Red Carbon Dots Research Articles

Multicolor Carbon Dots Prepared by Single‐Factor Control of Graphitization and Surface Oxidation for High‐Quality White Light‐Emitting Diodes

AbstractIn a reaction system of asparagine and p‐phenylenediamine, blue, green, orange, and red carbon dots (CDs) are successfully prepared by adjusting the ratio of the two reactants. The obtained multicolor CDs have excellent stable properties and high fluorescence quantum yields (up to 74%). Clarifying the luminescence mechanism of multicolor CDs is based on the investigation of the composition, structure, and fluorescence properties of the CDs combined with quantum chemistry calculations. A high‐quality white light‐emitting diode (LED) with CIE color coordinates (0.33, 0.33) is successfully fabricated using a multicolor CD‐epoxy resin composite, and its color temperature and color rendering index are 5612 K and 94, respectively. It is of great significance to prepare multicolor CDs with high fluorescence quantum yields by single‐factor control. Using multicolor CDs to fabricate standard white LEDs close to sunlight will significantly increase the practical application value of CDs.

Revealing graphitic nitrogen participating in p–π conjugated domain as emissive center of red carbon dots and applied to red room-temperature phosphorescence

The fluorescence center of R-CDs is derived from the p–π conjugation effect of graphitic nitrogen, which can promote effective red RTP emission.

Field-portable ratiometric fluorescence imaging of dual-color label-free carbon dots for uranyl ions detection with cellphone-based optical platform

Under the public spotlight, uranyl (UO22+) ions has attracted considerable attention for the extreme radioactive and chemical toxicity to ourselves and our environment. Herein, we present a simple and effective ratiometric fluorescence imaging method for the visualizing and quantitative detection UO22+ ions by cellphone-based optical platform. The sensing solution was prepared by mixing label-free red carbon dots (r-CDs) and blue carbon dots (b-CDs) together with a fixed photoluminescence intensity ratio of 4:1. When UO22+ ions were added, the fluorescence of r-CDs can be selectively quenched, while the fluorescence of b-CDs remains stable without spectral changes. With the gradually increase the amounts of UO22+ ions, the different response of dual-color CDs resulted in a signification color evolution from deep red to dark purple under the ultraviolet (UV) light illumination. Then, a cellphone-based optical platform was constructed for directly imaging the color change of the samples, and the built-in Colorpicker APP quickly output the red, green and blue (RGB) channel values of these images within one second. Interesting, there was a linear relationship between the ratio of red and blue (R/B) channel values and UO22+ ions concentration from 0 μmol/L to 30.0 μmol/L (R2 = 0.92804) with the detection limit of ∼8.15 μmol/L (signal-to-noise ratio of 3). In addition, the optical platform has also been applied to the quantification of UO22+ ions in tap water and river water sample. With the advantage of low-cost, portable, easy to operation, we anticipate that this method would greatly improve the accessibility of UO22+ ions detection even in resource-limited areas.

Visual monitoring of trace water in organic solvents based on ecofriendly b/r-CDs ratiometric fluorescence test paper

Developing a green, non-toxic and easy to synthesize of fluorescence probe for fast and visual detecting trace water in various organic solvents was an important task. Here, a novel dual-emission fluorescence probe (b/r-CDs) was designed based on the red CDs (r-CDs) and blue CDs (b-CDs) to detect the trace water and enhance the visualization for naked-eye observation in different organic solvents. Among, the red fluorescence carbon dots (CDs) was found to have the capability to monitor trace amounts of water, which synthesized with green tea by facile ultrasonic method. Further, Such a dual-emission probe could fast monitor trace water in various organic solvents with high stability and fast response. Importantly, a synergistic mechanism of the dynamic process (b-CDs) and static quenching (r-CDs) was proved for the study of water detection. Moreover, the test paper was made for detecting trace water in different organic solvents, achieving convenient and effective detection.

