Carbon Dots Powder Research Articles

Antibacterial and enhanced stability of carbon dot based on L-arginine modified by HPMC

Carbon dots tend to aggregate into clusters during lyophilisation, and the obtained powder is highly hygroscopic and not easy to store. This study introduces a simple way to solve it. Hydroxypropyl methyl cellulose(HPMC)was selected to enhance the stability of carbon dot powder after freeze-dried. Firstly, an interesting carbon dot had been prepared from L-arginine via hydrothermal method, which showed certain antibacterial properties towards E. coli and S.aureus. Secondly, mixing carbon dots aqueous solution with HPMC according to mass ration and stirred evenly. Put the mixture into freeze drying oven until dried, and got the powder, which was tested by XPS and IR. The results demonstrated that the content of surface element in carbon dots powder has changed and owned the characteristics of HPMC. The developed carbon dot powder exhibited similar antibacterial and optical properties to those solutions and emitted significant blue fluorescence when irradiated by an ultraviolet lamp. Importantly, the solid carbon dot powder has high stability under ambient temperatures. It is stable in storage for up to one year and is no longer hygroscopic. However, the common carbon dot aqueous solution without HPMC after freeze-drying is extremely hygroscopic at room temperature and not easy to store.

Novel solution and solid-state emissive long-wavelength carbon dots for water sensing and white LED applications

Carbon dots (CDs) are among the most popular nanomaterials due to their remarkable fluorescent and electronic properties, as well as their good biocompatibility and low cytotoxicity. Currently, CDs with aggregation-induced emission (AIE) are relatively rare and have become a significant research hotspot. This is because most conventional CDs suffer from severe quenching in a solid state. Herein, novel CDs with both solution and solid-state emissions were obtained using a facile one-step hydrothermal synthesis. Specifically, the CDs exhibit yellow solvent-dependent fluorescence in solution state (λem = 580 nm) and red AIE emission in solid state (λem = 640 nm). CDs powder is utilized as a red phosphor for light-emitting diode (LED). The resulting fabricated white LEDs (WLEDs) demonstrate good performance metrics, including a Color Rendering Index (CRI) of 89.5, Correlated Color Temperature (CCT) of 3876 K, and commission Internationale d’Éclairage (CIE) coordinates of (0.350, 0.331). Furthermore, the solvent-dependent phenomenon observed in AIE-CDs can be exploited to apply their solution as a highly sensitive fluorescence sensor for quantitatively detecting amounts of water in various organic solvents. The method offers both high accuracy and sensitivity, with R2 values varying from 0.853 to 0.994 and a low detection limit ranging from 0.296 to 3.23 % across a wide linear range. This inherent versatility makes the CDs suitable for a wide range of applications, including sensing and LED devices.

Large-Scale Synthesis of Tunable Fluorescent Carbon Dots Powder for Light-Emitting Diodes and Fingerprint Identification.

The emergence and fast development of carbon dots (CDs) provide an unprecedented opportunity for applications in the field of photoelectricity, but their practicability still suffers from complicated synthesis procedures and the substrate dependence of solid-state fluorescence. In this study, we design a unique microwave-assisted solid-phase synthesis route for preparing tunable fluorescent CD powders with yellow, orange, and red fluorescence (Y-CDs, O-CDs, R-CDs) by simply adjusting the mass ratio of reactants, a method which is suitable for the large-scale synthesis of CDs. The Y-/O-/R-CDs were systematically characterized using physics and spectroscopy techniques. Based on the perfect solid-state fluorescence performance of the proposed fluorescent CD powders, the Y-/O-/R-CDs were successfully applied for the construction of multi-color and white light-emitting diode devices at low cost. Furthermore, the Y-CDs displayed much higher yield and luminous efficiency than the O-CDs and R-CDs and were further used for fingerprint identification on the surfaces of glass sheets and tinfoil. In addition, the R-CD aqueous solution fluorescence is sensitive to pH, suggesting its use as a pH indicator for monitoring intracellular pH fluctuations. The proposed series of fluorescent powders composed of CDs may herald a new era in the application of optical components and criminal investigation fields.

