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

Recent advances in fluorescence and afterglow of CDs in matrices

Carbon dots (CDs) are novel nanomaterials with dimensions less than 10 nm that have attracted much attention due to their outstanding optical properties. However, the development of solid-state fluorescence and afterglow methods has been relatively slow, although the properties of these materials under liquid conditions have been extensively studied. In recent years, embedding CDs in a matrix has been shown to prevent aggregation quenching and inhibit nonradiative transitions, thus realizing solid-state fluorescence and afterglow, which has greatly broadened the research and application areas of CDs. In terms of hydrogen bonding, ionic bonding, covalent bonding and spatial confinement, the interactions between CDs and matrices can effectively realize and improve the solid-state fluorescence and afterglow effects of CDs. Recent applications of CDs in matrices in optoelectronics, information security, sensing, biotherapeutics and imaging are also summarized. Finally, we summarize the challenges and developments of CDs in matrices.

Investigation on broadband emission of two-dimensional melamine lead iodide perovskite (2D-C3H8N6PbI4): An experimental and theoretical approach

Novel two-dimensional melamine lead iodide perovskite (2D-C3H8N6PbI4) is synthesized to investigate its crystallinity, optical band gap and broadband emission properties and to make comparisons with 2D-C3H8N6PbCl4/2D-C3H8N6PbBr4 perovskites. Both experimental and density functional theory (DFT) interrogations on 2D-C3H8N6PbX4 (X = Cl, Br and I) are conducted. The crystal structure, morphology and percentile of Pb and halide elements are confirmed using scanning electron microscope (SEM), and energy dispersive spectrum (EDS), powder/single crystal X-ray diffraction (PXRD/SXRD), DFT and X-ray crystallography simulations. The optical band gaps of 2D-C3H8N6PbX4 perovskites are determined from the Tauc plot fitting of absorbance and DFT studies. Distinct broadband emission of 2D-C3H8N6PbX4 perovskites between 300 and 800 nm is observed, which can be fitted with multiple Gaussian distributions. The fittings of broad PL spectra from 2D-C3H8N6PbCl4/2D-C3H8N6PbBr4 perovskites confirm the involvement of both Dexter energy transfer from melamine cation and self-trapped excitons (STEs). However, the broadband emission of 2D-C3H8N6PbI4 is attributed only to the Dexter energy transfer from melamine cation and the absence of STEs is attributed to the larger lattice deformation of 2D-C3H8N6PbI4. Moreover, the involvement of spin-orbit coupling (SOC) in the energy transfer is clarified to attest that the broadband emission of 2D-C3H8N6PbI4 is distinct among its halide family.

One-pot synthesis of nitrogen-doped carbonized polymer dots with tunable emission for multicolor light-emitting diodes

Carbonized polymer dots (CPDs) have highly potential application value in the field of optoelectronic devices due to their preferable stability, excellent optical properties and low cost. Here, the nitrogen-doped carbonized polymer dots (HNCDs) with self-quenching-resistant fluorescence were prepared via a simple solvothermal method with citric acid, urea and 2-hydroxyethyl methacrylate (HEMA) as raw materials. The structure and optical properties of the HNCDs have been explored in detail by various contrast experiments. The results show that HEMA form the poly(HEMA) to modify on the surface of carbonized core, which can overcome the quenching effect of carbonized core. The nitrogen doping is crucial for the red shift emission of solid-state HNCDs. Furthermore, the HNCDs exhibit concentration-dependent emission and excellent compatibility with silicone sol, which lead to their emission red shifted from blue to red with increasing concentration. The HNCDs were further applied to construct the light-emitting diodes (LEDs), and the multicolor LEDs ranging from blue to red can be prepared by simply varying the type of chips and adjusting the concentration of HNCDs in encapsulating material.

Preparation of Berberine@carbon Dots Nano-Formulation: Synthesis, Characterization and Herbicidal Activity against Echinochloa crus-galli and Amaranthus retroflexus Two Common Species of Weed

Berberine (Ber) is easy to synthesize and has a variety of biological and pharmacological activities. At present, the existing studies on berberine have focused predominantly on its antibacterial activity; its herbicidal activity is rarely reported. In addition, there are a number of preparations of berberine, which are not enough to solve its shortcomings of low solubility and biological activity and the difficult storage of berberine. Here, berberine was combined with carbon dots to obtain carbon dots-berberine (CDs-Ber) nano formulation. The fluorescence quenching results showed that the CDs-Ber nano drug delivery system was successfully constructed, and the fluorescence quenching mechanism of the two was static quenching. The bioassay results showed that CDs had no adverse effects on the growth of barnyard grass (Echinochloa crus-galli) and redroot pigweed (Amaranthus retroflexus), and had high biocompatibility. Berberine and CDs-Ber predominantly affected the root growth of barnyard grass and redroot pigweed and could enhance the growth inhibition effect on weeds, to some extent. The results of the protective enzyme system showed that both berberine and CDs-Ber could increase the activities of Superoxide dismutase (SOD), Peroxidase (POD), and Catalase (CAT) in barnyard grass, and CDs-Ber had a stronger stress effect on barnyard grass than berberine. The determination of the number of bacterial communities in the soil after the berberine and CDs-Ber treatments showed that there was no significant difference in the effects of the two, indicating that CDs-Ber would not have more negative impacts on the environment. The CDs-Ber nano formulation improved the biological activity of berberine, enhanced the herbicidal effect, and was relatively safe for soil colonies.

