Binary Host-induced Exciplex Enabled High Color-Rendering Index of 94 for Carbon Quantum Dot-Based White Light-Emitting Diodes

White light-emitting diodes (WLEDs) with high color-rendering index (CRI, >90) are important for backlight displays and solid-state lighting applications. Although the well-developed colloidal quantum dots (QDs) based on heavy metals such as cadmium and lead are promising candidates for WLEDs, the low CRI still remains a significant limitation. In addition, the severe toxicity of heavy metals greatly limits their widespread use. Herein, the study demonstrates low-cost and environmentally friendly carbon quantum dots (CQDs)-based WLEDs that exhibit a high CRI of 94.33, surpassing that of conventional cadmium/lead-containing QD-based WLEDs. This achievement is attained through the employment of a binary host-induced exciplex strategy. The high hole/electron mobility and suitable energy levels of the donor and acceptor give rise to a broadband orange-yellow emission stemming from the exciplex. As the host, the binary exciplex is capable of contributing blue and orange-yellow emission components while efficiently mitigating the aggregation-induced quenching of CQDs. Meanwhile, CQDs effectively address the deep-red emission gap, enabling the realization of CQDs-based WLEDs with high CRI. These WLEDs also exhibit a remarkably low turn-on voltage of 2.8 V, a maximum luminance exceeding 2000 cd m- 2, a correlated color temperature of 4976 K, and Commission Internationale de l'Eclairage coordinates of (0.34, 0.32).

Green to deep-red emissive carbon dot formation by C+ion implantation on nitrogen beam created self-masked nano-template

We report the formation of green to red emissive arrays of carbon dot on silicon-nitride nano-templates by successive implantation of nitrogen and carbon broad ion beams. The patterned nano-templates are formed by 14 keV N2+ion-bombardment at grazing incident (70°) on Si. Subsequently, 5 keV C+ions are implanted at the selective sites of the pyramidal nano-template by taking advantage of the self-masking effect. The nano-pyramidal pattern and the implanted carbon dots at the specific sites are confirmed by atomic force microscopy and cross sectional transmission electron microscopy measurements. The developed carbon dots (CDs) are mostly amorphous and consists of SiC and graphitic nitrogen (CN). G-band and D-band carbons are identified by Raman spectroscopy, while the presence of SiC and CN are detected by XPS measurements. A change of band-gap is observed for C-implanted templates by the UV-vis spectroscopy. Excitation wavelength-dependent photoemission from the dots is found in the green to red region. Maximum intense PL is observed in the green-orange region for excitation wavelength of 425 nm and a redshift of PL with decreasing intensity is observed with the increase of excitation wavelength. The observed photoluminescence is described in terms of the combined effects of quantum confinement, graphitic nitrogen and defect induced additional states formation in the carbon dots. The potential applications of CDs are also addressed.

White light emission from helically stacked humin-mimic based H-aggregates in heteroatom free carbon dots

White light emission (WLE), particularly from heteroatom free carbon dots (CDs), is unusual. Besides, deciphering the origin of WLE from a H-aggregated molecular fluorophore in such kinds of CDs is a challenging task due to their non-fluorescent character resulting from a forbidden transition from a lower-energy excitonic state. Therefore, rigorous investigation on their elusive excited state photophysical properties along with their steady-state optical phenomena has to be carried out to shed light on the nature of distinct emissive states formed in the CDs. Herein, for the first time, we report WLE from imperfect H-aggregates of co-facially π-π stacked humin-like structures comprising furfural monomer units as a unique molecular fluorophore in CDs, as revealed from combined spectroscopic and microscopic studies, synthesized through hydrothermal treatment of the single precursor, dextrose. H-aggregates in CDs show a broad range of excitation-dependent emission spectra with color coordinates close to pure white light, i.e., CIE (0.35, 0.37) and a color temperature of 6000 K. Imperfect orientation between the transition dipole moments of adjacent monomer units in the H-aggregate's molecular arrangement is expected to cause ground state symmetry breaking, as confirmed by Circular Dichroism (CD) studies, which established helically stacked nature in molecular aggregates and produced significant oscillatory strength at lower energy excitonic states to enable fluorescence. TRES and TAS investigations have been performed to minimise the intricacies associated with excited state photophysics, which is regarded as an essential step in gaining a grasp on emissive states. Based on the observation of two isoemissive spots in the time-resolved area normalized emission spectra (TRANES), the existence of three oligomeric species in the excited state equilibrium of the pure/hybrid H-aggregates has been established. The exciton dynamics through electron relaxation from the higher to the lower excitonic states, charge transfer (CT) states, and surface trap mediated emission in excimer states of H-aggregates have also been endorsed as three distinct emissive states from femtosecond transient absorption spectroscopy (TAS) studies corroborating with their steady-state absorption and emission behavior. The results would demonstrate the usage of CDs as a cutting-edge fluorescent material for creating aggregate-induced white light emission.

Strongly Emitting Folic Acid-Derived Carbon Nanodots for One- and Two-Photon Imaging of Lyotropic Myelin Figures

Non-invasive imaging of morphological changes in biologically relevant lipidic mesophases is essential for the understanding of membrane-mediated processes. However, its methodological aspects need to be further explored, with particular attention paid to the design of new excellent fluorescent probes. Here, we have demonstrated that bright and biocompatible folic acid-derived carbon nanodots (FA CNDs) may be successfully applied as fluorescent markers in one- and two-photon imaging of bioinspired myelin figures (MFs). Structural and optical properties of these new FA CNDs were first extensively characterized; they revealed remarkable fluorescence performance in linear and non-linear excitation regimes, justifying further applications. Then, confocal fluorescence microscopy and two-photon excited fluorescence microscopy were used to investigate a three-dimensional distribution of FA CNDs within the phospholipid-based MFs. Our results showed that FA CNDs are effective markers for imaging various forms and parts of multilamellar microstructures.

