The Experts below are selected from a list of 17964 Experts worldwide ranked by ideXlab platform
Andrey L Rogach - One of the best experts on this subject based on the ideXlab platform.
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tracking the source of Carbon Dot photoluminescence aromatic domains versus molecular fluorophores
Nano Letters, 2017Co-Authors: Florian Ehrat, Andrey L Rogach, Santanu Bhattacharyya, Julian Schneider, Achim Lof, Regina Wyrwich, Jacek K Stolarczyk, Alexander S Urban, Jochen FeldmannAbstract:Carbon Dots (CDs) are an intriguing fluorescent material; however, due to a plethora of synthesis techniques and precursor materials, there is still significant debate on their structure and the origin of their optical properties. The two most prevalent mechanisms to explain them are based on polycyclic aromatic hydroCarbon domains and small molecular fluorophores, for instance, citrazinic acid. Yet, how these form and whether they can exist simultaneously is still under study. To address this, we vary the hydrothermal synthesis time of CDs obtained from citric acid and ethylenediamine and show that in the initial phase molecular fluorophores, likely 2-pyridone derivatives, account for the blue luminescence of the Dots. However, over time, while the overall size of the CDs does not change, aromatic domains form and grow, resulting in a second, faster decay channel at similar wavelengths and also creating additional lower energetic states. Electrophoresis provides further evidence that the ensemble of CDs ...
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full color inorganic Carbon Dot phosphors for white light emitting diodes
Advanced Optical Materials, 2017Co-Authors: Zhen Tian, Radek Zboril, Xutao Zhang, Ding Zhou, Pengtao Jing, Dezhen Shen, Andrey L RogachAbstract:Light-emitting Carbon Dots (CDots) are widely investigated due to their distinct merits. However, it is still a challenge to modulate their bandgap emissions and conquer their aggregation-induced luminescence quenching to achieve full-color highly emissive CDot-based phosphors. Herein, this study proposes an approach toward realization of full-color emissive CDots from two common precursors, citric acid and urea, through employing three different solvents (water, glycerol, and dimethylformamide) and their combinations in a solvothermal synthesis. Employing sodium silicate solution, this study further demonstrates the microwave-assisted method allowing to incorporate CDots into a silica network, which effectively prevents aggregation of CDots and results in strongly luminescent full-color inorganic CDot phosphors with photoluminescence quantum yields of 30–40%. Through deposition of the red- and green-emitting CDot phosphors on blue-emitting InGaN chips, white-light-emitting diodes are fabricated with Commission Internationale de L'Eclairage of (0.34, 0.31) and the color rendering index of 82.4, indicating their promising application for solid-state lighting.
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Carbon Dot nanothermometry intracellular photoluminescence lifetime thermal sensing
ACS Nano, 2017Co-Authors: Sergii Kalytchuk, Yu Wang, Kateřina Polakova, Jens P Froning, Klara Cepe, Andrey L Rogach, Radek ZbořilAbstract:Nanoscale biocompatible photoluminescence (PL) thermometers that can be used to accurately and reliably monitor intracellular temperatures have many potential applications in biology and medicine. Ideally, such nanothermometers should be functional at physiological pH across a wide range of ionic strengths, probe concentrations, and local environments. Here, we show that water-soluble N,S-co-doped Carbon Dots (CDs) exhibit temperature-dependent photoluminescence lifetimes and can serve as highly sensitive and reliable intracellular nanothermometers. PL intensity measurements indicate that these CDs have many advantages over alternative semiconductor- and CD-based nanoscale temperature sensors. Importantly, their PL lifetimes remain constant over wide ranges of pH values (5–12), CD concentrations (1.5 × 10–5 to 0.5 mg/mL), and environmental ionic strengths (up to 0.7 mol·L–1 NaCl). Moreover, they are biocompatible and nontoxic, as demonstrated by cell viability and flow cytometry analyses using NIH/3T3 and...
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Molecular Fluorescence in Citric Acid-Based Carbon Dots
The Journal of Physical Chemistry C, 2017Co-Authors: Julian Schneider, Claas J Reckmeier, Yuan Xiong, Maximilian Von Seckendorff, Andrei S. Susha, Peter Kasak, Andrey L RogachAbstract:Nitrogen-doped Carbon Dots synthesized from citric acid as a Carbon precursor have recently been considered to contain fluorescent derivatives of citrazinic acid, which contribute to their emission in the blue spectral range. To study the impact of such molecular fluorescent species on the optical properties of Carbon Dots, we synthesized three samples employing citric acid and three different nitrogen sources: ethylenediamine, hexamethylenetetramine, and triethanolamine. On the basis of the analysis of the nitrogen content and its coordination by X-ray photoelectron spectroscopy, FTIR spectra, and systematically comparing absorption, steady-state emission, and photoluminescence decays of each kind of Carbon Dot, we derive the influence of the molecular precursors and gain further understanding of the complex structure of Carbon Dots highlighting the strong impact of molecular fluorescence in the samples produced with ethylenediamine and hexamethylenetetramine.
