Tricolor White-Light-Emitting Carbon Dots with Multiple-Cores@Shell Structure for WLED Application

Phenanthroline Derived N-Doped Carbon Dots as Robust Metal-Free Photocatalysts for PET-RAFT Polymerization and Polymerization-Induced Self-Assembly

Metal-free organic photocatalysts for photo-mediated reversible deactivation radical polymerization (photo-RDRP) are witnessed to make increasing advancement in the precise synthesis of polymers. However, challenges still exist in the development of high-efficiency and environmentally sustainable carbon dots (CDs)-based organocatalysts. Herein, N-doped CDs derived from phenanthroline derivative (Aphen) are prepared as metal-free photocatalysts for photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The introduction of phenanthroline structure enhances the excited state lifetime of CDs and expands the conjugated length of their internal structure to enable the light-absorption to reach green light region, thereby enhancing photocatalytic activity. The as-designed CDs exhibit unprecedented photocatalytic capacity in photopolymerization even in large-volume reaction (100 mL) with high monomer conversion and narrow polymer dispersity (Mw/Mn < 1.20) under green light. The photocatalytic system is compatible with PET-RAFT polymerization of numerous monomers and the production of high molecular weight polyacrylate (Mn >250 000) with exquisite spatiotemporal control. Above results confirm the potential of CDs as photocatalyst, which has not been achieved with other CDs catalysts used in photo-RDRP. In addition, the construction of fluorescent polymer nanoparticles using CDs as both photocatalyst and phosphor through photoinitiated polymerization-induced self-assembly (Photo-PISA) technology is successfully demonstrated for the first time.

Red-Emissive Center Formation within Carbon Dots Based on Citric Acid and Formamide

The formation of red-emissive optical centers in carbon dots based on citric acid and formamide was investigated by varying the synthesis parameters with focus on finding optimal─necessary and sufficient─amount of precursors to decrease byproduct amount and to increase the chemical yield of red-emissive carbon dots. The emission is observed at 640 nm excited at 590 nm and quantum yield reaches up 19%. A high chemical yield of carbon dots of 26% was achieved at an optimal molar ratio of citric acid to formamide of 1:4.

Synthesis Strategies, Optical Mechanisms, and Applications of Dual-Emissive Carbon Dots

Tuning the optical properties of carbon dots (CDs) and figuring out the mechanisms underneath the emissive phenomena have been one of the most cutting-edge topics in the development of carbon-based nanomaterials. Dual-emissive CDs possess the intrinsic dual-emission character upon single-wavelength excitation, which significantly benefits their multi-purpose applications. Explosive exploitations of dual-emissive CDs have been reported during the past five years. Nevertheless, there is a lack of a systematic summary of the rising star nanomaterial. In this review, we summarize the synthesis strategies and optical mechanisms of the dual-emissive CDs. The applications in the areas of biosensing, bioimaging, as well as photoelectronic devices are also outlined. The last section presents the main challenges and perspectives in further promoting the development of dual-emissive CDs. By covering the most vital publications, we anticipate that the review is of referential significance for researchers in the synthesis, characterization, and application of dual-emissive CDs.

Superior white electroluminescent devices using nitrogen-doped carbon dots/TiO2nanorods heterostructures

Nitrogen-doped carbon dots (NCDs), exhibiting strong yellow emission in aqueous solution and solid matrices, have been utilized for fabricating heterostructure white electroluminescence devices. These devices consist of nitrogen-doped carbon dots as an emissive layer sandwiched between an organic hole transport layer (PEDOT:PSS) and an array of rutile TiO2nanorods, acting as an electron transport layer. Under an applied forward bias of 5 V, the device exhibits broadband electroluminescence covering the wavelength range of 390-900 nm, resulting in pure white light emission characteristics at room temperature. The result demonstrates the successful fabrication of all solution-processed, low-cost, eco-friendly NCDs-based LEDs with CIE (Commission Internationale d'Éclairage) coordinate of (0.31, 0.34) and color rendering index (CRI) > 90, which are close to ideal white light emission characteristics. The device functionalities are achieved based on defect-related NIR emission from TiO2nanorods array and visible emission from nitrogen-doped carbon dots. This result paves a new opportunity to develop low-cost, solution-processed nitrogen-doped carbon dots based on warm White light emitting diodes with high CRI for large-area display and lighting applications.

