High production-yield solid-state carbon dots with tunable photoluminescence for white/multi-color light-emitting diodes

Carbon Dots: A Bright Future as Anticounterfeiting Encoding Agents

Counterfeit products and data vulnerability present significant challenges in contemporary society. Hence, various methods and technologies are explored for anticounterfeiting encoding, with luminescent tracers, particularly luminescent carbon dots (CDs), emerging as a notable solution. CDs offer promising contributions to product security, environmental sustainability, and the circular economy. This critical review aims to highlight the luminescence responsiveness of CDs to physical and chemical stimuli, achieved through nanoengineering their chemical structure. The discussion will delve into the various tunable luminescence mechanisms and decay times of CDs, investigating preferential excitations such as up-conversion, delayed fluorescence, fluorescence, room temperature phosphorescence, persistent luminescence, energy and charge transfer, as well as photo-chemical interactions. These insights are crucial for advancing anticounterfeiting solutions. Following this exploration, a systematic review will focus on the research of luminescent CDs' smart encoding applications, encompassing anticounterfeiting, product tracing, quality certification, and information encryption. Finally, the review will address key challenges in implementing CDs-based technology, providing specific insights into strategies aimed at maximizing their stability and efficacy in anticounterfeiting encoding applications.

Carbon Dots Derived from Non-Biomass Waste: Methods, Applications, and Future Perspectives

Carbon dots (CDs) are luminescent carbon nanoparticles with significant potential in analytical sensing, biomedicine, and energy regeneration due to their remarkable optical, physical, biological, and catalytic properties. In light of the enduring ecological impact of non-biomass waste that persists in the environment, efforts have been made toward converting non-biomass waste, such as ash, waste plastics, textiles, and papers into CDs. This review introduces non-biomass waste carbon sources and classifies them in accordance with the 2022 Australian National Waste Report. The synthesis approaches, including pre-treatment methods, and the properties of the CDs derived from non-biomass waste are comprehensively discussed. Subsequently, we summarize the diverse applications of CDs from non-biomass waste in sensing, information encryption, LEDs, solar cells, and plant growth promotion. In the final section, we delve into the future challenges and perspectives of CDs derived from non-biomass waste, shedding light on the exciting possibilities in this emerging area of research.

Polyvinylalcohol Composite Filled with Carbon Dots Produced by Laser Ablation in Liquids

Carbon dots (CDs), owing to their excellent photoluminescent features, have been extensively studied for physics preparation methods and for biomedical and optoelectronic device applications. The assessment of the applicability of CDs in the production of luminescent polymeric composites used in LEDs, displays, sensors, and wearable devices is being pursued. The present study reports on an original, environmentally friendly, and low-cost route for the production of carbon dots with an average size of 4 nm by laser ablation in liquid. Jointly, to prove the significance of the study for a wide range of applications, a free-standing flexible polyvinyl alcohol (PVA) composite containing photoluminescent carbon dots was manufactured. CDs were prepared using targets of porose charcoal with a density of 0.271 g/cm3 placed in phosphate-buffered saline (PBS) liquid solution and irradiated for 30 min by pulsed IR diode laser. The optical properties of the obtained suspension containing carbon dots were studied with UV-ViS and FTIR spectroscopies. The photoluminescence of the produced carbon dots was confirmed by the emission peak at 480 nm in the luminescence spectrum. A narrow luminescence band with a full width at half-maximum (FWHM) of less than 40 nm could be an asset in spectral emission analysis in different applications. Atomic force microscopy confirms the feasibility of manufacturing CDs in clean and biocompatible environments, paving the way for an easier and faster production route, crucial for their wider applicability.