Enhanced Fluorescence and Environmental Stability of Red-Emissive Carbon Dots via Chemical Bonding with Cellulose Films

The development of red emission carbon dots with bright solid-state fluorescence would significantly broaden their application in optoelectronic devices and sensors. Herein, a red-emissive carbon dot-based nanocomposite has been synthesized through chemical bonding with cellulose films. The red emission originating from the surface states of carbon dots was maintained in the cellulose films. Due to the stable chemical bonding, the photoluminescence intensity and emission wavelength remained unchanged for 12 months, and the quantum yield of the composite was enhanced over 4 times. It also showed outstanding stability in water or weak acid-base environments under pHs ranging from 2 to 11. Therefore, the mechanism of chemical bonding that eliminated the defects and preserved the efficient radiative process through surface states was proposed.

Bright Electroluminescent White-Light-Emitting Diodes Based on Carbon Dots with Tunable Correlated Color Temperature Enabled by Aggregation

Carbon dots (CDs) as one of the most promising carbon-based nanomaterials are inspiring extensive research in optoelectronic applications. White-light-emitting diodes (WLEDs) with tunable correlated color temperatures (CCTs) are crucial for applications in white lighting. However, the development of high-performance CDs-based electroluminescent WLEDs, especially those with adjustable CCTs, remains a challenge. Herein, white CDs-LEDs with CCTs from 2863 to 11 240 K are successfully demonstrated by utilizing aggregation-induced emission red-shifting and broadening of CDs. As a result, a series of warm white, pure white, and cold white CDs-LEDs are realized with adjustable emissions in sequence along the blackbody radiation curve. These CDs-LEDs reach maximum brightness and external quantum efficiency up to 1414-4917 cd m^-2 and 0.08-0.87%, respectively, which is among the best performances of white CDs-LEDs. To the best of the authors' knowledge, this is the first time that CCT-tunable white electroluminescent CDs-LEDs are demonstrated through controlling the aggregation degrees of CDs.

Fluorescence turn-on immunosensing of HE4 biomarker and ovarian cancer cells based on target-triggered metal-enhanced fluorescence of carbon dots

Rapid and sensitive detection of tumor biomarkers and cancer cells is of crucial importance for the early diagnosis and prognosis prediction of cancer. The present report describes a target-induced fluorescence enhancement immunosensor that utilizes the optical property of carbon dots (CDs) and the metal-enhanced fluorescence effect (MEF) property of silver nanoparticles (AgNPs) for the sensitive detection of the cancer biomarker human epididymis protein 4 (HE4) and ovarian cancer cells. Nitrogen and sulfur co-doped CDs with a quantum yield of 85.6% were prepared and served as the fluorophore in MEF. The HE4 antibody (Ab) specific to the HE4 antigen was linked covalently to the surface of the synthesized CDs as the capture. The HE4 Ab-conjugated AgNPs (AgNPs-Ab) were prepared and utilized as signal amplification elements. In the presence of the target HE4, composite sandwich structures were formed between the labeled CDs-Ab and AgNPs-Ab, which brought the CDs and AgNPs into proximity, resulting in the fluorescence of CDs enhancement owing to MEF. The intensity of fluorescence enhancement was positively correlated with the HE4 concentration in the clinically important range of 0.01-200 nM with a limit detection of 2.3 pM. Moreover, the immunosensor was also successfully applied to specific fluorescence labeling and quantitative determination of HE4-positive ovarian cancer cells. The proposed target-triggered MEF sensor platform demonstrated high sensitivity, excellent anti-interference ability, along with successful validation in complex biological matrices, providing a new approach for HE4 detection in early diagnosis and therapeutic monitoring.

Tinospora cordifolia Leaves Derived Carbon dots for Cancer Cell Bioimaging, Free radical Scavenging, and Fe3+ Sensing Applications

Herein, we report the fabrication of Tinospora cordifolia leaves-derived carbon dots (TCLCDs) from aqueous extract of leaves as carbon source via simple, environmentally friendly, hydrothermal carbonization (HTC) technique. The synthesized TCLCDs were characterized for their physicochemical properties and further explored for in-vitro cancer cell bioimaging, radical scavenging, and metal ion sensing. The synthesized TCLCDs showed excitation-dependent emission property with maximum emission at 435 nm under the excitation of 350 nm. The High-Resolution Transmission Electron Microscopy (HRTEM) results revealed a roughly spherical shape with an average diameter of 5.47 nm. The diffused ring pattern of Selected Area Electron Diffraction (SAED) and halo diffraction pattern of X-ray diffraction (XRD) disclosed their amorphous nature. The Energy Dispersive X-ray (EDX) showed the existence of C, N, and O. The Fourier-transform infrared spectroscopy (FTIR) revealed the presence of -OH, -NH, -CN, and -CH groups. The TCLCDs showed excellent cellular biocompatibility with dose-dependent bioimaging results in melanoma (B16F10) and cervical cancer (SiHa) cell lines. Also, they exhibited excellent scavenging of free radicals with an IC₅₀ value of 0.524 mg/mL & selective Fe³⁺ ion sensing with a detection limit of 0.414 µM. Further, they exerted excellent bacterial biocompatibility, photostability, and thermal stability. The overall results reflected their potential for in-vitro cancer cell bioimaging, free radical scavenging, and selective Fe³⁺ ion sensing.

