Optical Properties Of Carbon Dots Research Articles

Luminescent carbon dots encapsulating in Eu3+ doped gahnite spinel nanocomposite for boosting thermal sensing, advanced level III detection and intelligent anti-counterfeiting applications

The exceptional optical properties of carbon dots (CDs) position them as a highly promising category of multifunctional carbon-based nanomaterials. When hydrothermally prepared CDs are incorporated into europium-doped zinc aluminate ZnAl2O4 nanophosphors (ZAO:Eu3+ NPs) synthesized via ultrasonication method, the resulting CDs@ZAO:Eu3+ nanocomposite (NCs) exhibits a broad excitation band, with a prominent peak at approximately 393 nm, perfectly matching the emission wavelength range (500–750 nm) of near-ultraviolet (n-UV) LED chips. Significantly, the CDs (5 wt %)@ZAO:Eu3+ NCs exhibit a remarkable 12.5 folds enhancement in photoluminescence (PL) intensity compared to ZAO:Eu3+ alone, thanks to the Förster Resonance Energy Transfer (FRET) between CDs and Eu3+ ions. This enhancement in luminescence could stem from the CDs capturing electrons and facilitating energy transfer to the luminescent Eu3+ ions. Utilizing CDs to enhance fluorescence presents a straightforward and eco-friendly approach for boosting luminescence properties. Impressively, even under elevated temperatures reaching 420 K, the thermal stability of CDs (5 wt %)@ZAO:Eu3+ NCs remains outstanding, retaining 90 % of its initial luminescence intensity. This highlights its exceptional thermal stability, characterized by a high activation energy of 0.27 eV. With an impressive internal quantum efficiency (IQE) of 87.01 %, the optimized composite also achieves remarkable colour purity (CP), reaching 99.5 %. The relative sensitivity was 1.36 %, at 300 K. Thus, CDs@ZAO:Eu3+ is a promising material for non-contact optical thermometry applications. Utilizing the optimized NCs through a simple powder dusting technique effectively develops latent fingerprints (LFPs) on various surfaces, revealing fingerprints (FPs) under 365 nm UV light. Additionally, the study investigates diverse pore parameters including number, position, size, shape, and inter-spacing. Furthermore, optimized NCs are utilized to create a transparent anti-counterfeiting (AC) ink, offering effective AC features through its red emission under 365 nm UV light.

Investigation of silicon doped carbon dots/Carboxymethyl cellulose gel platform with tunable afterglow and dynamic multistage anticounterfeiting

The remarkable optical properties of carbon dots, particularly their tunable room-temperature phosphorescence, have garnered significant interest. However, challenges such as aggregation propensity and complex phosphorescence control via energy level manipulation during synthesis persist. Addressing these issues, we present a facile gel platform for tunable afterglow materials. This involves chemically cross-linking biomass-derived silicon-doped carbon dots with carboxymethylcellulose and incorporating non-precious metal salts (BaCl2, CaCl2, MgCl2, ZnCl2, ZnBr2, ZnSO4) to enhance phosphorescence. Metal salts boost intersystem crossing via spin–orbit coupling, elevating triplet state transitions and activating phosphorescence. Chemical bonding and salt-induced coordination/electrostatic interactions establish confinement effects, suppressing non-radiative transitions. Diverse salt-gel interactions yield gels with tunable phosphorescence lifetimes (9.48 ms to 32.13–492.39 ms), corresponding to afterglow durations ranging from 3.20 to 11.86 s. With its broad tunability and high recognition, this gel material exhibits promising potential for dynamic multilevel anti-counterfeiting applications.

Formation and Fluorescent Mechanism of Multiple Color Emissive Carbon Dots from o-Phenylenediamine.