Multi-color polymer carbon dots synthesized from waste polyolefins through phenylenediamine-assisted hydrothermal processing

The large accumulation and low recycling rates of polyolefin waste have posed a threat to the environment and human health. The shortage of chemical recycling methods for polyolefins strongly demands the development of new and sustainable treatment technologies for hydrocarbon plastics to improve their waste management. In this study, polyethylene (PE) and polypropylene (PP) were utilized for the preparation of multi-color polymer carbon dots (PCDs) via a two-step hydrothermal (HT) synthesis involving (i) thermo-oxidative degradation of polyolefins to precursors containing plentiful oxygen-based functional groups, and (ii) modification with phenylenediamine (PDA). The fluorescence of PCDs depends on the structure of isomeric PDA and PCDs modified by ortho-, meta-, and para-PDA emit blue, green, and yellow color fluorescence, respectively. The formation mechanism of PCDs, involving dehydrative condensation and amination of PE or PP-derived precursors by PDA, was proposed. The obtained PCDs were utilized for the detection and quantification of Fe3+ ions at ppm concentrations. The proposed strategy here aims to broaden the scope of the chemical recycling methods for polyolefin plastic waste as well as to develop a conversion route of polyolefin to value-added materials.

Colloidal Chiral Carbon Dots: An Emerging System for Chiroptical Applications

Chiral CDots (c-CDots) not only inherit those merits from CDots but also exhibit chiral effects in optical, electric, and bio-properties. Therefore, c-CDots have received significant interest from a wide range of research communities including chemistry, physics, biology, and device engineers. They have already made decent progress in terms of synthesis, together with the exploration of their optical properties and applications. In this review, the chiroptical properties and chirality origin in extinction circular dichroism (ECD) and circularly polarized luminescence (CPL) of c-CDots is briefly discussed. Then, the synthetic strategies of c-CDots is summarized, including one-pot synthesis, post-functionalization of CDots with chiral ligands, and assembly of CDots into chiral architectures with soft chiral templates. Afterward, the chiral effects on the applications of c-CDots are elaborated. Research domains such as drug delivery, bio- or chemical sensing, regulation of enzyme-like catalysis, and others are covered. Finally, the perspective on the challenges associated with the synthetic strategies, understanding the origin of chirality, and potential applications is provided. This review not only discusses the latest developments of c-CDots but also helps toward a better understanding of the structure-property relationship along with their respective applications.

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.

High SERS performance of functionalized carbon dots in the detection of dye contaminants

INTRODUCTION

The long-term overuse of malachite green (MG) has potential carcinogenic, teratogenic, and mutagenic effects. The functional nanocomposite is novel and challenging to construct and implement through surface enhanced Raman scattering (SERS) strategy to reveal the contributions in application.

OBJECTIVES

The novel Ag-CDs (carbon dots)-PBA (phenyl boric acid) nanocomposite was constructed by a facile route to detect toxic MG molecule with high SERS sensitivity and good uniformity.

METHODS

The enhanced substrate used for the detection of MG has been successfully constructed using PBA modulated Ag-CDs on a structured surface with rich binding sites.

RESULTS

The fabricated Ag-CDs-PBA substrate can be used to analyze various probe molecules exhibiting high sensitivity, good signal reproducibility, and excellent stability. The mechanism between components has been proved by calculations originating from the plasmonic Ag and active electronic transmission among the bridging CDs and PBA via the close spatial π-π effect. In addition, the accelerated separation of electron-hole pairs was triggered to further improve the SERS activity of the hybrid via a bidirectional charge transfer (CT) process. Significantly, the Ag-CDs-PBA system shows distinctive selectivity, in which PBA can hinder the interference of other species without specific hydroxyl groups.

CONCLUSION

Based on this deeper insight on plasmon-mediated mechanism, the SERS substrate was successfully practiced for quantitative determination in real water and fish samples. The strategy developed promises to be a new sensor technology and has great potential for environmental and food safety applications.

Unraveling fluorescent mechanism of biomass-sourced carbon dots based on three major components: Cellulose, lignin, and protein

The complexity of biomass components leads to significant variations in the performance of biomass-based carbon dots (CDs). To shed light on this matter, this study presents a comparative analysis of the fluorescence properties of CDs using pure cellulose, lignin, and protein as models. Three CDs showed different fluorescent properties, resulting from the structure difference and carbonization behavior in the hydrothermal. The relatively gentle thermal degradation of proteins allows the macromolecular structure of amino acids to be preserved. This preservation results in a more regular lattice structure, a larger sp2 domain size, and N-doping, which contribute to the highest quantum yield (QY) of 8.7% of the CDs. In contrast, cellulose undergoes more severe thermal degradation with large amounts of small molecules generated, resulting in the CDs with fewer surface defects, more irregular lattice structures, and lower QY. These results provide a guideline for the design of carbon dots from different biomass.