Luminescent Liquid Crystals Based on Carbonized Polymer Dots and Their Polarized Luminescence Application

Traditional luminescent liquid crystals (LLCs) suffer from fluorescence quenching caused by aggregation, which greatly limits their further application. In this work, a kind of novel LLCs (named carbonized polymer dot liquid crystals (CPD-LCs)) are designed and successfully synthesized through grafting the rod-shaped liquid crystal (LC) molecules of 4'-cyano-4-(4″-bromohexyloxy) biphenyl on the surface of CPDs. The peripheral LC molecules not only increase the distance between different CPDs to prevent them from aggregating and reduce intermolecular energy resonance transfer but also make this LLC have an ordered arrangement. Thus, the obtained CPD-LCs show good LC property and excellent high luminous efficiency with an absolute photoluminescence quantum yield of 14.52% in the aggregated state. Furthermore, this kind of CPD-LC is used to fabricate linearly polarized devices. The resultant linearly polarized dichroic ratio (N) and polarization ratio (ρ) are 2.59 and 0.44, respectively. Clearly, this type of CPD-LC shows promising applications for optical devices.

Langmuir and Langmuir Blodgett films of zinc oxide (ZnO) nanocrystals coated with polyhedral oligomeric silsesquioxanes (POSS)

HYPOTHESIS

The type and properties of ligands capping nanoparticles affect the characteristics of corresponding Langmuir and Langmuir-Blodgett films. When ligands are firmly anchored to the surface, as in zinc oxide nanocrystallites (ZnO NCs), compression at the air/water interface might cause ligands interdigitation and then the formation of supra-structures. Here, we evaluate how the introduction of bulky ligands, namely polyhedral oligomeric silsesquioxanes (POSSs), influences the self-assembly of POSS@ZnO NCs and the properties of corresponding thin films.

EXPERIMENTS

ZnO NCs capped with asymmetrical POSS derivatives are prepared via a one-pot two-step self-supporting organometallic (OSSOM) method. POSS@ZnO NCs are characterized by employing STEM, DLS, TGA, NMR, IR, UV-VIS, and photoluminescence spectroscopy. Changes in surface pressure, surface potential, and morphology (using BAM) are recorded upon compression at the air/water interface. Films transferred onto solid substrates are examined utilizing XRR and AFM.

FINDINGS

All studied POSS@ZnO NCs form stable Langmuir films. POSSs prevent the interdigitation of ligands capping neighboring NCs. Thus, POSS@ZnO NCs films resemble those composed of classical amphiphiles but without any visible structural source of amphiphilicity. We suggest that the core provides enough hydrophilicity to anchor NCs at the air/water interface. POSS ligands provide enough hydrophobicity for the NCs not to disperse into the subphase upon compression.

Carbon Dots Detect Water-to-Ice Phase Transition and Act as Alcohol Sensors via Fluorescence Turn-Off/On Mechanism

Highly fluorescent carbon nanoparticles called carbon dots (CDs) have been the focus of intense research due to their simple chemical synthesis, nontoxic nature, and broad application potential including optoelectronics, photocatalysis, biomedicine, and energy-related technologies. Although a detailed elucidation of the mechanism of their photoluminescence (PL) remains an unmet challenge, the CDs exhibit robust, reproducible, and environment-sensitive PL signals, enabling us to monitor selected chemical phenomena including phase transitions or detection of ultralow concentrations of molecular species in solution. Herein, we report the PL turn-off/on behavior of aqueous CDs allowing the reversible monitoring of the water-ice phase transition. The bright PL attributable to molecular fluorophores present on the CD surface was quenched by changing the liquid aqueous environment to solid phase (ice). Based on light-induced electron paramagnetic resonance (LEPR) measurements and density functional theory (DFT) calculations, the proposed kinetic model assuming the presence of charge-separated trap states rationalized the observed sensitivity of PL lifetimes to the environment. Importantly, the PL quenching induced by freezing could be suppressed by adding a small amount of alcohols. This was attributed to a high tendency of alcohol to increase its concentration at the CD/solvent interface, as revealed by all-atom molecular dynamics simulations. Based on this behavior, a fluorescence "turn-on" alcohol sensor for exhaled breath condensate (EBC) analysis has been developed. This provided an easy method to detect alcohols among other common interferents in EBC with a low detection limit (100 ppm), which has a potential to become an inexpensive and noninvasive clinically useful diagnostic tool for early stage lung cancer screening.

Long-wavelength emissive solid-state carbon dots in nanoporous glass with excellent thermal stability

Fluorescent solid-state carbon dots have drawn significant attention because of their intriguing optical properties, e.g., broad absorption, stable fluorescence, etc. However, obtaining the fluorescent solid-state carbon dots with a long-wavelength emission is still a challenging problem due to the notorious aggregation-induced quenching problem. In this paper, a technically feasible and low-cost approach for preparing fluorescent solid-state carbon dots is presented. The carbon dots are encapsulated in the nanoporous glass using the solution-phase-doping method. The size of nanoporous glass is tuned to 4.95 nm by regulating the ratio of boron to silicon to match the prepared CDs. Owing to the physical isolation and chemical connection of the -C-O-Si functional groups, the CDs are dispersed uniformly into the nanochannels of nanoporous glass. In this way, the aggregation-induced quenching problem of carbon dots is solved. The experiment results show that the photoluminescence has the excitation-independent emission at 609 nm, i.e., the prepared solid-state carbon dots are with orange fluorescence. More importantly, the solid-state carbon dots preserve orange fluorescence after heating treatment (400 °C) in the ambient atmosphere.