Construction of composite films using carbon nanodots for blocking ultraviolet light from the Sun

Carbon nanodots (CNDs) which demonstrate concentration-dependent emission and have a photoluminescence quantum yield of 45% were designed. Transparent CND-containing composite films (CND-films), obtained by combining the CNDs with polyvinyl alcohol in different proportions, were shown to block the UV component of sunlight. Whereas the pure PVA film could not block UV light, the ability of CND-films to block UV light could be adjusted by altering the proportion of CNDs in the film. The larger the proportion of CNDs, the greater the extent of UV blocking. CND-film containing 32 wt% CNDs completely blocked UV light (≤400 nm) from sunlight, without affecting the transmission of visible light (>800 nm). The ability of the CND-films to block the UV component of sunlight was investigated using a commercially available UV-induced color change card, which confirmed that the capacity of the CND-films to block UV light could be adjusted by altering the proportion of CNDs in the film. This study shows that CNDs with concentration-dependent long wavelength emission characteristics can be used as optical barrier units for the preparation of materials to block high-energy short wavelength light.

Single-particle dispersion of carbon dots in the nano-hydroxyapatite lattice achieving solid-state green fluorescence

Carbon dots (CDs), as new carbon nanomaterials, have potential applications in multiple fields due to their superior optical properties, good biocompatibility, and easy preparation. However, CDs are typically an aggregation-caused quenching (ACQ) material, which has a huge limitation on the practical application of CDs. To solve this problem, in this paper, CDs were prepared by the solvothermal method using citric acid and o-phenylenediamine as precursors and dimethylformamide as solvent. Then using CDs as nucleating agents, solid-state green fluorescent CDs were synthesized by in situ growth of nano-hydroxyapatite (HA) crystals on the surface of CDs. The results show that CDs are stably dispersed single-particlely in the form of bulk defects in the nano-HA lattice matrices with a dispersion concentration of 3.10%, and solid-state green fluorescence of CDs is achieved with a stable emission wavelength peak position near 503 nm, which provides a new solution to the ACQ problem. CDs-HA nanopowders were further used as LED phosphors to obtain bright green LEDs. In addition, CDs-HA nanopowders showed excellent performance in cell imaging (mBMSCs and 143B) applications, which provides a new scheme for further applications of CDs in the field of cell imaging and even in vivo imaging.

A colorimetric and fluorometric dual-mode carbon dots probe derived from phenanthroline precursor for the selective detection of Fe2+ and Fe3

Iron's metabolism is heavily involved in the regulation of redox balance for cell functions, however, the simultaneous monitoring of Fe^2+/3+ concentration is still a great challenge due to their transitional nature in biological systems. A novel type of carbon dots (CDs) was synthesized by solvothermal treatment with 5-amino-1,10-phenanthroline (Aphen) and salicylic acid as precursors, and the resulting targeted CDs (T-CDs) were used to simultaneously detect Fe²⁺ and Fe³⁺. Comprehensive experimental characterizations revealed that the strong binding affinity of Aphen moiety to Fe²⁺ leads to the formation of rigid T-CDs aggregates, which causes a substantial enhancement of fluorescence intensity, whereas Fe³⁺ could cause the fluorescence quenching of T-CDs due to the oxidation-reduction induced electron transfer. These different fluorescence responses allow T-CDs to sensitively differentiate Fe²⁺ from Fe³⁺, and give the limit of detection (LOD) of 1.78 and 2.78 μM for Fe²⁺ and Fe³⁺, respectively. Furthermore, the Aphen dominated structure endows the T-CDs with a colorimetric response to Fe²⁺ with a LOD of 0.13 μM, which is very different from Fe³⁺. Thus, the dynamic changes of Fe²⁺ and Fe³⁺ in solution can be accurately monitored by T-CDs within the total iron concentration of 50 μM, which is probably the most sensitive dual-mode probe reported so far. In addition, this probe is successfully applied to detect the Fe^2+/3+ concentration in cells, demonstrating a huge application potential in the sensing of the dynamic equilibrium of these important transition metals during the cell metabolism or stimulated process. The dynamic changes of Fe²⁺ and Fe³⁺ in solution can be accurately monitored by carbon dots based on the colorimetric and fluorometric dual-mode.

