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Xiaogang Liu

Bio: Xiaogang Liu is an academic researcher from National University of Singapore. The author has contributed to research in topics: Medicine & Photon upconversion. The author has an hindex of 94, co-authored 425 publications receiving 41825 citations. Previous affiliations of Xiaogang Liu include Heilongjiang University & Massachusetts Institute of Technology.


Papers
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TL;DR: In this article, the ultraviolet-visible absorption and fluorescence spectra of coumarin 3 carboxylic acid (1) were investigated in three representative solvents: cyclohexane, ethanol, and dimethyl sulfoxide (DMSO).
Abstract: 7-(Diethylamino)-coumarin-3-carboxylic acid (1) has been used as a laser dye, fluorescent label, and biomedical inhibitor in many different applications. Although this dye is typically used in the solution phase, it is prone to molecular aggregation, resulting in many inconsistent optoelectronic properties being reported in the literature. In this paper, the ultraviolet–visible absorption and fluorescence spectra of 1 are investigated in three representative solvents: cyclohexane [nonpolar and non-hydrogen bonding (NHB)], ethanol (moderately polar and hydrogen bond accepting and donating), and dimethyl sulfoxide (DMSO) (strongly polar and hydrogen bond accepting). These experimental results, in conjunction with (time-dependent) density functional theory (DFT/TD-DFT)-based quantum calculations, have led to the identification of the J-aggregates of 1 and rationalized its different aggregation characteristic in cyclohexane in contrast to that of another similar compound, coumarin 343. We show here that these...

30 citations

Journal ArticleDOI
TL;DR: In this paper, the 9,10-diphenylanthracene (9, 10-DPA) single crystals are used as a representative model, which are grown via low-temperature solution processes, exhibiting intense X-ray radioluminescence with ultrahigh photon-conversion efficiency, ultrafast response and high sensitivity.
Abstract: Low-dose, high-resolution X-ray imaging is vital for medical diagnostics and material/device analyses. Current X-ray imagers are dominated by expensive inorganic materials via high-temperature solid processes (up to 1700 °C, e.g., CsI:Tl) with heavy metal elements. It is essential to search for new materials as X-ray imagers with low growth temperature, low cost, high sensitivity, along with high chemical and environmental stability. Here, 9,10-diphenylanthracene (9,10-DPA) single crystals are used as a representative model, which are grown via low-temperature solution processes, exhibiting intense X-ray radioluminescence with ultrahigh photon-conversion efficiency, ultrafast response and high sensitivity. The resolution of devices based on organic crystals exceeds 20.00 lp mm-1 . Meanwhile the crystals exhibit high cycle performance under X-ray irradiation and environmental stability. This study demonstrates that organic semiconductors have potential use in low-cost, high-sensitivity and low-dose X-ray imaging systems.

29 citations

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate photon upconversion of diverse lanthanide emitters by harnessing triplet exciton-mediated energy relay, which is less dependent on excitation power and enhances the emission intensity of Tb3+ by 158 times.
Abstract: Exploration of upconversion luminescence from lanthanide emitters through energy migration has profound implications for fundamental research and technology development. However, energy migration-mediated upconversion requires stringent experimental conditions, such as high power excitation and special migratory ions in the host lattice, imposing selection constraints on lanthanide emitters. Here we demonstrate photon upconversion of diverse lanthanide emitters by harnessing triplet exciton-mediated energy relay. Compared with gadolinium-based systems, this energy relay is less dependent on excitation power and enhances the emission intensity of Tb3+ by 158-fold. Mechanistic investigations reveal that emission enhancement is attributable to strong coupling between lanthanides and surface molecules, which enables fast triplet generation (<100 ps) and subsequent near-unity triplet transfer efficiency from surface ligands to lanthanides. Moreover, the energy relay approach supports long-distance energy transfer and allows upconversion modulation in microstructures. These findings enhance fundamental understanding of energy transfer at molecule-nanoparticle interfaces and open exciting avenues for developing hybrid, high-performance optical materials. Photon upconversion in lanthanide-doped nanoparticles enables important technological developments. Here the authors demonstrate a mechanism leading to enhanced upconversion emission in core-shell nanoparticles, and long-distance energy transfer between nanoparticles, through triplet state population of an organic surface ligand.