Preparation of Nitrogen and Sulfur Co-Doped Fluorescent Carbon Dots from Cellulose Nanocrystals as a Sensor for the Detection of Rutin

The poor water solubility, large particle size, and low accessibility of cellulose, the most abundant bioresource, have restricted its generalization to carbon dots (CDs). Herein, nitrogen and sulfur co-doped fluorescent carbon dots (N, S-CDs) were hydrothermally synthesized using cellulose nanocrystals (CNC) as a carbon precursor, exhibiting a small particle size and excellent aqueous dispersion. Thiourea was selected as a nitrogen and sulfur dopant to introduce abundant fluorescent functional groups into N, S-CDs. The resulting N, S-CDs exhibited nanoscale size (6.2 nm), abundant functional groups, bright blue fluorescence, high quantum yield (QY = 27.4%), and high overall yield (16.2%). The excellent optical properties of N, S-CDs endowed it to potentially display a highly sensitive fluorescence "turn off" response to rutin. The fluorescence response for rutin allowed a wide linear range of 0-40 mg·L^-1, with a limit of detection (LOD) of 0.02 μM, which revealed the potential of N, S-CDs as a rapid and simple sensing platform for rutin detection. In addition, the sustainable and large-scale production of the N, S-CDs in this study paves the way for the successful high-value utilization of cellulose.

Multicolor Nitrogen-Doped Carbon Quantum Dots for Environment-Dependent Emission Tuning

Carbon quantum dots (CQDs) have potential applications in many fields such as light-emitting devices, photocatalysis, and bioimaging due to their unique photoluminescence (PL) properties and environmental benignness. Here, we report the synthesis of nitrogen-doped carbon quantum dots (NCQDs) from citric acid and m-phenylenediamine using a one-pot hydrothermal approach. The environment-dependent emission changes of NCQDs were extensively investigated in various solvents, in the solid state, and in physically assembled PMMA-PnBA-PMMA copolymer gels in 2-ethyl-hexanol. NCQDs display bright emissions in various solvents as well as in the solid state. These NCQDs exhibit multicolor PL emission across the visible region upon changing the environment (solutions and polymer matrices). NCQDs also exhibit excitation-dependent PL and solvatochromism, which have not been frequently investigated in CQDs. Most CQDs are nonemissive in the aggregated or solid state due to the aggregation-caused quenching (ACQ) effect, limiting their solid-state applications. However, NCQDs synthesized here display a strong solid-state emission centered at 568 nm attributed to the presence of surface functional groups that restrict the π-π interaction between the NCQDs and assist in overcoming the ACQ effect in the solid state. NCQD-containing gels display significant fluorescence enhancement in comparison to the NCQDs in 2-ethyl hexanol, likely because of the interaction between the polar PMMA blocks and NCQDs. The application of NCQDs-Gel as a solid/gel state fluorescent display has been presented. This research facilitates the development of large-scale, low-cost multicolor phosphor for the fabrication of optoelectronic devices, sensing, and bioimaging applications.

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.

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).

Fabrication of nitrogen-enriched carbon dots with green fluorescence for enzyme-free detection of uric acid

Based on the fact that UA directly quenched the green fluorescence of NCDs prepared at RT, a non-invasive sensor was developed.

One-pot synthesis of double silane-functionalized carbon dots with tunable emission and excellent coating properties for WLEDs application

Silane-functionalized carbon dots (SiCDs) can be exploited as effective color converting materials for the solid-state light-emitting devices. However, most of SiCDs reported thus far have shown photoluminescence emissions in the blue and green spectral range, which limit them to construct an efficient white light-emitting diodes (WLEDs) due to the lack of long-wavelength emission. Herein, a series of double silane-functionalized carbon dots (DSiCDs) were prepared via a one-step solvothermal method. The results show that the organic functional group of the silane has great influence on the optical properties of DSiCDs and the number of alkoxy group in the silane has great influence on coating properties of DSiCDs. In addition, the DSiCDs prepared by (3-aminopropyl)triethoxysilane and N-[3-(trimethoxysilyl)propyl]ethylenediamine with molar ratio of 7:3 show excellent optical properties with the maximum emission at 608 nm under 570 nm excitation. Furthermore, they can be completely cured within 1 h at room temperature to form fluorescent coating with high stability and strong adhesion to the substrate. Together with their excellent optical and coating properties, they can be directly coated on LED chips to prepare WLEDs, with a CIE coordinate of (0.33,0.31), color rendering index of 81.6, and color temperature of 5774 K.

The facile preparation of solid-state fluorescent carbon dots with a high fluorescence quantum yield and their application in rapid latent fingerprint detection

Because of direct π-π interactions and excessive energy resonance transfer, it is very challenging to prepare carbon dots (CDs) with a high fluorescence quantum yield (QY) in the solid state. In this study, novel CDs which gave solid-state fluorescence (SSF) with high brightness were successfully prepared via a simple microwave-assisted method. The prepared ScCDs can emit strong blue fluorescence in the solid state, and the absolute QY of this ScCDs powder reaches 51.7%. Such a high QY means that the ScCDs powder could be successfully applied in rapid latent fingerprint (LFP) detection. The LFP detection performance of this ScCDs powder was studied in detail, and the results show that the LFPs developed using the ScCDs powder can be visualized with high definition and contrast under different conditions. This research not only developed a new type of SSF-emitting CDs, but it also proved that the developed CDs have great potential for applications in LFP detection, and this research may also provide inspiration and ideas for the design of new SSF-emitting CDs.