Surface Modification Functionalized Carbon Dots

Carbon dots (CDs) smaller than 10 nm constitute a new type of fluorescent carbon-based nanomaterial. They have attracted much attention owing to their unique structures and excellent photoelectric properties. Primitive CDs usually comprise carbon and oxygen and are synthesized in one step from various natural products or synthetic organic compounds, usually via microwave or hydrothermal methods. However, the uniformity of surface functional groups often make CDs lack the diversity of active sites required for specific applications. Therefore, the functionalization of CDs by specific groups is a powerful strategy for improving their photophysical and photochemical properties. This paper reviews surface modification strategies to overcome these shortcomings. Functionalizing CDs using covalent or non-covalent modification can give them unique properties and broaden their applicability.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Carbon Dot Based Multicolor Electroluminescent LEDs with Nearly 100% Exciton Utilization Efficiency

Carbon dots (CDs) are promising nanomaterials for next-generation lighting and displays due to their tunable bandgap, high photoluminescence quantum yield (PLQY), and high stability. However, the exciton utilization efficiency (EUE) of CD-based films can only reach 25%, fundamentally limiting their application in electroluminescent light-emitting diodes (LEDs). Improving the EUE is therefore of great significance. Herein, we developed composite films containing CDs and poly(9-vinylcarbazole) (PVK). The films were then used to construct a series of high-performance electroluminescent LEDs with tunable emission colors covering the blue to green regions as the concentration of CDs in the films increased, delivering a maximum external quantum efficiency and current efficiency of 2.62% and 5.11 cd/A, respectively. Theoretical calculations and experiments established that the excellent performance at low film PLQY was due to a hot exciton effect in the CDs, achieving nearly 100% EUE. This work provides new design strategies toward high-performance CD-based electroluminescent LEDs.

Ultra-Narrow-Bandwidth Deep-Red Electroluminescence Based on Green Plant-Derived Carbon Dots

Deep-red light-emitting diodes (DR-LEDs, >660 nm) with high color-purity and narrow-bandwidth emission are promising for full-color displays and solid-state lighting applications. Currently, the DR-LEDs are mainly based on conventional emitters such as organic materials and heavy-metal based quantum dots (QDs) and perovskites. However, the organic materials always suffer from the complicated synthesis, inferior color purity with full-width at half-maximum (FWHM) more than 40 nm, and the QDs and perovskites still suffer from serious problems related to toxicity. Herein, this work reports the synthesis of efficient and high color-purity deep-red carbon dots (CDs) with a record narrow FWHM of 21 nm and a high quantum yield of more than 50% from readily available green plants. Moreover, an exciplex host is further established using a polymer and small molecular blend, which has been shown to be an efficient strategy for producing high color-purity monochrome emission from deep-red CDs via Förster energy transfer (FET). The deep-red CD-LEDs display high color-purity with Commission Internationale de l'Eclairage (CIE) coordinates of (0.692, 0.307). To the best of the knowledge, this is the first report of high color-purity CD-LEDs in the deep-red region, opening the door for the application of CDs in the development of high-resolution light-emitting display technologies.

EGTA-Derived Carbon Dots with Bone-Targeting Ability: Target-Oriented Synthesis and Calcium Affinity