Carbon dots (CDs) have received considerable attention in many application areas owing to their unique optical properties and potential applications; however, the fluorescent mechanism is an obstacle to their applications. Herein, three-color emissive CDs are prepared from single o-phenylenediamine (oPD) by regulating the ratio of ethanol and dimethylformamide (DMF). Fluorescent mechanism of these CDs is proposed as molecular state fluorescence. Reaction intermediates are identified using liquid chromatrography-mass spectroscopy (LC-MS) and 1H nuclear magnetic resonance (NMR) spectra. 1H-Benzo[d]imidazole (BI), 2,3-diaminophenazine (DAP), and 5,14-dihydroquinoxalino[2,3-b] phenazine (DHQP) are proposed to be the fluorophores of blue, green, and red emissive CDs by comparing their optical properties. As per the LC-MS and 1H-NMR analysis, DHQP with red emission tends to form from DAP and oPD in pure ethanol. By adding DMF, BI formation is enhanced and DHQP formation is suppressed. The prepared CDs exhibit green emission with DAP. When the DMF amount is >50%, BI formation is considerably promoted, resulting in DAP formation being suppressed. BI with blue emission then turns into the fluorophore of CDs. This result provides us an improved understanding of the fluorescent mechanism of oPD-based CDs, which guides us in designing the structure and optical properties of CDs.

Fluorometric Determination of Fe3+ Ions using Carbon Dots Prepared from the Extract of Singapore Cherry

Background: The development of affordable and ecologically acceptable technologies for heavy metal detection and removal is required due to the rising levels of water and soil pollution. Carbon Dots (CDs) have emerged as a promising nanomaterial for heavy metal detection due to their unique properties. In this study, we report a simple and eco-friendly method to produce CDs using Muntingia calabura fruit extract as a precursor. Methods: The hydrothermal method produced a well-defined size, structure, and optical properties of CDs, which were analyzed by using various characterization techniques, including Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray Spectroscopy (EDS), Elemental mapping (E-map), UV-visible spectroscopy, X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR), Photoluminescence (PL) spectroscopy, and Transmission Electron Microscopy (TEM). Additionally, Zeta potential and DLS analysis were used to characterize the CDs. Results: As-synthesized CDs exhibited strong fluorescence emission, making them suitable for the selective determination of Fe3+ ions. The detection limit was found to be 3.6 μM for Fe3+ ions, which highlighted the potential application of as-prepared CDs in environmental monitoring. Conclusion: The green synthesized CDs from Muntingia calabura fruit extract provided a sustainable approach for developing efficient nanoprobes for detecting Fe3+ ions in environmental and biological samples.

Synthesis and optical properties of luminescent carbon dots from Haloxylon seeds

In this work, local Haloxylon seeds were utilized as a carbon source to synthesize carbon dots (CDs) using the Pyrolysis method. The morphology, structure, and optical properties of CDs were extensively analyzed. The obtained CDs exhibit a spherical shape with an average diameter of 7.7 nm. They are mainly composed of carbon and oxygen, which formed various hydrophilic functional groups on the surface resulting in enhancement of their water solubility. The CDs emit a bright blue fluorescence under excitation wavelength at 320 nm, with an emission peak at 425 nm and a quantum yield of 1.6 %. The emission characteristics of the CDs is a result of the radiative recombination of the carbon-core state and surface defects, which is dependent on the excitation. This research offers an efficient and environmentally-friendly method for synthesizing luminescent CDs from renewable sources.

Fluorine doping induced fluorescence emission redshift of CDs

Elemental doping is an effective way to modify the optical properties of carbon dots (CDs). In this work, the effects of fluorine-doped (F-doped) types and configurations on the structural stability and fluorescence properties of CDs were investigated based on density functional theory and time-dependent density functional theory. Circumcoronene was selected as an undoped structure, and a series of F-doped CD structures including edge and basal plane fluorine-doping (F-doping) types, and CF, CF2 and CF3 configurations were constructed. The calculation results show that the edge CF groups play a more positive role in the structural stability of CDs than the CF2 and basal plane CF groups. Different from the three configurations, the CF3 groups cannot contribute to the structural stability. For optical properties, the edge CF and CF3 groups have less effect on the electron distribution of CDs, hence only a slight fluorescence emission redshift occurs in two F-doping cases. In contrast, the CF2 and basal plane CF groups can evidently influence the highest occupied molecular orbital of the CDs, which induces the charge transfer transition and the fluorescence emission is redshifted to the near-infrared region. This work is helpful to predict the F-doped types and configurations in CDs, reveals the modulation mechanism of F-doping on the fluorescence properties and provides a theoretical guidance for the controlled synthesis of CDs in the future.