A facile microwave-assisted synthesis of highly crystalline red carbon dots by adjusting the reaction solvent for white light-emitting diodes

Microwave approach has been widely used for the synthesis of fluorescent carbon dots (CDs) due to its advantages of short reaction time and homogeneous heating. Currently, it is still difficult to synthesize red light-emitting CDs (R-CDs) via the microwave-assisted method at atmospheric pressure. Herein, we report a solvent-controlled synthesis of R-CDs using domestic microwave. As a result, for an ammonium citrate tribasic, formamide and glycerol blend reaction solvent, the R-CDs with emission peak of 622 nm were achieved and exhibited a photoluminescence (PL) quantum yield of 37.4% and excitation-independent PL emission spectrum. During the formation process of R-CDs, glycerol and formamide not only promote the carbonization of ammonium citrate tribasic, but can also enhance the crystalline nature of CDs. Finally, the warm white light-emitting diode (WLED) with a high colour rendering index (CRI) of 90.9 and Commission Internationale de L’Eclairage (CIE) coordinates of (0.344, 0.333) was realized by combining conventional yellow YAG:Ce phosphor and R-CDs/mesoporous silica (MPS) composites with a blue chip. This result demonstrates a low-cost R-CD synthetic method for potential substitution for red phosphor materials in solid-state lighting applications.

Multifunctional red carbon dots: a theranostic platform for magnetic resonance imaging and fluorescence imaging-guided chemodynamic therapy.

In recent years, carbon dots (CDs) with red-emitting wavelengths have received increasing attention in cancer therapy and imaging. Here, we reported a multi-functional CD based platform combining bimodal magnetic resonance/fluorescence (MR/FL) imaging and chemodynamic therapy (CDT) for in vivo imaging of tumor tissues and efficient anticancer treatment. The red-emitting CDs were synthesized via a one-step solvothermal method with p-phenylenediamine as the carbon source. Ethylenediaminetetraacetic acid (EDTA) was covalently coupled to the surface of CDs and then complexed with Fe2+ and Gd3+ to obtain functionalized red CDs (CDs@EDTA@Gd@Fe). CDs@EDTA@Gd@Fe exhibited bright and stable fluorescence and strong T1-weighted MR imaging (MRI) contrast. Moreover, the CDs@EDTA@Gd@Fe showed an excellent anticancer effect both in vitro and in vivo via a Fenton reaction-based CDT by releasing Fe2+ in the tumor. Our study offers a promising strategy for developing multi-functional CDs for cancer theranostics.

Evaluation of Commercial “Carbon Quantum Dots” Sample on Origins of Red Absorption and Emission Features

The commercially acquired aqueous solution of “carbon quantum dots” sample was evaluated by optical absorption and fluorescence emission methods; in reference to aqueous dispersed small carbon nanoparticles and representative carbon dots prepared from chemical functionalization of the carbon nanoparticles. The results suggest a very low content of carbon that is associated with nanoscale carbon particles/domains in the as-supplied sample; and likely significant contamination by dye-like species/mixtures. In the absence of any information on the synthesis and history of the commercial sample, the possible cause of the contamination was illustrated by an example on similar dye formation in the one-pot carbonization synthesis of “red carbon dots” from citric acid–formamide precursor mixtures under too mild processing conditions that were insufficient for the intended carbonization. The negative impacts to the carbon dots research field by the apparent proliferation and now commercial availability of carbon-deficient or even largely carbon-less “carbon quantum dots”, which are more susceptible to dye contamination or dominance, are discussed.