One-Pot Three Carbon Dots with Various Lifetimes Rooted in Different Decarboxylation Degrees for Matrix-Free, Anti-Oxygen, and Time-Resolved Information Encryption and Cellular Imaging

Activating long-lived room temperature phosphorescence (RTP) in the aqueous environment and thus realizing matrix-free, anti-oxygen, and time-resolved information encryption and cellular imaging remain a great challenge. Here, we fabricated three types of carbon dots (C-dots), i.e., fluorescent C-dots (F-C-dots) and two types of phosphorescent C-dots denoted as Pw-C-dots and Py-C-dots by a one-pot strategy. Their formation was attributed to the difference in the decarboxylation degree at high temperatures using trimesic acid (TMA) as a sole precursor. Unexpectedly, the yield reached as high as ∼92%, and the proportions were ∼27% for F-C-dots, ∼17% for Pw-C-dots, and ∼56% for Py-C-dots. These nanomaterials could help implement carbon peaking and carbon neutrality. Both green RTP of the two C-dots resulted from the small energy gap (ΔEST). These two RTP C-dots had a long lifetime of over 270 ms with a relatively high quantum yield (4.5 and 6.2%). They exhibited excellent photostability and anti-photobleaching performances. The dry and wet powders of the RTP C-dots were applied to high-level information encryption. The lifelike patterns were greatly different from those of the original ones and could last for several seconds to the naked eye, demonstrating that the RTP C-dots could be potentially employed as anti-oxygen and time-resolved contrast reagents. Most significantly, the cellular imaging experiments showed that the biofriendly PVP-coated Py-C-dots could localize at lysosomes and sustain hundreds of milliseconds. This approach not only pioneers a time-resolved lysosome localization model but also opens up a promising door for anti-oxygen and time-resolved RTP cytoimaging.

Facile synthesis of graphene quantum dots with red emission and high quantum yield

Preparation of GQDs for application in cell imaging.

Assembly of Core/Shell Nanospheres of Amorphous Hemin/Acetone-Derived Carbonized Polymer with Graphene Nanosheets for Room-Temperature NO Sensing

Implementing parts per billion-level nitric oxide (NO) sensing at room temperature (RT) is still in extreme demand for monitoring inflammatory respiratory diseases. Herein, we have prepared a kind of core-shell structural Hemin-based nanospheres (Abbr.: Hemin-nanospheres, defined as HNSs) with the core of amorphous Hemin and the shell of acetone-derived carbonized polymer, whose core-shell structure was verified by XPS with argon-ion etching. Then, the HNS-assembled reduced graphene oxide composite (defined as HNS-rGO) was prepared for RT NO sensing. The acetone-derived carbonized polymer shell not only assists the formation of amorphous Hemin core by disrupting their crystallization to release more Fe-N₄ active sites, but provides protection to the core. Owing to the unique core-shell structure, the obtained HNS-rGO based sensor exhibited superior RT gas sensing properties toward NO, including a relatively higher response (R_a/R_g = 5.8, 20 ppm), a lower practical limit of detection (100 ppb), relatively reliable repeatability (over 6 cycles), excellent selectivity, and much higher long-term stability (less than a 5% decrease over 120 days). The sensing mechanism has also been proposed based on charge transfer theory. The superior gas sensing properties of HNS-rGO are ascribed to the more Fe-N₄ active sites available under the amorphous state of the Hemin core and to the physical protection by the shell of acetone-derived carbonized polymer. This work presents a facile strategy of constructing a high-performance carbon-based core-shell nanostructure for gas sensing.

