Showing papers by "Xiaogang Liu published in 2014"
TL;DR: An overview of recent development in metal-organic complexes with controlled molecular structures and tunable properties is presented, including advances in extending the control of molecular structures to solid materials for energy conversion and information technology applications.
Abstract: The design and characterization of metal–organic complexes for optoelectronic applications is an active area of research. The metal–organic complex offers unique optical and electronic properties arising from the interplay between the inorganic metal and the organic ligand. The ability to modify chemical structure through control over metal–ligand interaction on a molecular level could directly impact the properties of the complex. When deposited in thin film form, this class of materials enable the fabrication of a wide variety of low-cost electronic and optoelectronic devices. These include light emitting diodes, solar cells, photodetectors, field-effect transistors as well as chemical and biological sensors. Here we present an overview of recent development in metal–organic complexes with controlled molecular structures and tunable properties. Advances in extending the control of molecular structures to solid materials for energy conversion and information technology applications will be highlighted.
946 citations
TL;DR: This protocol describes the detailed experimental procedure for synthesizing core-shell NaGdF4 nanoparticles that incorporate lanthanide ions into different layers for efficiently converting a single-wavelength, near-IR excitation into a tunable visible emission.
Abstract: Sodium gadolinium fluoride (NaGdF4) is an ideal host material for the incorporation of luminescent lanthanide ions because of its high photochemical stability, low vibrational energy and its ability to mediate energy exchanges between the lanthanide dopants This protocol describes the detailed experimental procedure for synthesizing core-shell NaGdF4 nanoparticles that incorporate lanthanide ions into different layers for efficiently converting a single-wavelength, near-IR excitation into a tunable visible emission These nanoparticles can then be used as luminescent probes in biological samples, in 3D displays, in solar energy conversion and in photodynamic therapy The NaGdF4 nanoparticles are grown through co-precipitation in a binary solvent mixture of oleic acid and 1-octadecene Doping by lanthanides with controlled compositions and concentrations can be achieved concomitantly with particle growth The lanthanide-doped NaGdF4 nanoparticles then serve as seed crystals for subsequent epitaxial growth of shell layers comprising different lanthanide dopants The entire procedure for the preparation and isolation of the core-shell nanoparticles comprising two epitaxial shell layers requires ∼15 h for completion
485 citations
TL;DR: A new class of upconversion nanocrystals adopting an orthorhombic crystallographic structure in which the lanthanide ions are distributed in arrays of tetrad clusters is described, which enables the preservation of excitation energy within the sublattice domain and effectively minimizes the migration ofexcitation energy to defects.
Abstract: Lanthanide-doped nanocrystals can be used to upconvert infrared radiation into visible light, and are thought to be promising for a range of photonic and biological imaging applications. It is now shown that the upconversion efficiency can be improved by appropriately clustering the lanthanide ions on different structural sublattices.
482 citations
TL;DR: The underlying principles of controlling energy transfer through lanthanide doping are presented, the major advances and key challenging issues in improving upconversion luminescence are overviewed, and the likely directions of future research in the field are considered.
Abstract: The enthusiasm for research on lanthanide-doped upconversion nanoparticles is driven by both a fundamental interest in the optical properties of lanthanides embedded in different host lattices and their promise for broad applications ranging from biological imaging to photodynamic therapy. Despite the considerable progress made in the past decade, the field of upconversion nanoparticles has been hindered by significant experimental challenges associated with low upconversion conversion efficiencies. Recent experimental and theoretical studies on upconversion nanoparticles have, however, led to the development of several effective approaches to enhancing upconversion luminescence, which could have profound implications for a range of applications. Herein we present the underlying principles of controlling energy transfer through lanthanide doping, overview the major advances and key challenging issues in improving upconversion luminescence, and consider the likely directions of future research in the field.
463 citations
TL;DR: In this article, the use of black silicon (BSi) as an anti-reflection coating in solar cells is examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules.
Abstract: Black silicon (BSi) represents a very active research area in renewable energy materials. The rise of BSi as a focus of study for its fundamental properties and potentially lucrative practical applications is shown by several recent results ranging from solar cells and light-emitting devices to antibacterial coatings and gas-sensors. In this paper, the common BSi fabrication techniques are first reviewed, including electrochemical HF etching, stain etching, metal-assisted chemical etching, reactive ion etching, laser irradiation and the molten salt Fray-Farthing-Chen-Cambridge (FFC-Cambridge) process. The utilization of BSi as an anti-reflection coating in solar cells is then critically examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules. Methods of incorporating BSi in advanced solar cell architectures and the production of ultra-thin and flexible BSi wafers are also surveyed. Particular attention is given to routes leading to passivated BSi surfaces, which are essential for improving the electrical properties of any devices incorporating BSi, with a special focus on atomic layer deposition of Al2O3. Finally, three potential research directions worth exploring for practical solar cell applications are highlighted, namely, encapsulation effects, the development of micro-nano dual-scale BSi, and the incorporation of BSi into thin solar cells. It is intended that this paper will serve as a useful introduction to this novel material and its properties, and provide a general overview of recent progress in research currently being undertaken for renewable energy applications.