Tuning Optical Properties of Carbon Dots by Co‐doping Strategy for Versatile Applications

AbstractCarbon dots (CDs) with tunable photoluminescence was successfully prepared via selective co‐doping of three elements, including nitrogen, phosphorus and sulfur element by green one‐step hydrothermal method. Nitrogen‐sulfur‐doped CDs (red NS‐CDs), which emitted red fluorescence under UV excitation, were used to detect iron ions in the linear range 1–50 μM, yielding detectable limits as low as 94 nM. The nitrogen‐phosphorus‐doped CDs (blue NP‐CDs) exhibited blue fluorescence with quantum yields up to 34.5 %. When the concentration is 800 μg/mL, it showed excellent anticancer effect in vitro. The nitrogen‐sulfur‐phosphorus‐doped CDs (green NPS‐CDs) emitting green fluorescence showed a low cytotoxicity at a high concentration of 800 μg/mL and were used for intracelluar imaging of NCl−H292 cells. This study demonstrated the photoluminescent characteristics of carbon dots (CDs) and highlighted the ability to modify their peak fluorescence emission wavelengths through the flexible combination of specific reagents under comparable hydrothermal conditions. Additionally, it provided valuable insights into the efficient methodologies for synthesizing CDs suitable for various application scenarios.

A multifunctional guanosine-based carbon dots for dead microbial imaging and synergistic broad-spectrum antimicrobial therapy

Pathogenic microbial infection poses serious threats to human lives and antibiotic abuse leads to bacterial resistance. The development of alternative antibacterial agents and strategies with reduced resistance risk is urgently demanded. Heteroatom doping is a feasible method for adjusting the electronic and optical properties of carbon dots (CDs) to improve their bioimaging performance and light-mediated therapeutic efficiency. Herein, we synthesized a series of guanosine-derived CDs from guanosine (G), guanosine monophosphate (GMP), guanosine diphosphate (GDP), and guanosine triphosphate (GTP) as respective precursors. G-CDs, prepared by guanosine with strong surface negative charge and suitable size, can successfully differentiate and stain dead microbial cells (bacteria and fungi). G-CDs with a high N content exhibited the highest antibacterial activity in vitro and in vivo among the four guanosine-derived CDs, owing to triple synergistic antibacterial actions - the intrinsic antibacterial mechanism, bacterial photodynamic and photothermal inactivation against bacteria and fungi. In this paper, we present a promising new method to prepare CDs using natural biomolecules from living systems as precursors for multifunctional dead microbial cells imaging and broad-spectrum theranostic applications.

Localized states in carbon dots: Structural and optical investigation of three systems with varying degrees of carbonization

Carbon dots (CDs) have been widely researched in recent years, mainly to investigate their potential in various applications such as drug delivery, photocatalysis, and sensing. However, understanding of their fundamental properties, including physical and electronic structure, has lagged behind their development in applied sciences. To address this, it is necessary to use novel methods which go beyond the current level of characterization in the literature. In this work, we utilize time of flight-secondary ion mass spectrometry (ToF-SIMS) to generate specific knowledge of the structural components of three CDs generated in our lab. This work revealed that black CDs (B-CDs) possess a highly carbonic structure with nitrogen and oxygen functionalization throughout the particle structure. Carbon nitride dots (CNDs) possess some of these same carbonic structures, but also show the presence of more organic structures which would be expected through a bottom-up approach. In terms of carbonization, CNDs lie between B-CDs and the third sample, yellow-CDs (Y-CDs). Y-CDs are believed to be almost completely polymeric/organic in structure and the groups detected through this mass analysis supports this idea. The structural information from ToF-SIMS is compared with other structural techniques. Additionally, the optical properties of CDs before and after oxidation and reduction are used to craft a proposed photoluminescence (PL) mechanism for each system. The analysis contained herein enables further understanding of the structure of these three samples, and the attained understanding of the surface structure is particularly important for future biomedical applications.