Concentration-dependent photoluminescence carbon dots for visual recognition and detection of three tetracyclines

Concentration-dependent photoluminescence carbon dots (CDs) have been successfully synthesized through the one-step hydrothermal treatment of o-phthalic acid and ethylenediamine. The CDs possessed higher fluorescence quantum yield, up to 39.22%, exhibiting distinguished optical property, water solubility, and stability. The CDs that emit strong blue-green fluorescence can visually identify and determine tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC). TC quenched the fluorescence of CDs at 500 nm owing to the inner filter effect; OTC behaved similarly, but the emission wavelength of CDs was red-shifted to 515 nm. Inversely, once CTC was introduced to CDs solution, the fluorescence increased and the emission peak was blue-shifted to 450 nm. Bandgap transition and electrostatic interaction were proposed to be the mechanisms for the detection of OTC and CTC by CDs. Wide linear relationships were established for TC, OTC, and CTC with the limits of detection to be 50 nM, 36 nM, and 373 nM, respectively. Furthermore, the nanoscale probe constructed by this system has been applied to detect tetracyclines (TCs) in complex samples with satisfying recoveries (93.2-114%) and was designed as a portable test strip sensor for visually on-site TCs of honey sample screening. Accordingly, the preparation process of the nano fluorescent probe is simple and environmentally friendly, and the probe has a specific recognition ability for tetracyclines. The synthesized CDs in this work provide a new orientation for fast, effective, and visual real-time detection of tetracycline in actual samples.

Ratiometric fluorescence resonance energy transfer aptasensor for highly sensitive and selective detection of Acinetobacter baumannii bacteria in urine sample using carbon dots as optical nanoprobes

Development of sensitive and selective analytical method for accurate diagnosis of Acinetobacter baumannii (Ab) bacteria in biological samples is a challenge. Herein, we developed an ingenious ratiometric fluorescent aptasensor for sensitive and selective detection of (Ab) bacteria based on fluorescence resonance energy transfer (FRET) between ortho-phenylenediamines carbon dot (o-CD), nitrogen-doped carbon nanodots (NCND) as donor's species and graphene oxide (GO) as acceptor. NCND that assembled onto the edge of graphene oxide (GO) exhibited quenched photoluminescence emission, and with the absorption of the modified o-CD with aptamer (o-CD-ssDNA) onto the graphene oxide surface the fluorescence of o-CD was efficiently quenched. The aptamer (ssDNA) as a biorecognition element is bound with A. baumannii specifically which releases the o-CD-ssDNA from GO and the recovery of the fluorescence signal of o-CD, while the fluorescence intensity of NCND only slightly altered and acted as the reference signal in ratiometric fluorescence assay. The fluorescence intensity ratio (I₅₅₀ nm/I₄₄₀nm) varied from 2.0 to 10.0 with the concentration of bacteria changing from 2.0 × 10³ to 4.5 × 10⁷ cfu/mL and the low detection limit of 3.0 × 10² cfu/mL (S/N = 3). The feasibility of the developed aptasensor for selective detection of A. baumannii in urine sample with satisfactory results was also demonstrated.

Carbon Dot-Based Composite Films for Simultaneously Harvesting Raindrop Energy and Boosting Solar Energy Conversion Efficiency in Hybrid Cells

Energy harvesting has drawn worldwide attention as a sustainable technology, while combining several approaches in a single device to maximize the overall energy output holds great promise to offer valuable technologies able to alleviate the energy crisis. Here, we present a hybrid cell composed of a silicon solar cell and a water-droplet-harvesting triboelectric nanogenerator (WH-TENG) with the capacity of harvesting both solar and raindrop energies. A transparent and solution processable carbon dot-based composite film is introduced as a dual-functional layer, acting as the transmittance enhancement layer of the solar cell as well as an ionic conductor of the WH-TENG. At an optimal loading of carbon dots in the composite, the significant enhancement of transmittance in visible spectral range increases the short-circuit current density of the solar cell, which results in an increase of its power conversion efficiency from 13.6% to 14.6%. In addition, the transparent WH-TENG consisting of fluorinated ethylene propylene as a triboelectrification layer can generate a maximum power of 13.9 μW by collecting raindrop energy. This study provides a promising strategy to boost the energy conversion through multiple sources with the aid of a dual-functional layer for enhancing solar cell performance as well as harvesting raindrop energy.

Recent Advances in Energy Conversion Applications of Carbon Dots: From Optoelectronic Devices to Electrocatalysis

Exploitation and utilization of sustainable energy sources has increasingly become the common theme of global social development, which has promoted tremendous development of energy conversion devices/technologies. Owing to excellent and unique optical/electrical properties, carbon dots (CDs) have attracted extensive research interest for numerous energy conversion applications. Strong absorption, downconversion photoluminescence, electron acceptor/donor characteristics, and excellent electron conductivity endow CDs with enormous potential for applications in optoelectronic devices. Furthermore, excellent electron transfers/transport capacities and easily manipulable structural defects of CDs offer distinct advantages for electrocatalytic applications. Recent advances in CD-based energy conversion applications, including optoelectronic devices such as light-emitting diodes and solar cells, and electrocatalytic reactions including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, and carbon dioxide reduction reaction, are summarized. Finally, current challenges and future prospects for CD-based energy conversion applications are proposed, highlighting the importance of controllable structural design and modifications.