397 citations
TL;DR: This work designs and fabricates nanoparticles displaying tailorable optical properties and demonstrates that an inert-shell coating provides the particles with stable emission against perturbation in surrounding environments, paving the way for their applications in the context of biological networks.
Abstract: ConspectusLanthanide-doped nanoparticles exhibit unique luminescent properties, including large Stokes shift, sharp emission bandwidth, high resistance to optical blinking, and photobleaching, as well as the unique ability to convert long-wavelength stimulation into short-wavelength emission. These attributes are particularly needed for developing luminescent labels as alternatives to organic fluorophores and quantum dots. In recent years, the well-recognized advantages of upconversion nanocrystals as biomarkers have been manifested in many important applications, such as highly sensitive molecular detection and autofluorescence-free cell imaging. However, their potential in multiplexed detection and multicolor imaging is rarely exploited, largely owing to the research lagging on multicolor tuning of these particles.Lanthanide doping typically involves an insulating host matrix and a trace amount of lanthanide dopants embedded in the host lattice. The luminescence observed from these doped crystalline mat...
383 citations
TL;DR: This work reports the synthesis of luminescent crystals based on hexagonal-phase NaYF4 upconversion microrods and demonstrates that these novel materials offer opportunities as optical barcodes for anticounterfeiting and multiplexed labeling applications.
Abstract: We report the synthesis of luminescent crystals based on hexagonal-phase NaYF4 upconversion microrods. The synthetic procedure involves an epitaxial end-on growth of upconversion nanocrystals comprising different lanthanide activators onto the NaYF4 microrods. This bottom-up method readily affords multicolor-banded crystals in gram quantity by varying the composition of the activators. Importantly, the end-on growth method using one-dimensional microrods as the template enables facile multicolor tuning in a single crystal, which is inaccessible in conventional upconversion nanoparticles. We demonstrate that these novel materials offer opportunities as optical barcodes for anticounterfeiting and multiplexed labeling applications.
325 citations
TL;DR: This review attempts to elucidate the fundamental physical principles that govern the energy conversion by the upconversion materials, and provides a useful guide to materials synthesis and optoelectronic device fabrication based on lanthanide-doped upconverted materials.
Abstract: Photovoltaics and photocatalysis are two significant applications of clean and sustainable solar energy, albeit constrained by their inability to harvest the infrared spectrum of solar radiation. Lanthanide-doped materials are particularly promising in this regard, with tunable absorption in the infrared region and the ability to convert the long-wavelength excitation into shorter-wavelength light output through an upconversion process. In this review, we highlight the emerging applications of lanthanide-doped upconversion materials in the areas of photovoltaics and photocatalysis. We attempt to elucidate the fundamental physical principles that govern the energy conversion by the upconversion materials. In addition, we intend to draw attention to recent technologies in upconversion nanomaterials integrated with photovoltaic and photocatalytic devices. This review also provides a useful guide to materials synthesis and optoelectronic device fabrication based on lanthanide-doped upconversion materials.
154 citations
TL;DR: The fluorescence intensity of N,N-dimethyl-4-((2-methylquinolin-6-yl)ethynyl)aniline exhibits an unusual intensification with increasing temperature, by activating more vibrational bands and leading to stronger TICT emissions upon heating in dimethyl sulfoxide.
115 citations
TL;DR: The mechanistic investigation revealed that energy-band matching is the major factor in the observed enhancement of photocatalytic activity.
Abstract: Heterostructures play an important role not only in the manufacture of semiconductor devices, but also in the field of catalysis. Herein, we report the synthesis of PdO/TiO2 and Pd/TiO2 heterostructured nanobelts by means of a simple co-precipitation method, followed by a reduction process using surface-modified TiO2 nanobelts as templates. The as-obtained heterostructures were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and UV/Vis diffuse reflectance spectroscopy. PdO and Pd nanoparticles with a size of about 1.3 and 1.6 nm were assembled uniformly on the surface of TiO2 nanobelts, respectively. Compared with TiO2 nanobelts, PdO/TiO2 and Pd/TiO2 hybrid nanobelts exhibit enhanced photocatalytic activity upon UV and visible-light irradiation. Photoelectrochemical technology was used to study the heterostructure effect on enhanced photocatalytic activity. Our mechanistic investigation revealed that energy-band matching is the major factor in the observed enhancement of photocatalytic activity.