Optical Properties Prediction for Red and Near-Infrared Emitting Carbon Dots Using Machine Learning.

Functional nanostructures build up a basis for the future materials and devices, providing a wide variety of functionalities, a possibility of designing bio-compatible nanoprobes, etc. However, development of new nanostructured materials via trial-and-error approach is obviously limited by laborious efforts on their syntheses, and the cost of materials and manpower. This is one of the reasons for an increasing interest in design and development of novel materials with required properties assisted by machine learning approaches. Here, the dataset on synthetic parameters and optical properties of one important class of light-emitting nanomaterials - carbon dots are collected, processed, and analyzed with optical transitions in the red and near-infrared spectral ranges. A model for prediction of spectral characteristics of these carbon dots based on multiple linear regression is established and verified by comparison of the predicted and experimentally observed optical properties of carbon dots synthesized in three different laboratories. Based on the analysis, the open-source code is provided to be used by researchers for the prediction of optical properties of carbon dots and their synthetic procedures.

Light on multi-mode optical properties of carbon dots through rational surface engineering tuning strategies

Carbon dots (CDs) materials are currently gaining significant attention for applications in bioimaging, fluorescent sensing, anti-counterfeiting, therapeutics, catalysis and other areas. However, efficient and attractive CDs with multi-mode luminescence and tunable spectra through simple modification strategy are still urgently needed for multifunctional optical applications and mechanism exploration. Herein, we demonstrate two rationally designed and completely different CDs surface tuning strategies, which can generate multi-mode optical properties including multi-color fluorescence (FL), room-temperature phosphorescence (RTP) and aggregation-induced emission (AIE). The optical properties after weak interactions modification are characterized by freedom and switchability, while the optical properties after strong interaction modification are characterized by compulsion and non-switchability. Moreover, it is further demonstrated that the cell imaging, light-emitting devices (LEDs), “and” logic gate and anti-counterfeiting applications based on multi-mode optical effects. This study not only provides a new model system for understanding the surface states of CDs, but also opens up opportunities for new applications of multi-mode optical materials for various purposes.

Synthesis of Multicolor Carbon Dots Catalyzed by Inorganic Salts with Tunable Nonlinear Optical Properties.

The nonlinear optical properties of carbon dots have been in the spotlight in recent years. In light of the complexity and diversity of factors affecting the nonlinear optical properties of carbon dots, how to reveal the origin and physical mechanism of the nonlinear optical properties of carbon dots accurately has become a problem. In this work, a template-free method was designed to prepare carbon dots via solid-phase reaction with phloroglucinol as a single carbon source and sodium bisulfate as the catalyst. This method is simple, green, safe, and easy to be prepared on a large scale. Three carbon dots with different luminous colors were obtained by simply adjusting the reaction temperature. The rise of reaction temperature affects the surface functional groups, and then hinders the luminescence of surface states, leading to the change of luminescence properties. The nonlinear optical properties of carbon dots were analyzed by the Z-scan technique. Surprisingly, all carbon dots have nonlinear optical responses, but there are differences in performance. Results prove the increase in sp2 domains may contribute to the significant improvement of the nonlinear optical properties of carbon dots, indicating a direction to improve the nonlinear optical properties of carbon dots.

Nickel doping: Improving the optical properties of carbon dots and increasing the sensitivity for detecting pH and water