Sonochemical synthesis of carbon dots, mechanism, effect of parameters, and catalytic, energy, biomedical and tissue engineering applications

Carbon-based nanomaterials are gaining more and more interest because of their wide range of applications. Carbon dots (CDs) have shown exclusive interest due to unique and novel physicochemical, optical, electrical, and biological properties. Since their discovery, CDs became a promising material for wide range of research applications from energy to biomedical and tissue engineering applications. At same time several new methods have been developed for the synthesis of CDs. Compared to many of these methods, the sonochemical preparation is a green method with advantages such as facile, mild experimental conditions, green energy sources, and feasibility to formulate CDs and doped CDs with controlled physicochemical properties and lower toxicity. In the last five years, the sonochemically synthesized CDs were extensively studied in a wide range of applications. In this review, we discussed the sonochemical assisted synthesis of CDs, doped CDs and their nanocomposites. In addition to the synthetic route, we will discuss the effect of various experimental parameters on the physicochemical properties of CDs; and their applications in different research areas such as bioimaging, drug delivery, catalysis, antibacterial, polymerization, neural tissue engineering, dye absorption, ointments, electronic devices, lithium ion batteries, and supercapacitors. This review concludes with further research directions to be explored for the applications of sonochemical synthesized CDs.

Self-formed C-dot-based 2D polysiloxane with high photoluminescence quantum yield and stability

C-Dots and composites based on them face the challenges of poor stability, especially under photo-radiation, and low solid-state photoluminescence quantum yields (PLQYs), which hinder their application in optical devices. Herein, a novel 2-dimensional hybrid material of polysiloxane embedded with Si-doped carbon dots (P-E-Si-CDs) was synthesized by a self-assembly approach, and the hybrid composite exhibited broadband blue-green fluorescence emission, outstanding photostability, high thermal stability, and a high PLQY of 82.8%. Moreover, the dual fluorescent emissions were demonstrated the creation of two closed-loop fluorophores. Using the as-prepared hybrid fluorescent material, fabricated light-emitting diodes (LEDs) based on UV and blue-emitting LED chips present safe warm white light emission and adjustable white emission with a high color rendering index of up to 91, respectively. This work provides a novel strategy for the design and realization of Si-CD-based hybrid composites, thus promising their prospective use commercially in LED lighting.

In situ synthesis of stretchable and highly stable multi-color carbon-dots/polyurethane composite films for light-emitting devices

Multi-color-emissive fluorescent polymer nanocomposite films have potential applications in optoelectronic devices. Herein, stretchable, mechanically stable multi-color carbon-dots-based films are in situ fabricated by condensation and aging of carboxylated polyurethane in the presence of various carbon sources. As-prepared CDs/PU films emit different colors covering from blue (414 nm) to red (620 nm) by tuning reaction conditions. Moreover, CDs are fixed and have good dispersion in the PU matrix due to the interactions of amine groups from the carbon sources with the carboxylate group of PU. Thus, phase separation of composite films can be avoided. And, more than 90% of their emission intensity is preserved after soaking in water for 30 days, aging for up to 6 h at 100 °C, and subjecting to several cycles of stretching and natural recovery. These advantages are encouraging for the use of CDs/PU composite films in solid-state lighting applications. Remote multi-color LEDs have been fabricated by placing a down-conversion layer of CDs/PU films separated through coating them on the same chips (emission at 365 nm), with Commission Internationale de l'Eclairage color coordinates of (0.22, 0.23), (0.43, 0.53), (0.49, 0.46), and (0.41, 0.28), respectively.

Stretchable, mechanically stable multi-color carbon-dots-based polymer films are in situ fabricated, and showed potential for application in optoelectronic devices.

Enhancement of Fluorescence Emission for Tricolor Quantum Dots Assembled in Polysiloxane toward Solar Spectrum-Simulated White Light-Emitting Devices

Commercial white light-emitting diodes (LEDs) have the undesirable characteristics of blue-rich emission and low color rendering index (CRI), while the constituent quantum dots (QDs) suffer from aggregation-induced fluorescence quenching and poor stability. Herein, a strategy is developed to assemble tricolor QDs into a polysiloxane matrix using a polymer-mediated hybrid approach whereby the hybrid composite exhibits a significant enhancement of aggregation-dispersed emission, outstanding photostability, high thermal stability, and outstanding fluorescence recovery. Using the as-prepared hybrid fluorescent materials, the fabricated LEDs exhibit solar spectrum-simulated emission with adjustable Commission Internationale de L'Eclairage coordinates, correlated color temperature, and a recorded CRI of 97. Furthermore, they present no ultraviolet emission and weak blue emission, thus indicating an ideal healthy and high-CRI white LED lighting source.

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.

Progress in the Synthesis of Bifunctionalized Polyhedral Oligomeric Silsesquioxane

Polyhedral oligomeric silsesquioxane (POSS) has been considered as one of the most promising nanofillers in academic and industrial research due to its unique multifunctional nanostructure, easy functionalization, hybrid nature, and high processability. The progress of POSS has been extensive, particularly applications based on single- or multiple-armed POSS. In polymer hybrids, in order to enhance the properties, bifunctional POSS has been incorporated into the backbone chain of the polymer. This review summarizes recent developments in the synthesis, modification, and application of bifunctional POSS-containing composite materials. This includes amino-POSS, hydroxyl-POSS, aromatic ring-POSS, ether-POSS, and vinyl groups-POSS and their applications, exemplified by polyurethanes (PUs) and polyimides (PIs). In addition, the review highlights the enhancement of thermal, mechanical, and optical properties of the composites.

