quenching occurs upon light irradiation due to the protonation of pyridine and amino nitrogen atoms of CDs according to X-ray photoelectron spectroscopy and cyclic voltammetry. As such, blue, green, and red color fluorescent patterns of CDs are ready to form in poly(vinyl alcohol) by light irradiation under photomask. These patterns not only show a controlled preservation time under room light, but also can be erased on demand by flood UV irradiation, which are promising for advanced anti-counterfeiting such as shelf-life based security and erasable encryption.

Cu(ii)-assisted self-assembly of dicyandiamide-derived carbon dots: construction inspired from chemical evolution and its H2O2 sensing application

In the rapid development of artificial nanomaterials comparable to biological enzymes, we propose herein a novel concept for the construction of functional materials inspired from chemical evolution.

White Light Afterglow in Carbon Dots Achieved via Synergy between the Room-Temperature Phosphorescence and the Delayed Fluorescence

Carbon dot (CD) based long-lived afterglow emission materials have attracted attention in recent years, but demonstration of white-light room-temperature afterglow remains challenging, due to the difficulty of simultaneous generation of multiple long-lived excited states with distinct chromatic emission. In this work, a white-light room-temperature long-lived afterglow emission from a CD powder with a high efficiency of 5.8% and Commission International de l'Eclairage (CIE) coordinates of (0.396, 0.409) is realized. The afterglow of the CDs originates from a synergy between the phosphorescence of the carbon core and the delayed fluorescence associated with the surface CN moieties, which is accomplished by matching the singlet state of the surface groups of the CDs with the long-lived triplet state of the carbon core, resulting in an efficient energy transfer. It is demonstrated how the long-lived afterglow emission of CDs can be utilized for fabrication of white light emitting devices and in anticounterfeiting applications.

Near-Infrared-Excited Multicolor Afterglow in Carbon Dots-Based Room-Temperature Afterglow Materials

Room-temperature afterglow (RTA) materials with long lifetime have shown tremendous application prospects in many fields. However, there is no general design strategy to construct near-infrared (NIR)-excited multicolor RTA materials. Herein, we report a universal approach based on the efficient radiative energy transfer that supports the reabsorption from upconversion materials (UMs) to carbon dots-based RTA materials (CDAMs). Thus, the afterglow emission (blue, cyan, green, and orange) of various CDAMs can be activated by UMs under the NIR continuous-wave laser excitation. The efficient radiative energy transfer ensured the persistent multicolor afterglow up to 7 s, 6 s, 5 s, and 0.5 s by naked eyes, respectively. Given the unusual afterglow properties, we demonstrated preliminary applications in fingerprint recognition and information security. This work provides a new avenue for the activation of NIR-excited afterglow in CDAMs and will greatly expand the applications of RTA materials.

Carbon Dot/Polymer Composites with Various Precursors and Their Sensing Applications: A Review

Carbon dots (CDs) have generated much interest because of their significant fluorescence (FL) properties, extraordinary photophysical attributes, and long-term colloidal stability. CDs have been regarded as a prospective carbon nanomaterial for various sensing applications because of their low toxicity, strong and broad optical absorption, high chemical stability, rapid transfer properties, and easy modification. To improve their functionality, CD/polymer composites have been developed by integrating polymers into CDs. CD/polymer composites have diversified because of their easy preparation and applications in sensing, optoelectronics, semiconductors, molecular delivery, and various commercial fields. Many review articles are available regarding the preparation and applications of CDs. Some review articles describing the production and multiple applications of the composites are available. However, no such article has focused on the types of precursors, optical properties, coating characteristics, and specific sensing applications of CD/polymer composites. This review aimed to highlight and summarize the current progress of CD/polymer composites in the last five years (2017–2021). First, we overview the precursors used for deriving CDs and CD/polymer composites, synthesis methods for preparing CDs and CD/polymer composites, and the optical properties (absorbance, FL, emission color, and quantum yield) and coating characteristics of the composites. Most carbon and polymer precursors were dominated by synthetic precursors, with citric acid and polyvinyl alcohol widely utilized as carbon and polymer precursors, respectively. Hydrothermal treatment for CDs and interfacial polymerization for CDs/polymers were frequently performed. The optical properties of CDs and CD/polymer composites were almost identical, denoting that the optical characters of CDs were well-maintained in the composites. Then, the chemical, biological, and physical sensing applications of CD/polymer composites are categorized and discussed. The CD/polymer composites showed good performance as chemical, biological, and physical sensors for numerous targets based on FL quenching efficiency. Finally, remaining challenges and future perspectives for CD/polymer composites are provided.