Ultra-Broadband Random Laser and White-Light Emissive Carbon Dots/Crystal In-Situ Hybrids

The continuous white-light emission of carbon dots (CDs) can be applied to producing multicolor laser emissions by one single medium. Meanwhile, the solid-state emission greatly contributes to its practical application. In this work, a strategy to realize the in-situ hybridization of silane-functionalized CDs (SiCDs) and 1,3,5-benzenetricarboxylic acid trimethyl ester (Et3BTC) by a one-pot solvothermal method is reported. Significantly, the SiCDs/Et3BTC hybrid crystals exhibit ultra-broadband random laser emission over the near ultraviolet-visible region under 265 nm nanosecond pulsed laser excitation. The wavelength region of laser emission is achieved from 315 to 600 nm within an emission band of CDs-based materials. It is worth noting that the wavelength range of the laser is wider than the previously reported works. It is proposed that the continuous white-light emission of SiCDs caused by multiple fluorescence centers mainly gives rise to the broadband random laser emission. Moreover, the crystals are conducive to forming resonance and realizing solid-state laser emission. This in-situ method is expected to enable a more convenient, cheaper, and greener approach to prepare luminescent hybrids for application in multicolor laser displays, multi-level laser anti-counterfeiting, supercontinuum light sources, and so on.

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.

Tunable multimodal printable up-/down-conversion nanomaterials for gradient information encryption

Phosphor-based security techniques have received widespread attention because they can rely on fascinating optical properties (including multicolor emission and various luminous categories) to meet information protection requirements. Carbon dots (CDs) with multicolor fluorescence (FL) and room-temperature phosphorescence (RTP) show enormous potential in advanced information encryption, yet the achievement of tunable multimodal printable CDs confronts numerous challenges. Herein, liquid CDs with color-tunable properties ranging from blue to red are obtained, and the decay time-tunable RTPs of powdered CDs are achieved with a post-treatment of urea in an o-phenylenediamine/H₂O/H₃PO₄ system. Based on various security inks, anti-counterfeiting patterns with multilevel security strength are produced through screen printing technology. Color-tunable security patterns are obtained based on different security inks containing multicolor liquid CDs. The security strength can be boosted by combining the color-tunable properties and dual-mode luminescence of FL and RTP. Furthermore, higher-level anti-counterfeiting is achieved by introducing near-infrared induced upconversion luminescence phosphors into CDs systems. The excellent security performance of gradient information encryption shows that the proposed strategy establishes superior coding capacity for advanced information encryption and provides a good reference for cutting-edge research.

Hydrothermal Synthesis of High-Yield Red Fluorescent Carbon Dots with Ultra-Narrow Emission by Controlled O/N Elements

Red fluorescent carbon dots (r-CDs) with narrow dual emissions (600 nm and 658-683 nm, full width at half-maximums (FWHMs) of 20 nm and 30 nm), fluorescence quantum yield of 41.0%, and yield of 83.3% are prepared by hydrothermal method using o-phenylenediamine as precursor and inorganic oxidant as yield enhancer, and they have graphite nitrate-like structures. The long-wavelength side emission is aggregation-induced emission (AIE). A logarithmic relationship between the AIE wavelength (y) and the concentration (x) (y = 8.853ln(x) + 688.53, R = 0.998) is found. This regularity and the high monochromaticity of AIE are related to the existence of highly ordered structures proved by X-ray diffraction. Its intrinsic emission (FWHM: 20 nm) is the narrowest among the r-CDs prepared by hydrothermal method. The reason is that the decrease of oxygen content makes the FWHMs become narrow, and the decrease of the pyridine nitrogen content and the increase of pyrrole nitrogen content make them narrower further. The Fourier-transform infrared spectra and control experiment prove that oxidative polymerization is a necessary preparation step. The linear relationship between the amount of the oxidant and the CDs yield indicates that the yield can be increased only by increasing the conversion rate of the polymerization process.

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.

Probing the emission dynamics in nitrogen doped carbon dots by reversible capping with mercury (II) through surface chemistry

In this study, the mechanistic insight and emission dynamics have been explored of size dependent nitrogen doped carbon quantum dots (namely 3A,3B & 3C) with toxic metal Hg2+ ions via...

