Carbon dots (CDs) represent a recently emerged class of luminescent materials with a great potential for biomedical theranostics, and there are a lot of efforts to shift their absorption and emission ...toward deep‐red (DR) to near‐infrared (NIR) region falling in the biological transparency window. This review offers comprehensive insights into the synthesis strategies aimed to achieve this goal, and the current approaches of modulating the optical properties of CDs over the DR to NIR region. The underlying mechanisms of their absorption, photoluminescence, and chemiluminescence, as well as the related photophysical processes of photothermal conversion and formation of reactive oxygen species are considered. The already available biomedical applications of CDs, such as in the photoacoustic imaging and photothermal therapy, photodynamic therapy, and their use as bioimaging agents and drug carriers are then shortly summarized.
Carbon dots (CDs) with optical transitions in deep‐red to near‐infrared spectral range have experienced a rapid development within recent years. This review provides comprehensive insights into the current approaches of modulating the optical properties of such CDs, emphasizes the underlying mechanisms and related photophysical processes, and shortly summarizes their related biomedical applications.
It is important to reveal the luminescence mechanisms of carbon dots (CDs). Herein, CDs with two types of optical centers are synthesized from citric acid in formamide by a solvothermal method, and ...show high photoluminescence quantum yield reaching 42%. Their green/yellow emission exhibits pronounced vibrational structure and high resistance toward photobleaching, while broad red photoluminescence is sensitive to solvents, temperature, and UV–IR. Under UV–IR, the red emission is gradually bleached due to the photoinduced dehydration of the deprotonated surface of CDs in dimethyl sulfoxide, while this process is hindered in water. From the analysis of steady‐state and time‐resolved photoluminescence and transient absorption data together with density functional theory calculations, the green/ yellow emission is assigned to conjugated sp2‐domains (core state) similar to organic dye derivatives stacked within disk‐shaped CDs; and the broad red emission—to oxygen‐containing groups bound to sp2‐domains (surface state), whereas energy transfer from the core to the surface state can happen.
Based on comprehensive analysis of structural and optical properties of carbon dots, their multicolor emission centers are assigned. The green/yellow emission comes from conjugated sp2‐domains (core state) similar to organic dye derivatives stacked within disk‐shaped carbon dots; and the broad red emission—from oxygen‐containing groups bound to sp2‐domains (surface state), whereas energy transfer from the core to surface states can happen.
A seeded growth method to produce colloidal carbon dots (CDs) through controlling the number of seeds and reaction time, which is demonstrated to be an effective way to tune their optical properties, ...is developed. Color‐tunable fluorescence of CDs with blue, green, yellow, and orange emissions under UV excitation is achieved by increasing the size of the seed CDs, with the color depending on the size of the π‐conjugated domains. Strong multicolor photoluminescence of powdered samples enables realization of efficient down‐conversion white‐light‐emitting devices with correlated color temperature ranging from 9579 to 2752 K and luminous efficacy from 19 to 51 lm W−1. Moreover, color‐tunable room‐temperature phosphorescence of CD powders is demonstrated in the broad spectral range of 500–600 nm. It is related to the presence of the nitrogen‐containing groups at the surface of CDs, which form interparticle hydrogen bonds to protect the CD triplet states from quenching, and to the existence of the polyvinylpyrrolidone polymer chains at the surface of CDs. The color‐tunable room‐temperature phosphorescence from CDs demonstrated in this work exhibits potential for data encryption.
Both the number of seeds added to the reaction mixture and the reaction time affect the diameter of carbon dot samples, which is related to the degree of extent of their π‐conjugated domains, governing their emission color. The bottom part of the table of contents image shows photographs of the phosphorescent powders taken at different UV excitation delay times.
Carbon dot (CD) based long‐lived afterglow emission materials have attracted attention in recent years, but demonstration of white‐light room‐temperature afterglow remains challenging, due to the ...difficulty of simultaneous generation of multiple long‐lived excited states with distinct chromatic emission. In this work, a white‐light room‐temperature long‐lived afterglow emission from a CD powder with a high efficiency of 5.8% and Commission International de l'Eclairage (CIE) coordinates of (0.396, 0.409) is realized. The afterglow of the CDs originates from a synergy between the phosphorescence of the carbon core and the delayed fluorescence associated with the surface CN moieties, which is accomplished by matching the singlet state of the surface groups of the CDs with the long‐lived triplet state of the carbon core, resulting in an efficient energy transfer. It is demonstrated how the long‐lived afterglow emission of CDs can be utilized for fabrication of white light emitting devices and in anticounterfeiting applications.
Carbon dots exhibit a bright white‐light room‐temperature afterglow, which is a result of a synergistic effect between the phosphorescence of the carbon core and the delayed fluorescence of the surface CN moieties.
Carbon dots (CDs) are light-emitting nanoparticles that show great promise for applications in biology and medicine due to the ease of fabrication, biocompatibility, and attractive optical ...properties. Optical chirality, on the other hand, is an intrinsic feature inherent in many objects in nature, and it can play an important role in the formation of artificial complexes based on CDs that are implemented for enantiomer recognition, site-specific bonding, etc. We employed a one-step hydrothermal synthesis to produce chiral CDs from the commonly used precursors citric acid and ethylenediamine together with a set of different chiral precursors, namely, L-isomers of cysteine, glutathione, phenylglycine, and tryptophan. The resulting CDs consisted of O,N-doped (and also S-doped, in some cases) carbonized cores with surfaces rich in amide and hydroxyl groups; they exhibited high photoluminescence quantum yields reaching 57%, chiral optical signals in the UV and visible spectral regions, and two-photon absorption. Chiral signals of CDs were rather complex and originated from a combination of the chiral precursors attached to the CD surface, hybridization of lower-energy levels of chiral chromophores formed within CDs, and intrinsic chirality of the CD cores. Using DFT analysis, we showed how incorporation of the chiral precursors at the optical centers induced a strong response in their circular dichroism spectra. The optical characteristics of these CDs, which can easily be dispersed in solvents of different polarities, remained stable during pH changes in the environment and after UV exposure for more than 400 min, which opens a wide range of bio-applications.