Red carbon dots as label-free two-photon fluorescent nanoprobes for imaging of formaldehyde in living cells and zebrafishes

Direct, in situ selective detection of intracellular formaldehyde (FA) is of great significance for understanding its function in FA-related diseases. Herein, red carbon dots (RCD) are reported as label-free two-photon fluorescent nanoprobes for detecting and imaging of FA. Upon addition of FA, the -NH2 groups of RCD could quickly and specially react with aldehydes to form Schiff base and then the strong fluorescence of RCD with blue-shift emission is recovery due to the destruction of the hydrogen bond interaction between RCD and water. In addition, the nanoprobes exhibit outstanding photostability, rapid response (<1 min), high sensitivity (∼9.9 μmol/L) and excellent selectivity toward FA over other aldehyde group compounds. Notably, owing to the good cell-membrane permeability and biocompatibility, as well as the large two-photon absorption cross-section, the as-prepared RCD can be used as label-free nanoprobes for selectively detecting and imaging FA in living cells and zebrafishes through one-photon and two-photon excitation. Moreover, RCD could stain the tissue of zebrafishes at depths interval of up to 240 μm under two-photon excitation. This research implied that RCD are promising tools for directly and in situ imaging FA in vivo, thus providing critical insights into FA-related pathophysiological processes.

Synthesis of high-efficient red carbon dots for pH detection

A facile one-step solvothermal route for the preparation of high-efficient red fluorescence carbon dots (RCDs) is developed using 2-aminophenol as carbon source. The as-prepared RCDs indicate excitation-independent emission at 615 nm, high absolute photoluminescence (PL) quantum yield (24%) in ethanol, excellent water solubility, high optical stability and sensitive pH response behavior. The RCDs-based “off-on” reversible probe can be used to detect H+ and OH−. The quenching and recovering effects can be obviously observed by naked eyes due to the combination effect between the target ions and the surface functional groups of RCDs, resulting in breaking or recombination of the quenchers. Moreover, a remarkable fluorescence enhancement behavior with the increase of pH from 4 to 13 can be induced by the RCDs, which can be also used to detect H+ and OH− in urine of cattle and lake water, exhibiting a promising platform of the RCDs for environmental and biological sensing applications.

One Pot Generation of Blue and Red Carbon Dots in One Binary Solvent System for Dual Channel Detection of Cr3+ and Pb2+ Based on Ion Imprinted Fluorescence Polymers

Blue and red dual channel dual emission carbon dots (DDCDs) were synthesized by a one-step hydrothermal method in water-formamide binary system using citric acid and ethylenediamine as precursors. Then, the as-prepared DDCDs were directly employed for preparation of ion imprinted fluorescence polymers without further separation. Since Cr3+ can only quench the fluorescence of blue CDs, while Pb2+ only quenches the fluorescence of red CDs, dual channel detection of Cr3+ and Pb2+ can be achieved simultaneously based on ion imprinted fluorescence polymers. Under optimized conditions, the quenching effect [(F0 - F)/F0] at 440 nm for the blue channel against the concentration of Cr3+ was linear from 0.1 to 6.0 μM, while that for the red channel at 580 nm against the concentration of Pb2+ was linear from 0.1 to 5.0 μM. The detection limits for Cr3+ and Pb2+ can reach 27 nM and 34 nM, respectively. Satisfied recoveries have also been obtained for detection of Cr3+ and Pb2+ in real water samples. The application of this dual channel detection method will greatly simplify the heavy metal ion detection process in complicated water environments.

Semiquantitative Visual Detection of Lead Ions with a Smartphone via a Colorimetric Paper-Based Analytical Device.

A simple, instrument-free, paper-based analytical device with dual-emission carbon dots (CDs) (blue CDs and red CDs) was developed for the semiquantitative, visual, and sensitive speciation analysis of lead ions in a real sample with a sensitive detection limit of 2.89 nM. When a paper strip was immersed into the sample solution, the blue fluorescence was quenched by Pb2+ in solution, while the red fluorescence served as a background reference without color change, and significant color evolutions from blue to red were observed under the ultraviolet lamp, resulting in a semiquantitative visual detection. Furthermore, a smartphone was used in the visual detection of lead ions by identifying the RGB value of the fluorescent probe solution and corresponding paper strip. The application of smartphones and fluorescent paper strips has greatly shortened the detection time and reduced the cost of detection, providing a new strategy for the on-site and semiquantitative detection of heavy-metal ions in water samples.