Structural Engineering toward High Monochromaticity of Carbon Dots-Based Light-Emitting Diodes

Monochromaticity for light-emitting diodes (LEDs) is an important parameter. However, carbon dots-based light-emitting diodes (CDs-LEDs) usually suffer from broad emission, which limits the development of this material. In this work, high-quality carbon dots (CDs) with a quantum yield of 16.2% were synthesized. When they were mixed with poly(N-vinyl carbazole) (PVK) to form a homogeneous film, the solid-state fluorescence of CDs was realized. After fabrication and systematic optimization of the device, the full width at half-maximum (fwhm) of EL spectra could be narrowed to 64 nm in comparison with the fwhm of 77 nm for PL, demonstrating that structural engineering is an effective approach for improving the color purity of CDs-LEDs. Meanwhile, the performance of the devices is improving. The obtained CDs-LEDs display high monochromaticity with a maximum luminance of 681 cd/m². This work provides a new way to optimize the monochromaticity and performance of CDs-LEDs.

Sensitive ratiometric fluorescence probe based on chitosan carbon dots and calcein for Alkaline phosphatase detection and bioimaging in cancer cells

Alkaline phosphatase (ALP) is a commonly used marker in clinical practice, and this enzyme is a key indicator for diagnosing various diseases. In this study, we describe the development of a reliable and novel fluorescent assay for ALP detection based on chitosan carbon dots (C-CDs, peak emission, 412 nm) and calcein (peak emission, 512 nm). In the presence of Eu³⁺ (which binds calcein), the fluorescence intensity of calcein is quenched. Utilizing the ALP-triggered generation of phosphate ions (PO₄^3-) from the substrate p-nitrophenyl phosphate (pNPP), the Eu³⁺ ions bind PO₄^3- (which shows a higher affinity toward Eu³⁺ than calcein), and the fluorescence of calcein is recovered. As a consequence, C-CDs fluorescence is decreased by inner filter effect (IFE). Exploiting these changes in the fluorescence intensity ratio of C-CDs and calcein, we developed a high sensitivity, accurate, and easily synthesized ratiometric fluorescence probe. Our novel fluorescent bioassay demonstrates good linear relationship in the 0.09-0.8 mU mL^-1 range, with a low detection limit of 0.013 mU mL^-1. The excellent applicability of this novel assay in HepG2 cells and human serum samples demonstrates that our novel method has excellent biomedical research and disease diagnosis prospects.

Red, green, and blue light-emitting carbon dots prepared from o-phenylenediamine

Carbon dots (CDs), as the most important type of carbon-based material, have been widely used in many fields because of their excellent properties. In particular, multicolor fluorescent CDs with high photoluminescence quantum yield are the focus of active research. Herein, red, green and blue CDs (RGB CDs) were successfully synthesized by a solvothermal method from o-phenylenediamine under different reaction conditions. The RGB-CDs have stable optical properties and significant photoluminescence characteristics. Structural and elemental analyses propose a conjugated structure and the surface state of the CDs as the main causes for the different color emission of RGB-CDs. In addition, a white fluorescent CD solution was prepared by mixing these multicolor fluorescent CDs in appropriate proportions.

Aluminum-Based Surface Polymerization on Carbon Dots with Aggregation-Enhanced Luminescence

Aggregation-induced luminescence quenching of carbon nanodots (CDs) is the main obstacle for their applications in solid-state light emitting devices. Herein, we developed a one-step synthesis of solid-state emissive CDs with surface aluminum-based polymerization by adding AlCl₃ in citric acid and urea via a microwave-heating dehydration process. Due to the strong coordination ability of Al ions with N and O atoms, considerable steric hindrance of Al-based cross-linked polymerization was introduced on the surface of the CDs, which not only avoided aggregation of the green emissive carbon cores but also facilitated efficient energy transfer from the blue emissive polymerized surface to the green emissive carbon cores in aggregates, leading to enhanced green emissions with a photoluminescence quantum yield (PLQY) of 72.7% in the solid state.