The bone-targeting mechanism of clinic bisphosphonate-type drugs, such as alendronate, risedronate, and ibandronate, relies on chelated calcium ions on the surface of the bone mineralized matrix for the treatment of osteoporosis. EGTA with aminocarboxyl chelating ligands can specifically chelate calcium ions. Inspired by the bone-targeting mechanism of bisphosphonates, we hypothesize that EGTA-derived carbon dots (EGTA-CDs) hold bone-targeting ability. For the target-oriented synthesis of EGTA-CDs and to endow CDs with bone targeting, we designed calcium ion chelating agents as precursors, including aminocarboxyl chelating agents (EGTA and EDTA) and bisphosphonate agents (ALN and HEDP) for the target-oriented synthesis of aminocarboxyl-derived CDs (EGTA-CDs and EDTA-CDs) and bisphosphonate-derived CDs (ALN-CDs and HEDP-CDs) with high synthetic yield. The synthetic yield of EGTA-CDs reached 87.6%. Aminocarboxyl-derived CDs and bisphosphonate-derived CDs retain the chelation ability of calcium ions and can specifically bind calcium ions. The chemical environment bone-targeting value coordination constant K and chelation sites of EGTA-CDs were 6.48 × 104 M-1 and 4.12, respectively. A novel method was established to demonstrate the bone-targeting capability of chelate-functionalized carbon dots using fluorescence quenching in a simulated bone trauma microenvironment. EGTA-CDs exhibit superior bone-targeting ability compared with other aminocarboxyl-derived CDs and bisphosphonate-derived CDs. EGTA-CDs display exceptional specificity toward calcium ions and better bone affinity than ALN-CDs, suggesting their potential as novel bone-targeting drugs. EGTA-CDs with strong calcium ion chelating ability have calcium ion affinity in simulated body fluid and bone-targeting ability in a simulated bone trauma microenvironment. These findings offer new avenues for the development of advanced bone-targeting strategies.

Three birds, one stone: Disinfecting and turning waste medical masks into valuable carbon dots for sodium hydrosulfite and Fe3+ detection enabled by a simple hydrothermal treatment

Disposable medical masks are widely used to prevent respiratory infections due to their ability to block virus particles from entering the human body. The coronavirus disease 2019 (COVID-19) pandemic highlighted the importance of medical masks, leading to their widespread use around the world. However, a large number of disposable medical masks have been discarded, some carrying viruses, which have posed a grave threat to the environment and people's health, as well as wasting resources. In this study, a simple hydrothermal method was used for the disinfection of waste medical masks under high-temperature conditions as well as for their transformation into high-value-added carbon dots (CDs, a new type of carbon nanomaterial) with blue-emissive fluorescence, without high energy consumption or environmental pollution. Moreover, the mask-derived CDs (m-CDs) could not only be used as fluorescent probes for sensing sodium hydrosulfite (Na₂S₂O₄), which is widely used in the food and textile industries but is seriously harmful to human health, but also be used for detecting Fe³⁺ which is harmful to the environment and human health due to its wide use in industries.

Plastic Waste-Derived Carbon Dots: Insights of Recycling Valuable Materials Towards Environmental Sustainability

Carbon dots (CDs) or carbon quantum dots (CQDs) have emerged as rising stars in the carbon family due to their diverse applications in various fields. CDs are spherical particles with a well-distributed size of less than 10 nm. Functional CDs are promising nanomaterials with low toxicity, low cost, and enormous applications in the field of bioimaging, optoelectronics, photocatalysis, and sensing. Plastic is non-biodegradable and hazardous to the environment, however extremely durable and used in abundance. During the COVID-19 pandemic, the use of plastic waste, particularly masks, goggles, face shields, and shoe cover, has increased tremendously. It needs to be recycled in a productive way as plastic wastes take hundreds or thousands of years to degrade naturally. The conversion of plastic waste into magnificent CDs has been reported as one of the key alternatives for environmental sustainability and socio-economic benefits. In this review, synthetic routes for the conversion of plastic wastes into CDs utilizing hydrothermal, solvothermal, pyrolysis, flash joule heating, and characterization of these CDs using different techniques, such as Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and transmission electron microscope, have been discussed. Furthermore, potential applications of these plastic-derived CDs in sensing, catalysis, agronomics, and LED lights are summarized herein.

Recent developments in carbon dots: a biomedical application perspective

Recently, newly developed carbon-based nanomaterials known as carbon dots (CDs) have generated significant interest in nanomedicine. However, current knowledge regarding CD research in the biomedical field is still lacking. An overview of the most recent development of CDs in biomedical research is given in this review article. Several crucial CD applications, such as biosensing, bioimaging, cancer therapy, and antibacterial applications, are highlighted. Finally, CD-based biomedicine's challenges and future potential are also highlighted to enrich biomedical researchers' knowledge about the potential of CDs and the need for overcoming various technical obstacles.