Facile Microwave Synthesis of Efficient Green Emissive Carbon Dots Powder and Their Application in Visible Light Communication and White Light Emitting Devices

AbstractHighly green emissive solid‐state carbon dots (CDs) with photoluminescence quantum efficiency of 58% are prepared through a rapid microwave assisted heating method. Due to the spatial confinement from the biuret crystal matrix, aggregation among CDs is effectively suppressed, thus allowing the CDs to give efficient emission in the solid‐state. The CDs show excitation independent emission and mono‐exponential decay characteristics with a nearly constant lifetime of ≈13 ns upon varying the detected emissions, indicating the presence of a single type of emissive state in the CDs. Due to their high quantum efficiency and short lifetime, the obtained CDs are applied as the color conversion layer of a near‐ultraviolet micro light‐emitting diode (µLED) chip (405 nm) for visible light communication, achieving a modulation bandwidth of 165 MHz, which is much higher than the bandwidth of the conventional combination of Ce3+‐doped yttrium aluminum garnet phosphor with GaN LED. Moreover, the green emitting solid‐state CDs are applied to fabricate a prototype white LED device, which exhibits good lighting suitability with a color rendering index of 90.6 and a Commission Internationale de L'Eclairage chromaticity coordinates of (0.327, 0.332).

Aggregation-induced emission solid-state multicolor fluorescent carbon dots for LEDs and fingerprints applications

At present, most of the reported carbon dots (CDs) are still dispersed in the solvent in liquid state. However, solid-state CDs cannot fundamentally prevent the aggregation-caused quenching effect (ACQ), which seriously affects their application. Herein, hydrophobic solid-state luminescent CDs with typical aggregation-induced emission (AIE) behavior were synthesized by simple solvothermal method using dithiosalicylic acid (DSTA) and acetic acid. The AIE behavior of CDs is mainly due to the presence of disulfide bonds, which restrict the intramolecular rotation of CDs surface groups around them, thus generating solid-state fluorescence (SSF) in long-wave emission. In addition, by using MA, urea and sulfonamide to tune the emission behavior of CDs, red, yellow and green AIE CDs named R-CDs, Y-CDs and G-CDs were obtained successfully. The as-prepared CDs powder was further applied to fabricate multi-color light-emitting diodes (LEDs) on UV chips. The fabricated tri-color LED devices can maintain high color purity and color rendering index (CRI). More importantly, the Correlated color temperature (CCT) of the three LED devices was located in the warm light area, which could effectively reduce visual fatigue. Finally, we applied three kinds of AIE CDs in fingerprint detection and effectively displayed the details.

Anhydride-Terminated Solid-State Carbon Dots with Bright Orange Emission Induced by Weak Excitonic Electronic Coupling.

In this work, fluorescent solid carbon dots (CDs) welcome a new member, namely anhydride-terminated CDs, which have a photoluminescence quantum yield (PLQY) of 28% for orange-emitted CDs at 580 nm in powder form. For the first time, we revealed that the electronic coupling of the functional groups should be a crucial factor affecting the optical properties of solid CDs. Due to the negligible hydrogen bonding interaction between the anhydride groups, the electronic coupling of excitons between neighboring anhydride groups is weak, leading to a high PLQY of 28% and an immobile emission peak at 580 nm in solid state. Anhydride-terminated CDs can be partly converted into carboxyl-terminated CDs after dispersion in ethanol. However, the strong electronic coupling of carboxyl groups at high concentration generates the stacking mode of J-aggregates, giving rise to a red-shifted emission from 450 to 515 nm as well as quenched fluorescence in solid state. In comparison, a useful blue emission for solid-state CDs occurs from low sp2 hybridized carbon atoms, which possess weak electronic coupling and a stationary emission band at 450 nm in both solution and solid state. By adjusting the feed ratio of the reactants, the relevant intensities between the emission from low sp2 hybridized carbon atoms at 450 nm and the emission from anhydride groups at 580 nm can be controlled. As a result, single-component anhydride-terminated CD powder with tunable emission color from orange to white light can be achieved. As-prepared anhydride-terminated CDs can be used for fabricating light-emitting diodes (LEDs), white LEDs, and luminescent solar concentrators (LSCs).