Lifetime-Engineered Carbon Nanodots for Time Division Duplexing

Optical multiplexing attracts considerable attention in the field of information encryption, optical probe, and time-resolved bioimaging. However, the optical multiplexing based on rare-earth nanoparticles suffers from heavy metal elements and relatively short lifetimes; sophisticated facilities are thus needed. Herein, time division duplexing based on eco-friendly carbon nanodots (CNDs) with manipulative luminescence lifetimes is demonstrated. In a single green color emission channel, the luminescence lifetimes of the CNDs can be manipulated from nanosecond level to second level by introducing water, while the lifetime of the CNDs confined by a silica shell stays. Time division duplexing based on the CNDs and CNDs@silica with distinct lifetimes is realized and spatio-temporal overlapping information is thus resolved. High-level information encryption using the time division duplexing technology is realized. This work may promise the potential applications of CNDs in multi-lifetime channels biological imaging, high-density information storage, and anti-counterfeiting.

Mussel-inspired polydopamine-encapsulated carbon dots with dual emission for detection of 4-nitrophenol and Fe3

Carbon dots (CDs) with excellent optical properties are widely used in biomedicine, fluorescence sensing, and light-emitting diodes (LEDs). However, it is still a challenge to prepare CDs that can stably emit red fluorescence in the water environment. In this study, polydopamine-encapsulated luminescent carbon dots (CDs@PDA) with an encapsulating structure were synthesized at room temperature from p-phenylenediamine-derived red-light CDs as the core and using mussel-inspired chemical properties of polydopamine (PDA). In the binary system of water:ethanol = 1: 3 (volume ratio), the as-prepared CDs@PDA had a dual emission of ultraviolet light (330 nm) and red light (640 nm) with the fluorescence quantum yields of 8.0 and 15.5%, respectively, at the same time under 285 nm light excitation. The as-prepared CDs@PDA could be directly used for fluorescence selective sensing of 4-nitrophenol (4-NP) and Fe³⁺ through simultaneously quenching of ultraviolet and red fluorescence based on the internal filtration effect mechanism with detection limits of 3.44 and 3.75 μM, respectively. This research showed that PDA-coated CDs can significantly improve the photoluminescence stability of CDs with new optical features. This means that the encapsulated structure of mussel chemistry is very helpful for expanding the application range of CDs in the water environment.

Biomass-Based Polymer Nanoparticles With Aggregation-Induced Fluorescence Emission for Cell Imaging and Detection of Fe3+ Ions

Polymeric nanoparticles, which show aggregation-induced luminescence emission, have been successfully prepared from larch bark, a natural renewable biomass resource, in a simple, rapid ultrasonic fragmentation method. The structure, element, particle size and molecular weight distribution of larch bark extracts (LBE) were studied by FTIR, XPS, TEM, XRD and linear mode mass spectrometry, respectively. LBE was found containing large numbers of aromatic rings, displaying an average particle size of about 4.5 nm and mainly presenting tetramers proanthocyanidins. High concentration, poor solvent, low temperature and high viscosity restricted the rotation and vibration of the aromatic rings in LBE, leading to the formation of J-aggregates and enhancing the aggregation-induced fluorescence emission. LBE possessed good resistance to photobleaching under ultraviolet light (200 mW/m²). Cytotoxicity experiments for 24 h and flow cytometry experiments for 3 days proved that even the concentrations of LBE as high as 1 mg/mL displayed non-toxic to MG-63 cells. Therefore, LBE could be employed for MG-63 cell imaging, with similar nuclear staining to the DAPI. The effects of different metal ions on the fluorescence emission intensity of LBE were analyzed and exhibited that Fe³⁺ owned obvious fluorescence quenching effect on LBE, while other metal ions possessed little or weak effect. Furthermore, the limit of detection (LOD) of Fe³⁺ was evaluated as 0.17 μM.