Construction of a ratiometric fluorescent probe for visual detection of urea in human urine based on carbon dots prepared from Toona sinensis leaves and 5-carboxyfluorescein

In this work, pH-sensitive blue fluorescent carbon dots (CDs) with high fluorescence quantum yield (17.24%) were synthesized by hydrothermal method using Toona sinensis leaves and ethylenediamine (EDA) as raw materials. The CDs can detect urea with a limit of detection (LOD) of 6.700 mmol L^-1. For more sensitive detection of urea, we constructed a ratiometric fluorescent probe (CDs@5-FAM) using CDs and 5-carboxyfluorescein (5-FAM). The CDs@5-FAM probe can rapidly and sensitively detect urea according to the changes of I₅₁₄/I₄₀₅, with LOD as low as 0.014 mmol L^-1. Furthermore, with the help of a smartphone and RGB analysis software, urea's visual intelligent detection was realized using a CDs@5-FAM probe. The method proposed in this paper is consistent with the standard method, which indicates that the pH-sensitive ratiometric fluorescent probe CDs@5-FAM is accurate and reliable for practical application. It provides a new way for rapid and visual detection of urea.

The Emerging Development of Multicolor Carbon Dots

As a relatively new type of fluorescent carbon-based nanomaterials, multicolor carbon dots (MCDs) have attracted much attention because of their excellent biocompatibility, tunable photoluminescence (PL), high quantum yield, and unique electronic and physicochemical properties. The multicolor emission characteristics of carbon dots (CDs) obviously depend on the carbon source precursor, reaction conditions, and reaction environment, which directly or indirectly determines the multicolor emission characteristics of CDs. Therefore, this review is the first systematic classification and summary of multiple regulation methods of synthetic MCDs and reviews the recent research progress in the synthesis of MCDs from a variety of precursor materials such as aromatic molecules, small organic molecules, and natural biomass, focusing on how different regulation methods produce corresponding MCDs. This review also introduces the innovative applications of MCDs in the fields of biological imaging, light-emitting diodes (LEDs), sensing, and anti-counterfeiting due to their excellent PL properties. It is hoped that by selecting appropriate adjustment methods, this review can inspire and guide the future research on the design of tailored MCDs, and provide corresponding help for the development of multifunctional MCDs.

Multisignal optical temperature-sensing properties of Eu3+ -doped NaYF4 nanoparticles

In this paper, the multisignal (different emissions/colours) temperature sensing of NaYF4 :Eu3+ nanoparticles is investigated, which is based on fluorescence intensity ratios (FIRs) between 5 D0 →7 FJ (J=1-4) and 5 D1 →7 FJ' emissions. The 5 D1 →7 FJ' (J'=0-2) emissions can be clearly observed due to the low photon energy of NaYF4 . Based on the FIRs between different 5 D0 →7 FJ and 5 D1 →7 FJ' emissions, higher absolute/relative temperature sensitivities are obtained. Compared with the FIR between whole 5 D0 →7 FJ and 5 D1 →7 FJ' emissions, the maximum value of Sa was improved from 0.27 K-1 to 5.02 K-1 and that of Sr was improved from 0.89%·K-1 to 1.27%·K-1 . Furthermore, the FIRs between different colours of emissions were investigated for the application of wide-range multicolour temperature sensing.

Preparation of Multicolour Solid Fluorescent Carbon Dots for Light-Emitting Diodes Using Phenylethylamine as a Co-Carbonization Agent

Carbon dots (CDs), as a new type of photoluminescent nanomaterial, have attracted extensive attention in various fields because of their unique luminescence properties. However, CDs will exhibit fluorescence quenching in the solid state or aggregate state, which limits their application. In this paper, a unique strategy is proposed to regulate solutions to achieve multicolour fluorescence of CDs in the solid state. We report the successful preparation of orange, green and blue solid fluorescent CDs using citric acid, urea and phenylethylamine as precursors and methanol, ethanol and water as solvents, respectively. The solid-state fluorescence of CDs may be caused by the linkage of the phenylethyl structure to the surface of CDs during formation, which effectively disperses the CDs and prevents π–π interactions between graphitized nuclei. Meanwhile, multicolour solid fluorescent CDs are realized by adjusting the solvent in the preparation process. Based on the excellent fluorescence properties of CDs, orange, green and blue light-emitting diodes (LEDs) are prepared. A white LED (WLED) can be obtained by mixing the three colours of solid fluorescent CDs, which shows the application potential of CDs in display lighting equipment.