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combination of Carbon Dot and polymer Dot phosphors for white light emitting diodes
Nanoscale, 2015Co-Authors: Chun Sun, Yu Zhang, Xiaoyu Zhang, Tieqiang Zhang, Jun Zhao, Kai Sun, Claas J Reckmeier, Andrey L RogachAbstract:We realized white light-emitting diodes with high color rendering index (85–96) and widely variable color temperatures (2805–7786 K) by combining three phosphors based on Carbon Dots and polymer Dots, whose solid-state photoluminescence self-quenching was efficiently suppressed within a polyvinyl pyrrolidone matrix. All three phosphors exhibited dominant absorption in the UV spectral region, which ensured the weak reabsorption and no energy transfer crosstalk. The WLEDs showed excellent color stability against the increasing current because of the similar response of the tricolor phosphors to the UV light variation.
Yu Wang - One of the best experts on this subject based on the ideXlab platform.
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Carbon Dot nanothermometry intracellular photoluminescence lifetime thermal sensing
ACS Nano, 2017Co-Authors: Sergii Kalytchuk, Yu Wang, Kateřina Polakova, Jens P Froning, Klara Cepe, Andrey L Rogach, Radek ZbořilAbstract:Nanoscale biocompatible photoluminescence (PL) thermometers that can be used to accurately and reliably monitor intracellular temperatures have many potential applications in biology and medicine. Ideally, such nanothermometers should be functional at physiological pH across a wide range of ionic strengths, probe concentrations, and local environments. Here, we show that water-soluble N,S-co-doped Carbon Dots (CDs) exhibit temperature-dependent photoluminescence lifetimes and can serve as highly sensitive and reliable intracellular nanothermometers. PL intensity measurements indicate that these CDs have many advantages over alternative semiconductor- and CD-based nanoscale temperature sensors. Importantly, their PL lifetimes remain constant over wide ranges of pH values (5–12), CD concentrations (1.5 × 10–5 to 0.5 mg/mL), and environmental ionic strengths (up to 0.7 mol·L–1 NaCl). Moreover, they are biocompatible and nontoxic, as demonstrated by cell viability and flow cytometry analyses using NIH/3T3 and...
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Carbon Dot hybrids with oligomeric silsesquioxane solid state luminophores with high photoluminescence quantum yield and applicability in white light emitting devices
Chemical Communications, 2015Co-Authors: Yu Wang, Radek Zboril, Sergii Kalytchuk, Lingyun Wang, Klara Cepe, Olga Zhovtiuk, Andrey L RogachAbstract:We present a simple approach towards highly efficient solid-state luminophores with strong deep blue emission and a record high photoluminescence quantum yield of 60% by embedding water-soluble N,S-co-doped Carbon Dots into a polyhedral oligomeric silsesquioxane (POSS) matrix.
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Carbon Dots emerging light emitters for bioimaging cancer therapy and optoelectronics
Nano Today, 2014Co-Authors: Katerina Hola, Radek Zboril, Emmanuel P Giannelis, Yu Wang, Yu Zhang, Andrey L A.l. Andrey L RogachAbstract:Abstract Carbon Dots represent an emerging class of fluorescent materials and provide a broad application potential in various fields of biomedicine and optoelectronics. In this review, we introduce various synthetic strategies and basic photoluminescence properties of Carbon Dots, and then address their advanced in vitro and in vivo bioapplications including cell imaging, photoacoustic imaging, photodynamic therapy and targeted drug delivery. We further consider the applicability of Carbon Dots as components of light emitting diodes, which include Carbon Dot based electroluminescence, optical down-conversion, and hybrid plasmonic devices. The review concludes with an outlook towards future developments of these emerging light-emitting materials.
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thickness dependent full color emission tunability in a flexible Carbon Dot ionogel
Journal of Physical Chemistry Letters, 2014Co-Authors: Yu Wang, Yu Zhang, Sergii Kalytchuk, Stephen V Kershaw, Hengchong Shi, Andrey L RogachAbstract:Multicolor luminescent materials are of immense importance nowadays, while it still constitutes a challenge to achieve luminescence color tunability, transparency, and flexibility at the same time. Here we show how ultrasmall Carbon Dots (CDs) fluorescing strongly across the visible spectrum can be surface functionalized and incorporated into highly flexible hybrid materials by combination with ionic liquids within silica gel networks to form CD-ionogels with properties promising for fabrication of flexible displays and other optical technologies without the use of any toxic materials. We demonstrate how the emission from such hybrid materials can be tuned across a large range of the Commission Internationale de l'Enclairage (CIE) display gamut giving full-color performance. We highlight how the rich ladder of emissive states attributable to organic functional groups and CD surface functionalization supports a smooth sequential multiple self-absorption tuning mechanism to red shift continuously from blue emitting n-π* transitions down through the lower energy states.