Chemically Synthesized Carbon Nanorods with Dual Polarized Emission

We realized the synthesis of carbon nanorods-monodisperse colloidal particles with a length of 50 nm and a width of 20 nm-which can be considered an addition to the family of light-emitting carbon-based nanostructures. Their anisotropic shape is determined by the use of the surfactant aminopropylisobutyl polyhedral oligomeric silsesquioxane, and their optical properties originate from domains of polycyclic aromatic hydrocarbons incorporated within an inorganic framework. The nanorods show dual polarized emission with a quantum yield of 15-20% and emission anisotropy of ∼0.3, which changes from blue (460 nm) to yellow (565 nm) depending on the excitation wavelength. These carbon nanorods expand the range of light-emitting carbon nanomaterials available for optoelectronic and biolabeling applications.

sp2-sp3-Hybridized Atomic Domains Determine Optical Features of Carbon Dots

Carbon dots (CDots) are a promising biocompatible nanoscale source of light, yet the origin of their emission remains under debate. Here, we show that all the distinctive optical properties of CDots, including the giant Stokes shift of photoluminescence and the strong dependence of emission color on excitation wavelength, can be explained by the linear optical response of the partially sp²-hybridized carbon domains located on the surface of the CDots' sp³-hybridized amorphous cores. Using a simple quantum chemical approach, we show that the domain hybridization factor determines the localization of electrons and the electronic bandgap inside the domains and analyze how the distribution of this factor affects the emission properties of CDots. Our calculation data fully agree with the experimental optical properties of CDots, confirming the overall theoretical picture underlying the model. It is also demonstrated that fabrication of CDots with large hybridization factors of carbon domains shifts their emission to the red side of the visible spectrum, without a need to modify the size or shape of the CDots. Our theoretical model provides a useful tool for experimentalists and may lead to extending the applications of CDots in biophysics, optoelectronics, and photovoltaics.

Deep-Ultraviolet Emissive Carbon Nanodots

Deep-ultraviolet (DUV) emissive carbon nanodots (CNDs) have been designed theoretically and demonstrated experimentally based on the results of first-principles calculations using the density functional theory method. The emission of the CNDs is located in the range from 280 to 300 nm, which coincides well with the results of theoretical calculation results. The photoluminescence (PL) quantum yield (QY) of the CNDs is up to 31.6%, and the strong emission of the CNDs originates from core-state (π-π*) carriers' radiative recombination and surface passivation. Benefiting from the core-state emission and surface group passivation, the emission of the CNDs is independent of the excitation wavelength and ambient solvent. DUV light-emitting diodes (LEDs) have been fabricated based on the DUV emissive CNDs, and the LEDs can be used as the excitation source to excite blue, green, and red CNDs, indicating their potential application in DUV light sources. This work may provide a clue for the designing and realizing of DUV emissive CNDs, thus promising the potential application of CNDs in DUV light-emitting sources.

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.

A Facile Approach to Solid-State White Emissive Carbon Dots and Their Application in UV-Excitable and Single-Component-Based White LEDs

Large-scale applications of conventional rare-earth phosphors in white light-emitting diodes (W-LEDs) are restricted by the non-renewable raw material sources and high energy consumption during the production process. Recently, carbon dots (CDs) have been proposed as promising alternatives to rare-earth phosphors and present bright prospects in white lighting. However, the use of CDs in W-LEDs still has two major obstacles, i.e., solid-state quenching and lack of single-component white emissive products. In this work, a facile, rapid, and scalable method for the preparation of solid-state white emissive CDs (W-CDs) is reported via microwave-irradiation heating of L-aspartic acid (AA) in the presence of ammonia. The W-CDs exhibit blue photoluminescence (PL) in dilute aqueous dispersion and their emission spectra gradually broaden (emerging new emissions at orange-yellow regions) with concentration increases. Interestingly, the W-CDs powder displays a very broad PL spectrum covering nearly the whole visible-light region under ultraviolet (UV) excitation, which is responsible for the observed white emission. Further studies revealed that the self-quenching-resistance feature of the W-CDs is probably due to a covering of polymer-like structures on their surface, thus avoiding the close contact of nanoparticles with each other. PL emission of the W-CDs is reasonably ascribed to a cross-linked enhanced effect (CEE) of the sub-fluorophores contained in the material (e.g., –NH₂ and C=O). Finally, applications of the W-CDs in fabricating single-component-based W-LEDs using commercially available UV chips were attempted and shown to exhibit satisfactory performances including high white light-emitting purity, high color rendering index (CRI), and tunable correlated color temperature (CCT), thus rendering great promise for W-CDs in the field of white lighting.

Temperature-controlled spectral tuning of full-color carbon dots and their strongly fluorescent solid-state polymer composites for light-emitting diodes

The development of full-color/white carbon-dot-based light-emitting diodes (LEDs) has been achieved, which show promising applications in full-color and flexible displays, backlights, and novel lighting sources. The gram-level synthesis of these full-color carbon dots (CDs) from citric acid by controlling the temperature has been achieved. By increasing the temperature from 120 to 180 °C, two, four, and six light-emitting CDs can be obtained, for which the emission wavelength shifts from 440 to 585 nm. This result reveals that temperature has a huge impact on the evolution of surface states, that is, increasing the temperature brings about enhanced surface functionalization and passivation, resulting in a red shift of the emission wavelength and enhancement of quantum yield. Then, full-color CDs/polymer composite phosphors are fabricated for efficient phosphor-based LED devices with quench-resistant solid-state fluorescence. By regulating the proportion of various CDs/polymer phosphors, white LEDs are realized with Commission Internationale de L'Eclairage coordinates of (0.32, 0.33) and a color rendering index of 82.7. The as-prepared CD-based full/white color LEDs can prove to be promising candidates for alternative light sources.