Excitation-dependent perovskite/polymer films for ultraviolet visualization

Ultraviolet (UV) visualization has extensive applications in military and civil fields such as security monitoring, space communication, and wearable equipment for health monitoring in the internet of things (IoT). Due to their remarkable optoelectronic features, perovskite materials are regarded as promising candidates for UV light detecting and imaging. Herein, we report for the first time the excitation-dependent perovskite/polymer films with dynamically tunable fluorescence ranging from green to magenta by changing the UV excitation from 260 to 380 nm. And they still render dynamic multi-color UV light imaging with different polymer matrixes, halogen ratios, and cations of perovskite materials. The mechanism of its fluorescence change is related to the chloride vacancies in perovskite materials. A patterned multi-color ultraviolet visualization pad is also demonstrated for visible conversion of the UV region. This technique may provide a universal strategy for information securities, UV visualizations, and dynamic multi-color displays in the IoT.

Examining the effects of information and communications technology on green growth and environmental performance, socio-economic and environmental cost of technology generation: A pathway toward environment sustainability

Human capital and ICT have a significant role in determining human development. The impacts of ICT and human capital on green growth and environmental sustainability should be explored for sustainable economic development. This research contributes to the literature on the role of ICTs and human capital in the determination of green growth and environmental performance. Based on time-series data 1990-2019, the study intends to investigate the impact of ICTs and human capital on environmental and green growth performance for China. The study reports that ICTs tend to reduce CO2 emissions and improve green growth in the long-run. However, education reduces CO2 emissions in the long-run but does not produce any significant impact on green growth in the long-run. It is suggested that government should invest in environmental efficiency and environmental technologies simultaneously with human capital that could significantly contribute to pollution reduction. Lastly, policies to increase human capital should be implemented simultaneously with policies to promote ICTs contribution in order to confirm green growth and environmental protection.

Color Conversion Light-Emitting Diodes Based on Carbon Dots: A Review

This paper reviews the state-of-the-art technologies, characterizations, materials (precursors and encapsulants), and challenges concerning multicolor and white light-emitting diodes (LEDs) based on carbon dots (CDs) as color converters. Herein, CDs are exploited to achieve emission in LEDs at wavelengths longer than the pump wavelength. White LEDs are typically obtained by pumping broad band visible-emitting CDs by an UV LED, or yellow-green-emitting CDs by a blue LED. The most important methods used to produce CDs, top-down and bottom-up, are described in detail, together with the process that allows one to embed the synthetized CDs on the surface of the pumping LEDs. Experimental results show that CDs are very promising ecofriendly candidates with the potential to replace phosphors in traditional color conversion LEDs. The future for these devices is bright, but several goals must still be achieved to reach full maturity.

Breaking the Limitation of Elevated Coulomb Interaction in Crystalline Carbon Nitride for Visible and Near-Infrared Light Photoactivity

Most near-infrared (NIR) light-responsive photocatalysts inevitably suffer from low charge separation due to the elevated Coulomb interaction between electrons and holes. Here, an n-type doping strategy of alkaline earth metal ions is proposed in crystalline K⁺ implanted polymeric carbon nitride (KCN) for visible and NIR photoactivity. The n-type doping significantly increases the electron densities and activates the n→π* electron transitions, producing NIR light absorption. In addition, the more localized valence band (VB) and the regulation of carrier effective mass and band decomposed charge density, as well as the improved conductivity by 1-2 orders of magnitude facilitate the charge transfer and separation. The proposed n-type doping strategy improves the carrier mobility and conductivity, activates the n→π* electron transitions for NIR light absorption, and breaks the limitation of poor charge separation caused by the elevated Coulomb interaction.