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color switchable electroluminescence of Carbon Dot light emitting diodes
ACS Nano, 2013Co-Authors: Xiaoyu Zhang, Yu Wang, Yu Zhang, Sergii Kalytchuk, Stephen V Kershaw, Yinghui Wang, Peng Wang, Tieqiang Zhang, Yi Zhao, Hanzhuang ZhangAbstract:Carbon-Dot based light-emitting diodes (LEDs) with driving current controlled color change are reported. These devices consist of a Carbon-Dot emissive layer sandwiched between an organic hole transport layer and an organic or inorganic electron transport layer fabricated by a solution-based process. By tuning the device structure and the injecting current density (by changing the applied voltage), we can obtain multicolor emission of blue, cyan, magenta, and white from the same Carbon Dots. Such a switchable EL behavior with white emission has not been observed thus far in single emitting layer structured nanomaterial LEDs. This interesting current density-dependent emission is useful for the development of colorful LEDs. The pure blue and white emissions are obtained by tuning the electron transport layer materials and the thickness of electrode.
Yu Zhang - One of the best experts on this subject based on the ideXlab platform.
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combination of Carbon Dot and polymer Dot phosphors for white light emitting diodes
Nanoscale, 2015Co-Authors: Chun Sun, Yu Zhang, Xiaoyu Zhang, Tieqiang Zhang, Jun Zhao, Kai Sun, Claas J Reckmeier, Andrey L RogachAbstract:We realized white light-emitting diodes with high color rendering index (85–96) and widely variable color temperatures (2805–7786 K) by combining three phosphors based on Carbon Dots and polymer Dots, whose solid-state photoluminescence self-quenching was efficiently suppressed within a polyvinyl pyrrolidone matrix. All three phosphors exhibited dominant absorption in the UV spectral region, which ensured the weak reabsorption and no energy transfer crosstalk. The WLEDs showed excellent color stability against the increasing current because of the similar response of the tricolor phosphors to the UV light variation.
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Carbon Dots emerging light emitters for bioimaging cancer therapy and optoelectronics
Nano Today, 2014Co-Authors: Katerina Hola, Radek Zboril, Emmanuel P Giannelis, Yu Wang, Yu Zhang, Andrey L A.l. Andrey L RogachAbstract:Abstract Carbon Dots represent an emerging class of fluorescent materials and provide a broad application potential in various fields of biomedicine and optoelectronics. In this review, we introduce various synthetic strategies and basic photoluminescence properties of Carbon Dots, and then address their advanced in vitro and in vivo bioapplications including cell imaging, photoacoustic imaging, photodynamic therapy and targeted drug delivery. We further consider the applicability of Carbon Dots as components of light emitting diodes, which include Carbon Dot based electroluminescence, optical down-conversion, and hybrid plasmonic devices. The review concludes with an outlook towards future developments of these emerging light-emitting materials.
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thickness dependent full color emission tunability in a flexible Carbon Dot ionogel
Journal of Physical Chemistry Letters, 2014Co-Authors: Yu Wang, Yu Zhang, Sergii Kalytchuk, Stephen V Kershaw, Hengchong Shi, Andrey L RogachAbstract:Multicolor luminescent materials are of immense importance nowadays, while it still constitutes a challenge to achieve luminescence color tunability, transparency, and flexibility at the same time. Here we show how ultrasmall Carbon Dots (CDs) fluorescing strongly across the visible spectrum can be surface functionalized and incorporated into highly flexible hybrid materials by combination with ionic liquids within silica gel networks to form CD-ionogels with properties promising for fabrication of flexible displays and other optical technologies without the use of any toxic materials. We demonstrate how the emission from such hybrid materials can be tuned across a large range of the Commission Internationale de l'Enclairage (CIE) display gamut giving full-color performance. We highlight how the rich ladder of emissive states attributable to organic functional groups and CD surface functionalization supports a smooth sequential multiple self-absorption tuning mechanism to red shift continuously from blue emitting n-π* transitions down through the lower energy states.