Large scale synthesis of red emissive carbon dots powder by solid state reaction for fingerprint identification

Red emissive carbon dots (CDs) powder was synthesized on a large scale from phloroglucinol and boric acid by a novel solid state reaction with yield up to 75%. This method is safe and convenient, for it needs neither high pressure reactors nor complicated post-treatment procedures. The as-prepared carbon dots powder exhibited strong red fluorescence with excitation-independent behavior. XPS measurement and PL spectra suggest that such red fluorescence arise from boron-doped structures in CDs, which increases along with the boron concentration on CDs surface but decreases when the concentration quenching effect takes place. To overcome the aggregation induced fluorescence quenching of the solid CDs powder, the conventional methods are dispersing CDs into a large amount of inert substrates. But our present work provides a new strategy to realize strong red fluorescence of CDs in solid state. As a result, such carbon dots powder works well for latent fingerprint identification on various material surfaces.

Novel yellow solid-state fluorescent-emitting carbon dots with high quantum yield for white light-emitting diodes

Fluorescence quenching of carbon dots (CDs) occurs in their aggregated state ascribed to direct π–π interactions or excessive resonance energy transfer (RET). Thus, CDs have been severely restricted for applications requiring phosphors that emit in the solid state, such as the fabrication of white light-emitting diodes (WLEDs). In this report, novel CDs with bright solid-state fluorescence (SSF) were synthesized by simple microwave-assisted synthesis method, using 1,4,7,10-tetraazacyclododecane (cyclen) and citric acid as precursors. Under 365 nm UV light, these CDs emit bright yellow SSF, indicating they successfully overcome the aggregation-induced fluorescence quenching (ACQ) effect. When the excitation wavelength (λex) is fixed at 450 nm, the emission peak of the CDs is centered at 546 nm with the Commission Internationale de l’Eclairage chromaticity (CIE) coordinates of (0.43, 0.55), which means that they can be combined with a blue-emitting chip in order to fabricate WLEDs. More importantly, the absolute quantum yield (QY) of these CDs powder reached 48% at λex of 450 nm, which was much higher than many previously reported SSF-emitting CDs and indicating their high light conversion ability in solid-state. Thanks to the excellent optical property of these CDs powder, they were successfully used in the preparation of high-performance WLEDs. This study not only enriches SSF-emitting CD-based nanomaterials with good prospects for application, but also provides valuable reference for subsequent research on the synthesis of solid-state fluorescent CDs.

One step synthesis of hydrophobic carbon dots powder with solid state emission and application in rapid visualization of latent fingerprints

A one step thermal carbonization method for the preparation of solid state emitting N-doped carbon dots (NCDs) powder with hydrophobic nature is reported here. This method directly offers glowing NCDs powder in large quantities and do not involve tedious purification and drying steps. Physicochemical properties of as produced NCDs were explored using various analytical techniques and optical properties were studied in different solvents. The NCDs powder was applied for the rapid visualization of latent fingerprints (LFPs) on various porous and non-porous surfaces. With their green emission, NCDs were able to provide sufficient contrast on auto-fluorescent surfaces also. The LFPs developed with NCDs powder clearly presented level 2 and level 3 ridge details which are sufficient for the individual identification. • One step synthesis of N-doped carbon dots powder (NCDs) with solid state emission. • NCDs can be obtained in large quantities without tedious purification and drying. • NCDs exhibited hydrophobic and organophilic nature. • Detection of latent fingerprints by NCDs powder with stable bluish green emission. • Level 2 and level 3 ridge details and good contrast on auto-fluorescent surface.