pH and water play a crucial role in chemical, environmental and physiological monitoring processes, so it is of great importance to establish a simple and sensitive multi-mode detection method. In this study, we fabricated nickel-doped carbon dots (Ni-CDs) by a hydrothermal method using nickel chloride (NiCl2•6 H2O) and m-phenylenediamine (m-PDA) as precursors, which exhibits excellent photostability, outstanding resistance to photobleaching and ultra-low cytotoxicity. Ni doping increased the fluorescence quantum yield (from 21.4% to 30.3%) and H content (from 44.4% to 57.1%) of the Ni-CDs, making them highly sensitive to pH and water, which facilitated the detection of pH and water based on deprotonation and aggregation mechanisms, respectively. Ni-CDs can detect pH in the ranges of 6.0–9.0 and 6.0–11.0 via fluorometric and smartphone methods, respectively. The limits of detection (LODs) of the Ni-CDs in DMSO, DMF and THF for the detection of water were 0.0112%, 0.0144% and 0.0060%, respectively. Moreover, the Ni-CDs have been effectively utilized for pH detection in real samples as well as for pH in cells and zebrafish with satisfactory results. More importantly, the Ni-CDs/hydrogel remains perfectly the sensitive to pH and water, broadening the applications of the CDs in sensing, bioimaging and information encryption.

Facile preparation, optical mechanism elaboration, and bio-imaging application of fluorescent cellulose nanocrystals with tunable emission wavelength

Interfacing cellulose nanocrystals (CNCs) with fluorescent materials provides more possibilities for constructing of sensory/imaging platforms in biomedical applications. In this work, by harnessing the efficient extraction accompanied modification of CNCs and adjustable optical properties of carbon dots (CDs), we report the constructions and emission wavelength tuning of fluorescent CNCs (F-CNCs) composed of CNC nano-scaffolds and CDs. The as-prepared CNCs are densely decorated with citric acid (CA), which plays the role of carbon source for the in-situ synthesis of CDs on CNCs. For the F-CNCs carrying blue, green, and red emissive CDs, ethylenediamine (EDA), urea, and thiourea are the N or N/S sources. Fingerprints of chemical groups, morphological characters, and redox activities are resolved to elaborate the optical mechanisms of CDs with varying emission colors. The emission wavelength is adjusted by either changing the particle size or introducing new emission centers. Both are primarily achieved via precursor engineering. The F-CNCs reveal quantum yields (QYs) >22 % and negligible fluorescence quenching (< 6 %) upon continuous excitation as long as 24 h. Benefited from their cell membrane penetration capability, the F-CNCs with different emission wavelengths were challenged for multiplexed cytoplasm imaging.

Green synthesis and characterization of carbon dots from Angiopteris evecta (G.Forst.) Hoffm and selective detection of Fe3+ ions

Carbon dots are promising nano materials with wide range of applications. In this work, we have presented a green strategy to prepare fluorescent carbon dots using leaf extracts of Angiopteris evecta by a one-step hydrothermal synthetic strategy. Formation of car bon dots was confirmed by the emission of fluorescence on exposure to UV light source. The optical properties of carbon dots were determined by UV–vis spectrophotometer and Fourier transform-infrared spectroscopy. The carbon dots were found to have many functional groups on their surface. The synthesised CDs were evaluated for their ability to detect metal ions and they exhibited selective detection of Fe3+ ions in aqueous solution.

Synthesis Strategies, Optical Mechanisms, and Applications of Dual-Emissive Carbon Dots.

Tuning the optical properties of carbon dots (CDs) and figuring out the mechanisms underneath the emissive phenomena have been one of the most cutting-edge topics in the development of carbon-based nanomaterials. Dual-emissive CDs possess the intrinsic dual-emission character upon single-wavelength excitation, which significantly benefits their multi-purpose applications. Explosive exploitations of dual-emissive CDs have been reported during the past five years. Nevertheless, there is a lack of a systematic summary of the rising star nanomaterial. In this review, we summarize the synthesis strategies and optical mechanisms of the dual-emissive CDs. The applications in the areas of biosensing, bioimaging, as well as photoelectronic devices are also outlined. The last section presents the main challenges and perspectives in further promoting the development of dual-emissive CDs. By covering the most vital publications, we anticipate that the review is of referential significance for researchers in the synthesis, characterization, and application of dual-emissive CDs.