Red carbon dots: Optical property regulations and applications

Recent years have witnessed a rapid development of the fluorescent carbon dots (CDs), due to their distinctive advantages of straightforward synthesis, excellent biocompatibility, low cost, and tunable optical properties. However, the widespread applications of CDs in biomedical theranostics, light harvesting, and photocatalysis are limited by the lack of emission and/or excitation in the red/near-infrared (NIR) region. Extensive explorations have been conducted to synthesize CDs with intensive red/NIR emission/excitation (red CDs) by rational design and ingenious synthesis to broaden their applications. This review emphasizes the most recent efforts in the development of CDs with intensive emission at a long wavelength, with a focus on the regulation methods for the optical properties of CDs, including particle size, surface state, and heteroatom doping. Key factors in processing red CDs, such as reaction solvent and precursors, are demonstrated. More importantly, employing polyaromatic and dye molecules as carbon sources is highlighted, which could further expand emission/excitation to the NIR region. The boosting applications of red CDs in white light-emitting diodes (WLEDs), biosensing, bioimaging, theranostics, and photocatalysis are demonstrated. Finally, the challenges and perspectives of red CDs are also discussed.

Multicolor tunable highly luminescent carbon dots for remote force measurement and white light emitting diodes.

Multicolor tunable carbon dots (CDs) are obtained by only altering the reaction solvents in solvothermal treatment. The red CDs (R-CDs) have a quantum yield of 50.8%, the highest reported for nitrogen and sulfur co-doped R-CDs so far. These CDs are developed into fluorescent hydrogels for precise remote force measurement and WLEDs with the CIE color coordinate of (0.31, 0.32).

Preparation of N-doped yellow carbon dots and N, P co-doped red carbon dots for bioimaging and photodynamic therapy of tumors

We report on the preparation of N, P co-doped red carbon dots and their applications in bioimaging and photodynamic therapy of tumors.

Highly fluorescent dual-emission red carbon dots and their applications in optoelectronic devices and water detection

Synthesis of dual-emission nitrogen and sulfur co-doped (N,S)-CDs with a quantum yield up to 29.7% and their applications in white LEDs and water detection.

Fingerprint identification of copper ions with absorption and emission dual-mode responses by N,S co-doped red carbon dots

Highly selective and sensitive Cu2+-based sensors have been successfully developed by N,S co-doped red emissive carbon dots with absorption and emission dual-mode recognition strategies.

Polyelectrolyte-protected Dual-color-quantum-dot Assembled Silica Nanoparticles and Their Application in Simultaneous Fluorescence Determination of e Antigen and Surface Antigen of Hepatitis B.

Cationic poly-diallyldimethylammonium (PDADMAC), green CdTe quantum dots (QDs) or red CdS coated CdTe QDs, and anionic polyacrylic acid (PAA) were respectively assembled on the nano-carrier SiO2 to prepare green fluorescence composite nanoparticles (GF-QDs) and red ones (RF-QDs) with the structure SiO2/PDADMAC/QD/PDADMAC/PAA. The sandwich structure "PDADMAC/QD/PDADMAC" on the nano-carrier not only realized the protection to fluorescence of QDs but also avoided the fluorescence shielding of silica shell for the assembled QDs. In 7 days, the diluent solutions of GF-QD and RF-QD all have a very stable fluorescence. On the contrary, the fluorescence of diluent solutions of red and green QDs reduced by 75.99 and 94.35%, respectively. Indeed, they have not fluorescent shielding and have a very slight fluorescent enhancement. Based on GF-QD and RF-QD, the simultaneous determination of Hepatitis B e antigen and surface antigen has been established. Their determination in buffer and plasma all showed good precision and accuracy.