Dispersing carbon dots in non-polar rubber by slurry compounding and in situ compatibilizing

Carbon dots (CDs) have gained increasing attention in the elastomer composites due to their unique physical and chemical properties. Nevertheless, due to high hydrophilicity of most kinds of CDs, it is difficult to achieve a fine CDs dispersion within the non-polar rubbers by traditional melt milling, especially when the CDs loading is high. To tackle this problem, we propose a simple and cost-effective strategy, i.e., the combination of slurry compounding and in-situ compatibilizing, to prepare the rubber/CDs composites. The CDs slurry was simply prepared by mixing the CDs powder with water. Subsequently, the slurry along with the compatibilizer (polybutadiene grafted with maleic anhydride, BR-g-MAH) were compounded with rubber via open milling. The resulted rubber composites exhibited significantly improved mechanical properties. More importantly, the CDs endowed the rubber with exceptional antioxidative property. We envisage that this scalable yet environmentally-friendly strategy may pave the way for industrial-scale utilization of CDs in the elastomer and beyond.

Photo-Stimulated Polychromatic Room Temperature Phosphorescence of Carbon Dots.

Single-component multicolor luminescence, particularly phosphorescence materials are highly attractive both in numerous applications and in-depth understanding the light-emission processes, but formidable challenges still exist for preparing such materials. Herein, a very facile approach is reported to synthesize carbon dots (CDs) (named MP-CDs) that exhibit multicolor fluorescence (FL), and more remarkably, multicolor long-lived room temperature phosphorescence (RTP) under ambient conditions. The FL and RTP colors of the CDs powder are observed to change from blue to green and cyan to yellow, respectively, with the excitation wavelength shifting from 254 to 420 nm. Further studies demonstrate that the multicolor emissions can be attributed to the existence of multiple emitting centers in the CDs and the relatively higher reaction temperature plays a critical role for achieving RTP. Given the unique optical properties, a preliminary application of MP-CDs in advanced anti-counterfeiting is presented. This study not only proposes a strategy to prepare photo-stimulated multicolor RTP materials, but also reveals great potentials of CDs in exploiting novel optical materials with unique properties.

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

Plastic waste is generally resistant to natural degradation and has become a major environmental pollution problem globally. The pollution of ecosystems seriously affects the health and survival of organisms, including humans. Much attention has been paid to finding suitable ways to convert plastic waste into high-value-added carbon materials. To this end, we report the high production yield (60%–85%) of carbon dots (CDs) for solid-state fluorescence (SSF) obtained by a one-step solvothermal method using waste expanded polystyrene as the precursor. The SSF mechanism of the CDs was also explored. Their emission wavelength, with a large full width at half maximum of 150–200 nm, exhibited tunable photoluminescence from white to yellow and orange. CDs powder was used to fabricate single-component white and multi-colour light-emitting diodes on UV chips. Overall, plastic waste was converted into tunable solid-state fluorescent CDs powder, which has promising applications in carbon-based lighting, by a simple solvothermal method that provides a viable method for recycling plastic waste.

Facile microwave synthesis of carbon dots powder with enhanced solid-state fluorescence and its applications in rapid fingerprints detection and white-light-emitting diodes