OPTICAL PROPERTIES OF COLLOIDAL SOLUTIONS OF CARBON DOTS

In this work, optical properties of carbon dots (CDs) chemically synthesized by solvothermal carbonization of a mixture of urea and anhydrous citric acid were studied. Size distribution of CDs with a typical chemical structure was estimated from dynamic light scattering. Absorption, fluorescence excitation/emission spectra as well as characteristic fluorescence lifetimes were measured. An energy diagram of photostimulated electronic transitions in this type of multicolor fluorescent carbon nanoparticles was also proposed. Temperature dependence of the PL/PLE-maps of CDs colloids in the range of 5‒75 ° C was measured and it demonstrates the possibility of their use for thermometry purposes. We also showed a possibility of CDs using for multicolor cell fluorescence imaging.

Optical Properties of Carbon Dots Synthesized by the Hydrothermal Method.

In this study, the optical and structural properties of carbon dots (CDs) synthesized using a hydrothermal method were investigated. CDs were prepared from various precursors such as citric acid (CA), glucose, and birch bark soot. The SEM and AFM results show that the CDs are disc-shaped nanoparticles with dimensions of ~7 nm × 2 nm for CDs from CA, ~11 nm × 4 nm for CDs from glucose, and ~16 nm × 6 nm for CDs from soot. The TEM images of CDs from CA showed stripes with a distance of 0.34 nm between them. We assumed that the CDs synthesized from CA and glucose consisted of graphene nanoplates located perpendicular to the disc plane. The synthesized CDs contain oxygen (hydroxyl, carboxyl, carbonyl) and nitrogen (amino, nitro) functional groups. CDs have strong absorption in the ultraviolet region in the range of 200-300 nm. All CDs synthesized from different precursors displayed bright luminescence in the blue-green region of the spectrum (420-565 nm). We found that the luminescence of CDs depended on the synthesis time and type of precursors. The results show that the radiative transitions of electrons occur from two levels with energies ~3.0 eV and ~2.6 eV, which are due to the presence of functional groups.

Carbon dots preserve strong blue emission in both aqueous and solid states and their application in intracellular temperature sensing and white light-emitting diodes

The emission of carbon dots is usually quenched in the solid state, thus limiting their application. Herein, we reported the structure and optical properties of carbon dots that preserve intense blue emission in both aqueous and solid states. Structural analysis indicates the obtained carbon dots are largely functionalized by sodium ion (Na+), which could keep the carbon core from direct contact and inhibit the fluorescence resonance energy transfer, leading the carbon dots still emit even after drying to solid powder. Moreover, in addition to the emission intensity, the luminescence lifetime of the aqueous carbon dots responds linearly to temperature in the physiological temperature range from 20 to 70 °C, and is stable at different pH and salinity environments, making them promising optical nanothermometers for probing intracellular temperature via dual mode (emission intensity/lifetime). The applicability of the aqueous carbon dots for intracellular temperature sensing has been demonstrated in living cell studies, while that for the solid carbon dots has been demonstrated by constructing a prototype white LEDs with high color rendering index of 95.

Exploring the Impact of Nitrogen Doping on the Optical Properties of Carbon Dots Synthesized from Citric Acid.

The differences between bare carbon dots (CDs) and nitrogen-doped CDs synthesized from citric acid as a precursor are investigated, aiming at understanding the mechanisms of emission and the role of the doping atoms in shaping the optical properties. Despite their appealing emissive features, the origin of the peculiar excitation-dependent luminescence in doped CDs is still debated and intensively being examined. This study focuses on the identification of intrinsic and extrinsic emissive centers by using a multi-technique experimental approach and computational chemistry simulations. As compared to bare CDs, nitrogen doping causes the decrease in the relative content of O-containing functional groups and the formation of both N-related molecular and surface centers that enhance the quantum yield of the material. The optical analysis suggests that the main emission in undoped nanoparticles comes from low-efficient blue centers bonded to the carbogenic core, eventually with surface-attached carbonyl groups, the contribution in the green range being possibly related to larger aromatic domains. On the other hand, the emission features of N-doped CDs are mainly due to the presence of N-related molecules, with the computed absorption transitions calling for imidic rings fused to the carbogenic core as the potential structures for the emission in the green range.