In this work, we report a successful extension of the family of light-emitting colloidal carbon nanostructures to a number of different shapes and morphologies, namely, carbon nanorolls (CNRs) and ...carbon nanobelts (CNBs). Near infrared (NIR)-emissive CNRs were synthesized via a solvothermal fusion of carbon dots (CDs) triggered by a dehydration process of their surface functional groups. They appear in a form of short cylinders, with diameters ranging from 20 to 40 nm and cylinder lengths ranging from 7 to 20 nm. In ethanol solution, CNRs have a maximum absorption peak at 665 nm and a NIR emission band extending from 650 to 800 nm, with a photoluminescence quantum yield of 9.2%. Intriguingly, the rolled structure of CNRs can be uncoiled under 655 nm laser irradiation (power density 1 W·cm–2) of their solution in ethanol, forming CNBs with a width of 7–20 nm and lengths reaching several hundreds of nanometers, which is accompanied by a considerably decreased absorption band at 665 nm and a decreased NIR emission. This unfolding is ascribed to the decrease of the strength of interlayer hydrogen bonding, owing to the photothermally induced dehydration and further carbonization of the CNRs. Alongside the decreased NIR emission, CNBs exhibit enhanced green and red emissions under UV and green light excitation, respectively, which allows us to demonstrate multiple-level luminescence encryptions on a paper stamped with CNR- and CNB-inks.
Subwavelength particles supporting Mie resonances underpin a strategy in nanophotonics for efficient control and manipulation of light by employing both an electric and a magnetic optically induced ...multipolar resonant response. Here, we demonstrate that monolithic dielectric nanoparticles made of CsPbBr3 halide perovskites can exhibit both efficient Mie-resonant lasing and structural coloring in the visible and near-IR frequency ranges. We employ a simple chemical synthesis with nearly epitaxial quality for fabricating subwavelength cubes with high optical gain and demonstrate single-mode lasing governed by the Mie resonances from nanocubes as small as 310 nm by the side length. These active nanoantennas represent the most compact room-temperature nonplasmonic nanolasers demonstrated until now.
Metal halide perovskite‐based optoelectronics has experienced an unprecedented development in the last decade, while further improvements of efficiency, stability, and economic gains of such devices ...require novel engineering concepts. The use of carbon nanoparticles as versatile auxiliary components of perovskite‐based optoelectronic devices is one strategy that offers several advantages in this respect. In this review, first, a brief introduction is offered on metal halide perovskites and on the major performance characteristics of related optoelectronic devices. Then, the versatility and merits of different kinds of carbon nanoparticles, such as graphene quantum dots and carbon dots, are discussed. The tunability of their electronic properties is focused upon, their interactions with perovskite components are analyzed, and different strategies of their implementation in optoelectronic devices are introduced, which include solar cells, light‐emitting diodes, luminescent solar concentrators, and photodetectors. It is shown how carbon nanoparticles influence charge carriers extraction and transport, promote perovskite crystallization, allow for efficient passivation, block ion migration, suppress hysteresis, enhance their environmental stability, and thus improve the performance of perovskite‐based optoelectronic devices.
Carbon nanoparticles can serve as versatile auxiliary components for metal halide perovskites: they promote crystallization, passivate defects, tune charge transfer/transport characteristics, and improve the performance of perovskite‐based optoelectronic devices. This review focuses on the tunability of the electronic properties of carbon nanoparticles such as graphene quantum dots and carbon dots, analyzes their interactions with perovskite components, and introduces different strategies of their implementation in solar cells, light‐emitting diodes, luminescent solar concentrators, and photodetectors.
Carbon dots (CDs) are an attractive class of nanomaterials due to the ease of their synthesis, biocompatibility, and superior optical properties. The electronic structure of CDs and hence their ...optical transitions can be controlled and tuned over a wide spectral range via the choice of precursors, adjustment of the synthetic conditions, and post-synthetic treatment. We summarize recent progress in the synthesis of CDs emitting in different colors in terms of morphology and optical properties of the resulting nanoparticles, with a focus on the synthetic approaches allowing to shift their emission to longer wavelengths. We further consider formation of CD-based composite materials, and review approaches used to prevent aggregation and self-quenching of their emission. We then provide examples of applications of CDs in optoelectronic devices, such as solar cells and light-emitting diodes (LEDs) with a focus on white LEDs.
Carbon dots (CDs) with efficient excitation and emission in deep-red/near-infrared (NIR) spectral range are important for bioimaging applications. Herein, we develop a simple and effective method to ...significantly enhance both the absorption and emission of CDs in deep-red/NIR by suppressing nonradiative charge recombination via deprotonation of the CD surface. As compared to aqueous solutions at room temperature, NIR emission of CDs in
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-dimethylformamide and glycerol experience a 50- and 70-fold increase at -20 °C, respectively, due to enhanced deprotonation ability and viscosity. On the basis of the adjustable NIR fluorescence intensity of CDs, multilevel data encryption in the NIR region is realized by controlling the humidity and the temperature of a CD-ink stamped paper.
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