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color switchable electroluminescence of Carbon Dot light emitting diodes
ACS Nano, 2013Co-Authors: Xiaoyu Zhang, Yu Wang, Yu Zhang, Sergii Kalytchuk, Stephen V Kershaw, Yinghui Wang, Peng Wang, Tieqiang Zhang, Yi Zhao, Hanzhuang ZhangAbstract:Carbon-Dot based light-emitting diodes (LEDs) with driving current controlled color change are reported. These devices consist of a Carbon-Dot emissive layer sandwiched between an organic hole transport layer and an organic or inorganic electron transport layer fabricated by a solution-based process. By tuning the device structure and the injecting current density (by changing the applied voltage), we can obtain multicolor emission of blue, cyan, magenta, and white from the same Carbon Dots. Such a switchable EL behavior with white emission has not been observed thus far in single emitting layer structured nanomaterial LEDs. This interesting current density-dependent emission is useful for the development of colorful LEDs. The pure blue and white emissions are obtained by tuning the electron transport layer materials and the thickness of electrode.
Fraser J Stoddart - One of the best experts on this subject based on the ideXlab platform.
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in situ photoconversion of multicolor luminescence and pure white light emission based on Carbon Dot supported supramolecular assembly
Journal of the American Chemical Society, 2019Co-Authors: Huang Wu, Peiyu Li, Fraser J Stoddart, Yong ChenAbstract:Constructing multicolor photoluminescence materials that allow for the integration of suitable external stimuli in order to control luminescence color conversions is a challenging objective. Multicolor luminescent output that is regulated in an in situ photo-controlled manner is not a common phenomenon. Herein, a photoluminescent supramolecular assembly, prepared in two stages, is described that displays in situ photo-tuning broad-spectrum output. Benefiting from the reversible photo-switched constitutional interconversion of diarylethenes, the fluorescence of a guest molecule, styrylpyridinium-modified diarylethene, can be switched on/off by alternating ultraviolet and visible light irradiation. Upon complexation of this guest with a host, cucurbit[8]uril, the fluorescence intensity of the resulting binary supramolecular nanofiber shows a drastic enhancement when compared with that of the free guest, which can also be quenched and recovered reversibly by light irradiation. Significantly, such cationic su...
Radek Zboril - One of the best experts on this subject based on the ideXlab platform.
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full color inorganic Carbon Dot phosphors for white light emitting diodes
Advanced Optical Materials, 2017Co-Authors: Zhen Tian, Radek Zboril, Xutao Zhang, Ding Zhou, Pengtao Jing, Dezhen Shen, Andrey L RogachAbstract:Light-emitting Carbon Dots (CDots) are widely investigated due to their distinct merits. However, it is still a challenge to modulate their bandgap emissions and conquer their aggregation-induced luminescence quenching to achieve full-color highly emissive CDot-based phosphors. Herein, this study proposes an approach toward realization of full-color emissive CDots from two common precursors, citric acid and urea, through employing three different solvents (water, glycerol, and dimethylformamide) and their combinations in a solvothermal synthesis. Employing sodium silicate solution, this study further demonstrates the microwave-assisted method allowing to incorporate CDots into a silica network, which effectively prevents aggregation of CDots and results in strongly luminescent full-color inorganic CDot phosphors with photoluminescence quantum yields of 30–40%. Through deposition of the red- and green-emitting CDot phosphors on blue-emitting InGaN chips, white-light-emitting diodes are fabricated with Commission Internationale de L'Eclairage of (0.34, 0.31) and the color rendering index of 82.4, indicating their promising application for solid-state lighting.
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Carbon Dot hybrids with oligomeric silsesquioxane solid state luminophores with high photoluminescence quantum yield and applicability in white light emitting devices
Chemical Communications, 2015Co-Authors: Yu Wang, Radek Zboril, Sergii Kalytchuk, Lingyun Wang, Klara Cepe, Olga Zhovtiuk, Andrey L RogachAbstract:We present a simple approach towards highly efficient solid-state luminophores with strong deep blue emission and a record high photoluminescence quantum yield of 60% by embedding water-soluble N,S-co-doped Carbon Dots into a polyhedral oligomeric silsesquioxane (POSS) matrix.
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Carbon Dots emerging light emitters for bioimaging cancer therapy and optoelectronics
Nano Today, 2014Co-Authors: Katerina Hola, Radek Zboril, Emmanuel P Giannelis, Yu Wang, Yu Zhang, Andrey L A.l. Andrey L RogachAbstract:Abstract Carbon Dots represent an emerging class of fluorescent materials and provide a broad application potential in various fields of biomedicine and optoelectronics. In this review, we introduce various synthetic strategies and basic photoluminescence properties of Carbon Dots, and then address their advanced in vitro and in vivo bioapplications including cell imaging, photoacoustic imaging, photodynamic therapy and targeted drug delivery. We further consider the applicability of Carbon Dots as components of light emitting diodes, which include Carbon Dot based electroluminescence, optical down-conversion, and hybrid plasmonic devices. The review concludes with an outlook towards future developments of these emerging light-emitting materials.