Ionic Liquid-Assisted Fast Synthesis of Carbon Dots with Strong Fluorescence and Their Tunable Multicolor Emission

Conventional synthesis of carbon dots (CDs) mostly involves a hydrothermal or solvent-thermal reaction which needs relatively high temperature and pressure. In this work, ionic liquid is used to assist in fast synthesizing CDs with an ultrahigh photoluminescent quantum yield (98.5%) by heating at a low temperature (≤100 °C) and at atmospheric pressure. In addition, through this approach, tunable multicolor emissive CDs can be successfully achieved and used for preparing high-performance white light-emitting diodes. Theoretical computation proves that the activity of synthesis reaction can be significantly enhanced by ionic liquids. Density functional theory calculation reveals that the size and graphite nitrogen ratios of CDs have an effect on bandgap reduction, resulting in a redshift of the emission, which is in good agreement with the experimental results. This simple and promising approach for fast synthesis of tunable emissive CDs using ionic liquid affords the facilitation of CDs-based luminescent materials for fast manufacturing of functional devices.

Carbon-Based Nanomaterials for Sustainable Agriculture: Their Application as Light Converters, Nanosensors, and Delivery Tools

Nano-enabled agriculture is now receiving increasing attentions. Among the used nanomaterials, carbon-based nanomaterials are good candidates for sustainable agriculture. Previous review papers about the role of carbon-based nanomaterials in agriculture are either focused on one type of carbon-based nanomaterial or lack systematic discussion of the potential wide applications in agriculture. In this review, different types of carbon-based nanomaterials and their applications in light converters, nanosensors, and delivery tools in agriculture are summarized. Possible knowledge gaps are discussed. Overall, this review helps to better understand the role and the potential of carbon-based nanomaterials for nano-enabled agriculture.

F,N-Doped carbon dots as efficient Type I photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is a promising and emerging method for the treatment of cancer. Usually, Type II PDT is used in the clinic, and mainly involves three key elements: a photosensitizer, molecular oxygen and laser light. However, it is known that tumor tissue is deficient in oxygen molecules which is why Type I PDT is mostly preferred in the therapy of tumors in which the hypoxic tissue plays a major role. Fluorescent carbon dots (CDs) have shown great potential in cancer theranostics, acting as bioimaging agents and photosensitizers. Herein, we have synthesized novel kinds of fluorine and nitrogen co-doped carbon dots (F,NCDs) that emit bright green fluorescence under ultra-violet light. The F,NCDs have excellent water solubility and low cytotoxicity. They can generate hydroxyl radicals (˙OH) and superoxide anions (˙O2-) under LED light (400-500 nm, 15 mW cm-2) irradiation, making them ideal photosensitizers for Type I PDT. Furthermore, upon using the HepG2 cell line as an in vitro model, the F,NCDs exhibit a better cell imaging effect and higher PDT efficiency than the control sample of CDs without F and N doping. This work has illustrated that the F,NCDs are promising in achieving the image-guided PDT of cancers, usually in a hypoxia tumor microenvironment.

N,N-Dimethylformamide solvent assisted hydrothermal pretreatment of Chlorella for coproduction of sugar, nitrogenous compounds and carbon dots

Microalgae are considered as a promising alternative to fossil fuels due to their ease of cultivation, short growth cycle and no occupation of cultivated land. In this study, N,N-Dimethylformamide (DMF) solvent was employed to assist hydrothermal pretreatment of Chlorella for coproduction of sugar, nitrogenous compounds and carbon dots (CDs). The effect of pretreatment conditions on the composition and pyrolysis bio-oil distribution of hydrothermal solid residues as well as CDs characteristic were investigated by varying the temperature (180-220 ℃) and reaction time (1-9 h). The results showed that pretreated residues had higher cellulose. And the yield of sugar and N-contained compounds reached 41.59% and 63.57% in the pyrolysis bio-oil of pretreated algae residues, respectively. Moreover, CDs obtained from hydrothermal solution fluoresced red under 365 nm excitation. The paper provides a new method for the complete utilization of microalgae.