A facile synthesis of multifunctional carbon dots as fluorescence 'turn on' and 'turn off' probes for selective detection of Al3+ and 2,4,6-trinitrophenol

Carbon dots (CDs) have drawn increasing interests due to their unique optical properties and promising application in various fields. In this study, citric acid (CA) and 5-chloromethyl-8-hydroxyquinoline (LQ) were used to synthesize nitrogen-doped CDs as novel fluorescent probes using a one-step solvothermal route. The as-prepared CDs had strong blue-white fluorescence emission when excited at 405 nm wavelength with a quantum yield (QY) of 25%, behaving with high ion concentration stability. Water-soluble CDs with a 8-hydroxyquinoline structure on their surface could be used to detect Al³⁺ using a 'turn on' mechanism and trinitrophenol (TNP) using a 'turn off' mechanism with detection limits of 229 nM and 44.4 nM, respectively. Al³⁺ enhances the fluorescence of CDs by forming a coordination complex to generate a fluorescence synergistic role and limit CD nonradiative transition. TNP quenched the fluorescence with high selectivity and sensitivity, which was attributed to the inner filter effect and static quenching. These results indicated that these CDs with their unique 'turn on' and 'turn off' nature have potential application in the environmental protection field and in prevention of terrorist threats.

Facile Preparation of Stable Solid-State Carbon Quantum Dots with Multi-Peak Emission

Aggregation-caused quenching (ACQ) effect, known as the main cause to restrain solid-state luminescence of carbon quantum dots (CQDs), hinders further application of CQDs in white light-emitting diodes (WLED). Here, a complex of CQDs and phthalimide crystals (CQDs/PC) was prepared through a one-step solvothermal method. CQDs/PC prevented CQDs from touching directly by embedding the CQDs in phthalimide crystal matrix in situ, which effectively reduced the ACQ effect. Furthermore, CQDs/PC exhibited multi-peak fluorescence spectra that span the green, yellow and orange spectral regions. Finally, a WLED fabricated based on CQDs/PC achieved a color-rendering index of 82 and a correlated color temperature of 5430 K. This work provides a quick and effective strategy to apply CQDs to WLED.

Interparticle distance as a key factor for controlling the dual-emission properties of carbon dots

Due to their distinct and useful features, multi-color-emissive carbon dots (CDs) have gained much attention, however, their lack of red emission has so far limited their practical use for various applications, thus understanding of their emission origins is required. Concentration-dependent photoluminescence (PL) is a unique feature of CDs and is regarded as one way to realize tunable PL, providing information on their PL mechanism. In this work, we synthesized concentration-dependent blue/red dual-color-emissive CDs under single excitation at 365 nm. With the increase in concentration, the blue emission band showed a large red-shift from 431 to 500 nm, while the red emission band at around 650 nm showed only a relative intensity change, without a significant spectral shift. We performed spectroscopic analysis by changing the solution environment including the solvent type and pH to investigate the origins of the two emission bands. These results, combined with the zeta potential and fluorescence microscopy results, confirmed that the interparticle distance of CDs is a key factor for their dual-emissive PL behavior. With the advantage of unique PL features, we showed the potential of the CDs for white light-emitting diode (WLED) and ratiometric pH sensing applications.

Synthesis, applications and potential photoluminescence mechanism of spectrally tunable carbon dots

Due to the prominent characteristics of carbon-based luminescent nanostructures (known colloquially as carbon dots), such as inexpensive precursors, excellent hydrophilicity, low toxicity, and intrinsic fluorescence, these nanomaterials are regarded as potential candidates to replace traditional quantum dots in some applications. As such, research in the field of carbon dots has been increasing in recent years. In this mini-review, we summarize recent progress in studies of multicolor carbon dots focusing on potential photoluminescence (PL) mechanisms, strategies for effective syntheses, and applications in ion/molecule and temperature sensing, light emitting diodes and high-resolution bioimaging techniques.