Carbon dots produced via space-confined vacuum heating: maintaining efficient luminescence in both dispersed and aggregated states

Aggregation-induced quenching (AIQ) of emission is an obstacle for the development of carbon dots (CDots) for solid-state luminescent devices. In this work, we introduce a method to avoid AIQ and to produce highly luminescent CDots through a space-confined vacuum heating synthesis. In the presence of CaCl₂, a mixture of citric acid and urea forms an inflated foam under vacuum heating at 120 °C. Upon gradually increasing the heating temperature to 250 °C, blue emissive molecular species are first formed, and are then transformed into uniform-sized green emissive CDots through dehydration and carbonization processes taking place in the confined ultrathin spaces of the foam walls. The green luminescence of these CDots originates from conjugated sp² domains, and these CDots exhibit a high photoluminescence quantum yield (PLQY) of 72% in ethanol solution. Remarkably, due to the existence of only one type of recombination center in these nanoparticles, AIQ does not take place in CDot-based close-packed films, which show strong emission with a PLQY of 65%. Utilizing the differences in the emission properties of vacuum heating produced CDots, CDots synthesized through microwave-assisted heating, and commercial green fluorescent organic ink (namely, excitation-dependent vs. excitation-independent emission, and different stability against photobleaching), multilevel data encryption has been demonstrated.

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.

Carbon Dot Fluorescence-Lifetime-Encoded Anti-Counterfeiting

Carbon dots (CDs) rank among the most promising luminescent nanomaterials for anti-counterfeiting application owing to their high fluorescence quantum yield and nontoxicity. Herein, we report a novel, high-level security performance anti-counterfeiting strategy achieved by fluorescence-lifetime-encoded CD fluorescent inks. CD-inks have identical steady-state emission properties, but they have distinctive and well-separated fluorescence lifetimes, allowing authentication of security tags using exclusively fluorescence lifetime imaging. A proof-of-concept anti-counterfeiting tag using CD-based lifetime-encoded inks is demonstrated. The developed CD lifetime-based anti-counterfeit technology is awaited to be applicable to a wide spectrum of security-protecting purposes. Furthermore, the presented method can be easily extended to integrate fluorescence-lifetime-encoded CDs in multichannel bioimaging, high-throughput flow cytometry, and optical data storage.

Hydrogen Peroxide-Treated Carbon Dot Phosphor with a Bathochromic-Shifted, Aggregation-Enhanced Emission for Light-Emitting Devices and Visible Light Communication

It is demonstrated that treatment of blue-emissive carbon dots (CDs) with aqueous hydrogen peroxide (H2O2) results in the green emissive solid state CD phosphor with photoluminescence quantum yield of 25% and short luminescence lifetime of 6 ns. The bathochromic-shifted, enhanced green emission of H2O2-treated CDs in the powder is ascribed to surface state changes occurring in the aggregated material. Using the green emissive H2O2-treated CD phosphor, down-conversion white-light-emitting devices with cool, pure, and warm white light are fabricated. Moreover, using the green emissive CD phosphor as a color converter, a laser-based white-light source is realized, and visible light communication with a high modulation bandwidth of up to 285 MHz and data transmission rate of ≈435 Mbps is demonstrated.

Malic Acid Carbon Dots: From Super-resolution Live-Cell Imaging to Highly Efficient Separation

As-synthesized malic acid carbon dots are found to possess photoblinking properties that are outstanding and superior compared to those of conventional dyes. Considering their excellent biocompatibility, malic acid carbon dots are suitable for super-resolution fluorescence localization microscopy under a variety of conditions, as we demonstrate in fixed and live trout gill epithelial cells. In addition, during imaging experiments, the so-called "excitation wavelength-dependent" emission was not observed for individual as-made malic acid carbon dots, which motivated us to develop a time-saving and high-throughput separation technique to isolate malic acid carbon dots into fractions of different particle size distributions using C₁₈ reversed-phase silica gel column chromatography. This post-treatment allowed us to determine how particle size distribution influences the optical properties of malic acid carbon dot fractions, that is, optical band gap energies and photoluminescence behaviors.

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

The past few years have witnessed the rapid development of carbon dots (CDs) due to their outstanding optical properties and a wide range of applications. However, the design and control of CDs with long-wavelength multicolor emission are still huge challenges to be addressed for their practical use in different fields. Here, novel nitrogen-doped multiple-core@shell-structured AC-CDs with tricolor emissions of red, green, and blue were constructed via one-pot hydrothermal method from 5-amino-1,10-phenanthroline and citric acid as reactants and the growth process of AC-CDs was monitored with the reaction time in the synthetic system. The origin of different fluorescence emissions was explored using the unique coordination ability of the surface groups of AC-CDs. An obvious concentration dependence of fluorescent properties was observed for the as-prepared AC-CDs, and a highly fluorescent quantum yield (QY) of 67% for red emission at 630 nm can be obtained by adjusting concentration of AC-CDs. The pure white-light emission (0.33, 0.33; Commission Internationale de l'Elcairage coordinate) was carried out from single carbon dot with QY of 29% through regulation of the excitation and concentration of multiple-core@shell-structured AC-CDs. In addition, because of their excellent photoluminescent properties, the white-emitting AC-CDs as emitting phosphor can be easily used in the fabrication of white-light-emitting diode with good anti-photobleaching and temperature stability.

Red carbon dots-based phosphors for white light-emitting diodes with color rendering index of 92

Exploration of solid-state efficient red emissive carbon dots (CDs) phosphors is strongly desired for the development of high performance CDs-based white light-emitting diodes (WLEDs). In this work, enhanced red emissive CDs-based phosphors with photoluminescence quantum yields (PLQYs) of 25% were prepared by embedding red emissive CDs (PLQYs of 23%) into polyvinyl pyrrolidone (PVP). Because of the protection of PVP, the phosphors could preserve strong luminescence under long-term UV excitation or being mixed with conventional packaging materials. By applying the red emissive phosphors as the color conversion layer, WLEDs with high color rendering index of 92 and color coordinate of (0.33, 0.33) are fabricated.