Red C-dots and C-dot films: solvothermal synthesis, excitation-independent emission and solid-state-lighting

Currently, fluorescent carbon dots (CDs) have attracted great attention for their unique optical performance. However, the shortage of red emissive CDs and the corresponding CD solid samples with intense luminescence significantly limit their applications in optoelectronic fields. In the present work, red fluorescence CDs were successfully synthesized via a facile solvothermal reaction using p-phenylenediamine as the carbon source and isopropanol as the solvent. Excitation-independent luminescence and emission-independent decay indicated that one dominant type of emissive state was responsible for red luminescence, which was evidenced to be a N-related surface defect state with the help of structural and spectroscopic characterizations. Furthermore, CD-embedded PVA solid films, exhibiting bright red emission with intense absorption in the blue-light region, were prepared to explore their possible application as a color converter in solid-state lighting. As a proof-of-concept experiment, white light-emitting diode devices were constructed by combining a red CD solid film and yellow Ce:YAG phosphor-in-glass with a commercial InGaN blue chip, showing tunable color coordinates, color rendering index and correlated color temperature via modifying the thickness of the CD film.

Cavity-Enhanced Microphotoluminescence in a Core–Shell n–p CdS/CdO Micrometer Wire and Its Efficient Surface Photovoltage Responses in the Whole Visible Range

A one-step growth of yellow and red CdS:O wires has been realized by a SnO2-catalyzed chemical vapor deposition (CVD) technique. The yellow and red CdS:O wires were obtained upon the temperature rising rates in the tube furnace. Yellow nanowire with less oxygen doping shows luminescent behavior from the acceptor trapped excitons near the band edge of the CdS nanowire. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations proved their formation of the CdS/CdO core–shell red wire due to O segregations in the CdS lattice when the oxygen doping concentration was higher than 4%, even up to 20%. Their microluminescence profiles are mainly caused by the CdO shell in the red wire, which gives temporally localized exciton emissions near the CdO band edge (600 nm) by femtosecond-pulse excitation and red-shift enhanced whispering-gallery mode (WGM) cavity mode emissions by a 488 nm continuous wave (CW) laser excitation. The luminescence of the CdS/CdO wire reflects the electronic state modification for CdO nanowires with no luminescence due to the p–n junction formation. The photovoltaic (PV) spectra of yellow and red wire aggregates show CdS and CdS/CdO profiles, respectively. The CdS/CdO wires have an extended PV responses from 510 to 800 nm as compared with CdS, the photocarrier type in the 300–510 nm range likes n-CdS, while that in the 510–800 nm range is p-type from the CdO shell. Both luminescence and PV responses could be enhanced by the WGM mode and core–shell n–p junction within a wire with dual PV zones. Such wires can find potential applications in the solar cells and nanophotonic devices.

Visible detection of copper ions using a fluorescent probe based on red carbon dots and zirconium metal-organic frameworks.

A highly selective and sensitive ratiometric fluorescent probe for copper ions (Cu2+) in aqueous solution based on a blue zirconium metal-organic framework [UiO-66-(COOH)2] with red bandgap fluorescent carbon quantum dots (R-BF-CQDs) is developed. UiO-66-(COOH)2 displays broad ligand-centered (LC) emission and R-BF-CQDs shows red emission. Interestingly, the remaining -NH2 at the surface of the prepared R-BF-CQDs can coordinate Cu2+ efficiently and produce a strong visible absorption, which overlaps the emission of UiO-66-(COOH)2. There is also a strong coordination capacity of the Cu2+ ions with R-BF-CQDs and UiO-66-(COOH)2, which allows the energy donor and the energy receptor to be closer together. Both of these two conditions provide the possibility of spectral energy transfer. In practice, the LC emission of UiO-66-(COOH)2 becomes weaker with increasing concentration of Cu2+, whereas the red fluorescence of R-BF-CQDs increases slightly.