Optimization and performance of nitrogen-doped carbon dots as a color conversion layer for white-LED applications

In this study, green-emitting nitrogen-doped carbon dots (N-CDots) were synthesized and incorporated into drop-cast composite films for use as color conversion layers in a white-LED configuration to generate white light. In order to resolve the red deficiency of this configuration, a commercial red phosphor was integrated into the system. Moreover, the N-CDots were also processed into polymer/N-CDot composite fibers, for which we determined the amount of N-CDots that yielded adequate white-light properties. Finally, we showed that white light with excellent properties could be generated by employing both of the fabricated N-CDot composites either as drop-cast films or composite fibers. Hence, N-CDots provide a promising alternative to inorganic phosphors that are commonly employed in white-LED configurations.

Full spectrum core-shell phosphors under ultraviolet excitation

A YAG

Ce/MgY4Si3O13:Ce-Y2O3:Eu core-shell structure was designed and accomplished via a urea homogeneous precipitation method. The as prepared phosphors can emit photons with a broad range of wavelengths from 340 nm to 700 nm under excitation light of 330 nm. The internal quantum efficiency can reach up to 68%.

Tailoring the Photoluminescence Excitation Dependence of the Carbon Dots via an Alkali Treatment

Carbon dots (CDs) have shown great potential in various applications including biomedicines and optoelectronics. However, the origin of their photoluminescence excitation dependence (PL-ED) still remains uncertain, and this can limit the full exploit of their wonderful optical properties. Here we studied the mechanism for the PL-ED of solvothermally synthesized CDs using an alkali treatment. As-synthesized CDs were found to agglomerate and exhibited multicolor emissions with strong PL-ED. The alkali treatment can effectively break down the clusters into individual CDs via the hydrolysis of the amide and ester bonds that link the CDs together. This process effectively narrowed the emission line width and suppressed the observed PL-ED. The understanding of the excitation dependence mechanism here outlined a novel strategy for tailoring of the PL-ED of CDs via a synergy of chemical and physical processes, thus enhancing the versatility of CDs for a broader spectrum of applications.

Polymer-Assisted Self-Assembly of Multicolor Carbon Dots as Solid-State Phosphors for Fabrication of Warm, High-Quality, and Temperature-Responsive White-Light-Emitting Devices

White-light-emitting devices (WLEDs) are considered to be a promising illumination source; especially, the WLEDs based on carbon dots (CDs) with white fluorescence have attracted extensive research interest. Herein, we report the design and implementation of solid white-light-emitting phosphors (WCDs@PS), which combine blue and orange emissive CDs (BCDs and OCDs) assisted by polystyrene (PS) through a self-assembly technique. Based on these phosphors (OCDs/BCDs = 1.2:1), the obtained WLEDs display a warm white light with International Commission on Illumination (CIE) coordinates of (0.35, 0.36), a high color rendering index of 93.2, a low correlated color temperature of 4075 K, and a luminous efficiency of up to 14.8 lm·W^-1. Interestingly, these WLEDs exhibit temperature-dependent emission performance, whose light-emission spectrum can be adjusted in situ from white (λ ∼ 400-730 nm) to blue (λ ∼ 440 nm) in the range of 20-80 °C. A change in CIE coordinates from (0.35, 0.36) to (0.32, 0.23) was also observed. The temperature-driven tunable LEDs as a thermochromism device could broaden the application of CDs-based lighting systems in special displays.

Ultraviolet-pumped white light emissive carbon dot based phosphors for light-emitting devices and visible light communication

Herein, we report UV-pumped white light emissive carbon dot (CD)-based phosphors to prevent blue light hazard in phosphor-converted WLEDs. Then, UV-pumped WLEDs with a color rendering index exceeding 85 and VLC with a modulation bandwidth of 75 MHz and a data transmission rate of 224 Mbps have been realized.

Yellow fluorescent graphene quantum dots as a phosphor for white tunable light-emitting diodes

Tunable color temperature of graphene quantum dot-based white lighting emitting diodes had been achieved adjusting the thickness and concentration of color convert matrix.

Investigation of local structure distortion and electron cloud interaction on emission-band broadening induced by the concentration perturbation effect of cation substitution in BaY2Si3O10:Eu phosphors

Here, we conceived a concentration perturbation effect to obtain cyan-emitting phosphors based on local structure distortion and electron cloud interaction.