Supramolecular Cross-Link-Regulated Emission and Related Applications in Polymer Carbon Dots

Involvement of clear photoluminescence (PL) mechanism in specific chemical structure is at the forefront of carbon dots (CDs). Supramolecular interaction exists in plenty of materials, offering an inherent way to administrate the optical and photophysical properties, especially in terms of newly developed polymer carbon dots (PCDs). However, supramolecular-interaction-derived PL regulation is always ignored in the shadow of many kinds of PL factors, and we still have a limited understanding on the distinct chemical structure and mechanism of supramolecular effect in PCDs. Herein, several distinct photoluminescent phenomena of PCDs under aqueous and solid state are reviewed in terms of supramolecular cross-linking, with highly emphasizing the importance of supramolecular cross-link-enhanced emission (SCEE) effects, and the regulated function of supramolecular interaction's intensity and types between PCDs for special PL behaviors of PCDs. In addition, we categorize the photoluminescent phenomena in PCDs into the following aspects: supramolecular cross-link-enhanced dilute-solution-state emission, concentration-controlled multicolor emission, supramolecular regulation for quenching-resistant solid-state fluorescence, as well as supramolecular cross-link-assisted room-temperature- phosphorescence (RTP) under solid states. Furthermore, the applications of PCDs in light-emitting diodes (LED), solar cells, and anticounterfeiting and data encryption, etc., are presented, based on the distinct supramolecular cross-link-regulated photoluminescent phenomena, especially the solid-state emission. Finally, a brief outlook is given, highlighting the currently existing problems and development direction of supramolecular cross-link-regulated emission in PCDs.

Sol-Gel Chemistry for Carbon Dots

Carbon dots are an emerging class of carbon-based nanostructures produced by low-cost raw materials which exhibit a widely-tunable photoluminescence and a high quantum yield. The potential of these nanomaterials as a substitute of semiconductor quantum dots in optoelectronics and biomedicine is very high, however they need a customized chemistry to be integrated in host-guest systems or functionalized in core-shell structures. This review is focused on recent advances of the sol-gel chemistry applied to the C-dots technology. The surface modification, the fine tailoring of the chemical composition and the embedding into a complex nanostructured material are the main targets of combining sol-gel processing with C-dots chemistry. In addition, the synergistic effect of the sol-gel precursor combined with the C-dots contribute to modify the intrinsic chemo-physical properties of the dots, empowering the emission efficiency or enabling the tuning of the photoluminescence over a wide range of the visible spectrum.

The synthesis of green fluorescent carbon dots for warm white LEDs

Green emissive carbon dots synthesized by solvothermal method is used for warm white light-emitting devices.

Confined Synthesis of Carbon Nitride in a Layered Host Matrix with Unprecedented Solid-State Quantum Yield and Stability

Fluorescent carbon nanomaterials have drawn tremendous attention for their intriguing optical performances, but their employment in solid-state luminescent devices is rather limited as a result of aggregation-induced photoluminescence quenching. Herein, ultrathin carbon nitride (CN) is synthesized within the 2D confined region of layered double hydroxide (LDH) via triggering the interlayer condensation reaction of citric acid and urea. The resulting CN/LDH phosphor emits strong cyan light under UV-light irradiation with an absolute solid-state quantum yield (SSQY) of 95.9 ± 2.2%, which is, to the best of our knowledge, the highest value of carbon-based fluorescent materials ever reported. Furthermore, it exhibits a strong luminescence stability toward temperature, environmental pH, and photocorrosion. Both experimental studies and theoretical calculations reveal that the host-guest interactions between the rigid LDH matrix and interlayer carbon nitride give the predominant contribution to the unprecedented SSQY and stability. In addition, prospective applications of the CN/LDH material are demonstrated in both white light-emitting diodes and upconversion fluorescence imaging of cancer cells.

Synthesis of multi-functional green fluorescence carbon dots and their applications as a fluorescent probe for Hg2+ detection and zebrafish imaging

Green fluorescence carbon dots for mercury detection and zebrafish imaging.

53% Efficient Red Emissive Carbon Quantum Dots for High Color Rendering and Stable Warm White-Light-Emitting Diodes

Red emissive carbon quantum dots (R-CQDs) with quantum yield of 53% is successfully prepared. An ultraviolet (UV)-pumped CQD phosphors-based warm white light-emitting diode (WLED) is realized for the first time and achieves a color rendering index of 97. This work provides a new avenue for the exploration of low cost, environment-friendly, and high-performance CQD phosphors-based warm WLEDs.

Simple Microwave-Assisted Synthesis of Amphiphilic Carbon Quantum Dots from A3/B2 Polyamidation Monomer Set

Highly fluorescent and amphiphilic carbon quantum dots (CQDs) were prepared by microwave-assisted pyrolysis of citric acid and 4,7,10-trioxa-1,13-tridecanediamine (TTDDA), which functioned as an A₃ and B₂ polyamidation type monomer set. Gram quantities of fluorescent CQDs were easily obtained within 5 min of microwave heating using a household microwave oven. Because of the dual role of TTDDA, both as a constituting monomer and as a surface passivation agent, TTDDA-based CQDs showed a high fluorescence quantum yield of 29% and amphiphilic solubility in various polar and nonpolar solvents. These properties enable the wide application of TTDDA-based CQDs as nontoxic bioimaging agents, nanofillers for polymer composites, and down-converting layers for enhancing the efficiency of Si solar cells.