57 citations
TL;DR: Tuning the luminescence lifetimes of upconversion nanocrystals through lanthanide doping provides new opportunities for optical multiplexing in the time domain for applications in imaging and security marking as mentioned in this paper.
Abstract: Tuning the luminescence lifetimes of upconversion nanocrystals through lanthanide doping provides new opportunities for optical multiplexing in the time domain for applications in imaging and security marking.
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...
TL;DR: In this paper, two complementary dyes are incorporated in dye-sensitized solar cells to solve the optical absorption limitation of organic dyes for DSCs, which is a major limitation of using organic dye for DSSs.
Abstract: A major limitation of using organic dyes for dye-sensitized solar cells (DSCs) has been their lack of broad optical absorption. Cosensitization, in which two complementary dyes are incorporated int...
TL;DR: The emission intensities of a fluorescent monomer-aggregate coupled system, based on 7-(dimethylamino)-coumarin-3-carbaldehyde, exhibit ultra-low temperature dependence with a low temperature coefficient of only 0.05% per °C, by judicious selection of the excitation wavelength.
Journal Article•
TL;DR: The best evidence in the field of hip fractures has attracted increasing attention and systematic reviews on hip fractures from China have been increasingly more frequent during the past 6 years, particularly in 2012.
Abstract: Background The objective of this study was to analyze the trend in the publication of systematic reviews on hip fractures through a bibliometric approach. Methods Literature including systematic reviews or meta-analyses on hip fractures was searched from the ISI Web of Science citation database. The search results were analyzed in terms of geographical authorship and frequency of citation by country, institution, author, and periodical distribution. Results A total of 654 published systematic reviews from 1995 to 2013 in 48 countries or regions were retrieved. The United States (171) was the predominant country in terms of the number of total publications, followed by the United Kingdom (149), Canada (120), Australia (76), and China (54). The number of systematic reviews significantly increased during the last 6 years, especially in China. The production ranking changed in 2012, at which time the United States and China were the leaders in the yearly production of systematic reviews on hip fractures. The amount of literature (27 publications) from China contributed almost one-quarter of the total literature (109 publications) in 2012. However, the average number of citations of each article from China was still low (6.70), while the highest number of citations of each article was from Sweden (193.36). The references were published in 239 different journals, with 15 journals contributing to 41.3% of the systematic reviews on hip fractures. The two journals that contributed the most were Osteoporosis International (10.6%) and the Cochrane Database of Systematic Reviews (7.6%). The predominant institution in terms of the number of publications was McMaster University (36) in Canada. Conclusions The best evidence in the field of hip fractures has attracted increasing attention. Systematic reviews on hip fractures from China have been increasingly more frequent during the past 6 years, particularly in 2012.
TL;DR: Porous microspherical Li4Ti5O12 aggregates (LTO-PSA) can be successfully prepared by using porous spherical TiO2 as a titanium source and lithium acetate as a lithium source followed by calcinations.
Abstract: Porous microspherical Li4Ti5O12 aggregates (LTO-PSA) can be successfully prepared by using porous spherical TiO2 as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO-PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO-PSA at 30 C is as high as 141 mA h g(-1), whereas that of normal Li4Ti5O12 powders prepared by a sol-gel method can only achieve 100 mA h g(-1). This improved rate performance can be ascribed to small Li4Ti5O12 nanocrystallites, a three-dimensional mesoporous structure, and enhanced ionic conductivity.
TL;DR: The metal-organic complex offers unique optical and electronic properties arising from the interplay between the inorganic metal and the organic ligand as mentioned in this paper, and the ability to modify chemical structure through control over metalligand interaction on a molecular level could directly impact the properties of the complex.
Abstract: The design and characterization of metal–organic complexes for optoelectronic applications is an active area of research. The metal–organic complex offers unique optical and electronic properties arising from the interplay between the inorganic metal and the organic ligand. The ability to modify chemical structure through control over metal–ligand interaction on a molecular level could directly impact the properties of the complex. When deposited in thin film form, this class of materials enable the fabrication of a wide variety of low-cost electronic and optoelectronic devices. These include light emitting diodes, solar cells, photodetectors, field-effect transistors as well as chemical and biological sensors. Here we present an overview of recent development in metal–organic complexes with controlled molecular structures and tunable properties. Advances in extending the control of molecular structures to solid materials for energy conversion and information technology applications will be highlighted.
TL;DR: Composite heteronanostructures hold promise for high photocatalytic efficiency for water splitting and the degradation of organic pollutants, but their photoc atalytic activity under broadband excitation has been challenging, until now.
Abstract: Composite heteronanostructures hold promise for high photocatalytic efficiency for water splitting and the degradation of organic pollutants. However, their photocatalytic activity under broadband excitation has been challenging, until now.