In this report, we successfully developed a simple and fast MW-assisted method for preparing CDs with strong solid-state fluorescence (SSF) by using phthalic acid and piperazine as precursors. The prepared p-CDs can be obtained in high yield (48.7%) and emit bright yellow-green SSF under 365 nm UV light. The absolute PL quantum yield (PLQY) of p-CDs in solid state was measured to be 20.5%, which is much higher than that in aqueous solution. This interesting phenomenon shows that p-CDs not only successfully conquer the aggregation-caused fluorescence quenching (ACQ) effect, but also achieve enhanced fluorescence emission, which was rarely reported in previous literatures as CDs in solid state always reduce their fluorescence emission due to the excessive resonance energy transfer (RET) or direct π-π interactions. In addition, the relationship between the feed ratio of precursors and optical properties of the CDs were also investigated detailedly. Based on their strong SSF, the p-CDs were successfully used in rapid latent fingerprints detection and white light-emitting diodes (WLEDs) preparation with high quality. In summary, this research not only developed a new type of CDs with strong enhanced SSF, but also offered a valuable reference for design SSF-emitting CDs with high yield.

Diamond-like carbon structure-doped carbon dots: A new class of self-quenching-resistant solid-state fluorescence materials toward light-emitting diodes

The construction of simple and low-cost light-emitting diode (LED) based on carbon dots (CDs) powder is an important and challenging task. Here, diamond-like carbon (sp3C) structure-doped carbon dots (D-CDs) powder was prepared within 8 min via a one-step microwave-assisted pyrolysis route with a high production yield of 67.8%. The obtained D-CDs powder emits bright solid-state fluorescence without any other additional solid matrices and exhibits a quantum yield of 67.7%. Self-quenching effect caused by direct π-π interactions and fluorescence resonance energy transfer is strongly suppressed by the sp3 and sp2 carbon hybrid structure and the single energy level in the D-CDs powder. The D-CDs powder was directly employed as phosphors in LED, and bright blue LED was successfully constructed with maximum luminance achieving 3922 cd m−2. More importantly, the introduction of diamond-like carbon (sp3C) structure opens a new era for the preparation of CDs powder with solid-state fluorescence.

A facile hydrothermal method for preparation of fluorescent carbon dots on application of Fe3+ and fingerprint detection

The carbon dots (CDs) was prepared by a facile hydrothermal treatment of citric acid and glycine at 180 °C. The CDs at around 3.2 nm was collected after filtration and dialysis. The sample displayed green fluorescence (G-CDs) with a quantum yield of 3.7% in high concentration and the strongest emission peak was at 545 nm under the excitation wavelength of 480 nm; the blue fluorescence CDs (B-CDs) with a quantum yield of 29.8% was obtained after diluted either in solution or in powder, the strongest emission peak was located at 475 nm under the excitation wavelength of 380 nm. The G-CDs possessed a high selectivity to Fe3+, which was in a linear range of 0–3.5 μM with the detection limit of 0.21 μM. The CDs powder with blue fluorescence at a relative low content was obtained and adaptable for the fingerprint detection on substrates of litmus paper, resin tabletop, glass, and orange plastic ruler.

A self-quenching-resistant carbon dots powder with tunable solid-state fluorescence and their applications in light-emitting diodes and fingerprints detection

In this report, a novel type of carbon dots (CDs) were prepared via a simple MW-assisted method by using citric acid and piperazine as precursors. The CDs can be obtained in large-scale and emit bright solid-state fluorescence (SSF) with different colors. Then the synthetic CDs were fully characterized with PL, UV, XPS, TEM, and FTIR and the relationship between the mass ratio of precursors and physicochemical property of the CDs was also investigated detailedly. The results showed that these CDs prepared at different mass ratios have different element content and functional group content. More importantly, the mass ratio of the precursors not only has a great influence on their particle sizes, but also can affect their PL properties. With the decreased of the mass ratio, their particle size decreased gradually and their emission wavelength gradually red-shift. This interesting finding may be helpful for fabricating CDs with controllable particle size and tunable light-emitting colors. Based on their excellent SSF property, these CDs were successfully used to fabricate light-emitting diodes (LEDs) and detect latent fingerprints (LFPs). In conclusion, the research may offer a valuable reference for obtaining CDs with SSF and developing LEDs phosphors and LFPs detection reagent.