Waste to white light: a sustainable method for converting biohazardous waste to broadband white LEDs

The Covid-19 pandemic has generated a lot of non-degradable biohazardous plastic waste across the globe in the form of disposable surgical and N95 masks, gloves, face shields, syringes, bottles and plastic storage containers. In the present work we address this problem by recycling plastic waste to single system white light emitting carbon dots (CDs) using a pyrolytic method. The synthesized CDs have been embedded into a transparent polymer to form a carbon dot phosphor. This CD phosphor has a broad emission bandwidth of 205 nm and is stable against photo degradation for about a year. A white LED with CRI ∼70 and CIE co-ordinates of (0.25, 0.32) using the fabricated CD phosphor is reported. Further our phosphor is scalable and is environmentally sustainable, and will find wide application in next generation artificial lighting systems.

Recycling of plastic waste to white LEDs.

Highly stable and bright blue light-emitting diodes based on carbon dots with a chemically inert surface

The manufacture of blue light-emitting diodes (LEDs) has always been a tough problem to solve in the display and illumination fields. Inorganic/organic semiconductors and carbon dots (CDs) with a wide band gap still face obstacles such as a low external quantum efficiency (EQE) and poor stability. Herein, we synthesized highly stable and blue emission CDs with a chemically inert surface, and the photoluminescence (PL) peak (in ultra-pure water) of which is located at 446 nm with an absolute PL quantum yield (PLQY) of 26.4%. The LEDs based blue emission CDs exhibit an electroluminescence (EL) peak located at 456 nm and a high brightness of 223 cd m^-2 with an EQE of 0.856%. The Commission Internationale del'Eclairage (CIE) coordinates are located at (0.21, 0.23) and the device lifetime with 65% brightness (T ₆₅) reaches over 217 h because of the chemically inert surface of the CDs. The results mean the devices are the most stable CDs-LEDs reported to date. This work represents a novel route for the preparation of low cost, highly stable and very bright CDs-LEDs with a short wavelength emission.

Self-quenching-resistant solid-state carbon dots for mechanism and applications

Solid-state carbon dots (SCDs) have been widely investigated by scholars owing to their stability, environmental friendliness, and their good optical properties. The current studies on carbon dots (CDs) are mainly focused on the solutions of CDs, while the researches on SCDs are relatively few in comparison. Nowadays, the fabrication and design of high-performance SCDs have attracted much interest. However, due to resonance energy transfer and π-π interactions, CDs undergo aggregation-induced quenching (ACQ) phenomena. This poses an obstacle to the acquisition of SCDs and affects their luminescence performance. Publications of the past 5 years are reviewed on how to suppress the ACQ phenomenon and improve the fluorescence and phosphorescence emission of CDs (Ref. 87) and about the mechanism of achieving the luminescence of SCDs. Then, the applications of SCDs in the fields of luminescent devices, anti-counterfeiting, and detection are outlined. The concluding section analyzes the current challenges faced by SCDs and provides an outlook. Mechanism of photoluminescence from solid state carbon dots.

Upcycling of exhausted reverse osmosis membranes into value-added pyrolysis products and carbon dots

Polymeric reverse osmosis (RO) membranes are widely used worldwide for production of fresh water from various sources, primarily ocean desalination. However, with limited service life, exhausted RO membrane modules often end up as plastic wastes disposed of predominantly by landfilling. It is imperative to find a feasible way to upcycle end-of-life RO membrane modules into valuable products. In this paper, the feasibility of RO membrane recycling via pyrolysis and subsequent conversion of resulting char into carbon dots (CDs) through H₂O₂-assisted hydrothermal method was investigated. RO membrane module pyrolysis at 600 °C produced oil (28 wt%), non-condensable gas (17 wt%), and char (22 wt%). While oil and gas can serve as fuel and chemical feedstock due to rich hydrocarbon content, char was found a suitable precursor for the synthesis of functional CDs. The resulting CDs doped with N (4.8%) and S (1.8%) exhibited excellent water dispersibility, narrow size distribution of 1.3-6.8 nm, high stability, and strong blue fluorescence with a quantum yield of 6.24%. CDs demonstrated high selectivity and sensitivity towards Fe³⁺ in the range of 0-100 μM with the limit of detection of 2.97 μM and were capable of determining Fe³⁺ in real water samples (tap water and pond water).