29 citations

Journal ArticleDOI
TL;DR: In this paper, the authors report 9 metal organic frameworks constructed with various combinations of the following ligands: trans,trans-9,10-bis(4-pyridylethenyl) anthracene.
Abstract: The development of alternative nonlinear optical metamaterials has attracted much attention recently due to technological demands. Upconversion emission via a simultaneous two-photon absorption process is a nonlinear process that is widely studied in synthetically challenging organic compounds. Hereby, we report 9 metal organic frameworks constructed with various combinations of the following ligands: trans,trans-9,10-bis(4-pyridylethenyl) anthracene, trans,trans-9,10-bis(4-pyridylethynyl) anthracene, 1,4-bis[2-(4′-pyridyl)ethenyl]benzene, 4,4′-stilbene dicarboxylate, 4,4′-biphenyl dicarboxylate, 4,4′-benzene dicarboxylate, and benzene-1,3,5-tricarboxylate. Altering the auxiliary carboxylate ligands not only changes the structure but also varies the two-photon excited fluorescence. The two-photon excited emission is enhanced when longer spacer ligands are used and when they are packed in more expanded structures in hms topology. Unusually, the emission becomes stronger when a pair of pyridyl type ligands ...

29 citations

Journal ArticleDOI
TL;DR: In this paper, the authors report close proximity tetrazine-dye conjugates with minimal distance between tetrazines and the fluorophore, and demonstrate their potential for live cell imaging in combination with unnatural amino acids, wash-free multicolor and super-resolution STED, and SOFI imaging.
Abstract: Small-molecule fluorophores enable the observation of biomolecules in their native context with fluorescence microscopy. Specific labeling via bio-orthogonal tetrazine chemistry combines minimal label size with rapid labeling kinetics. At the same time, fluorogenic tetrazine-dye conjugates exhibit efficient quenching of dyes prior to target binding. However, live-cell compatible long-wavelength fluorophores with strong fluorogenicity have been difficult to realize. Here, we report close proximity tetrazine-dye conjugates with minimal distance between tetrazine and the fluorophore. Two synthetic routes give access to a series of cell-permeable and -impermeable dyes including highly fluorogenic far-red emitting derivatives with electron exchange as the dominant excited-state quenching mechanism. We demonstrate their potential for live-cell imaging in combination with unnatural amino acids, wash-free multicolor and super-resolution STED, and SOFI imaging. These dyes pave the way for advanced fluorescence imaging of biomolecules with minimal label size.

29 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
08 Jun 2001-Science
TL;DR: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated and self-organized, <0001> oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process.
Abstract: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 03 nanometer The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis

8,592 citations

Journal ArticleDOI
TL;DR: Physical structure is known to contribute to the appearance of bird plumage through structural color and specular reflection, but a third mechanism, structural absorption, leads to low reflectance and super black color in birds of paradise feathers.
Abstract: Many studies have shown how pigments and internal nanostructures generate color in nature. External surface structures can also influence appearance, such as by causing multiple scattering of light (structural absorption) to produce a velvety, super black appearance. Here we show that feathers from five species of birds of paradise (Aves: Paradisaeidae) structurally absorb incident light to produce extremely low-reflectance, super black plumages. Directional reflectance of these feathers (0.05-0.31%) approaches that of man-made ultra-absorbent materials. SEM, nano-CT, and ray-tracing simulations show that super black feathers have titled arrays of highly modified barbules, which cause more multiple scattering, resulting in more structural absorption, than normal black feathers. Super black feathers have an extreme directional reflectance bias and appear darkest when viewed from the distal direction. We hypothesize that structurally absorbing, super black plumage evolved through sensory bias to enhance the perceived brilliance of adjacent color patches during courtship display.

5,916 citations