Red luminescence phosphor materials are important in practical applications because they are one of the three primary colors of light and are advantageous for improving color rendering in white light ...emitting diodes (LEDs). In particular, for red phosphor materials for white LED applications, Eu2+- or Ce3+-doped oxide materials are desired instead of non-oxides, such as nitride and fluorides, from the viewpoints of cost and safety in synthesis. However, blue-light excitable red luminescent oxide phosphor materials are extremely limited; thus, there are insufficient design concepts as to what type of matrix crystal is suitable for expression. Therefore, this review focuses on the coordination environment of the luminescent centers of Eu2+ and Ce3+ in the oxide lattice, which can be described as a crystal field. Specifically, luminescence properties and local structures in phosphors composed of oxide hosts with strong crystal fields, such as NaMgPO4:Eu2+, M3Sc4O9:Ce3+ (M = Ba and Sr), and BaCa2Y6O12:Ce3+, are discussed. Finally, based on the description in this review, a concept that is useful for realizing red luminescence in oxide hosts is presented.
Red luminescence phosphor materials are important in practical applications because they are one of the three primary colors of light and are advantageous for improving color rendering in white light ...emitting diodes (LEDs). In particular, for red phosphor materials for white LED applications, Eu2+- or Ce3+-doped oxide materials are desired instead of non-oxides, such as nitride and fluorides, from the viewpoints of cost and safety in synthesis. However, blue-light excitable red luminescent oxide phosphor materials are extremely limited; thus, there are insufficient design concepts as to what type of matrix crystal is suitable for expression. Therefore, this review focuses on the coordination environment of the luminescent centers of Eu2+ and Ce3+ in the oxide lattice, which can be described as a crystal field. Specifically, luminescence properties and local structures in phosphors composed of oxide hosts with strong crystal fields, such as NaMgPO4:Eu2+, M3Sc4O9:Ce3+ (M = Ba and Sr), and BaCa2Y6O12:Ce3+, are discussed. Finally, based on the description in this review, a concept that is useful for realizing red luminescence in oxide hosts is presented.
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•The nanostructured nitrogen-doped La2Ti2O7 was successfully synthesized.•The high degree of nitrogen doping was accomplished by the sophisticated synthesis.•The nanostructurization ...and the nitrogen-doping enhanced photocatalytic activity.•Triethanolamine played important roles in the synthesis of nitrogen-doped La2Ti2O7.•The particle size of La2Ti2O7 was much smaller than that of the conventional ones.
A series of N-doped La2Ti2O7 nanocrystal for photocatalytic NOx oxidation are successfully prepared by a two-steps process including hydrothermal reaction and heat treatment under NH3 flow. The effects of different nitrogen doping amounts on the structure, optical property and photocatalytic activity of the obtained N-doped La2Ti2O7 are investigated. The photocatalytic activity and stability of the N-doped La2Ti2O7 samples are evaluated through photocatalytic oxidation of NOx under UV and visible light irradiation. The nanosheet morphology of N-doped La2Ti2O7 is originated from La2Ti2O7 precursor synthesized by hydrothermal reaction. The addition of triethanolamine (TEA) in the hydrothermal reaction largely affects the morphology of La2Ti2O7 to form nanocrystal. The light absorption of La2Ti2O7 nanocrystal is cut off at 338 nm, while the N-doped La2Ti2O7 nanocrystals exhibit the extended light absorption up to 560 nm. It is found that the N doping into La2Ti2O7 enhances absorption in the visible light region to exhibit higher activity for photocatalytic oxidation of NO gas. The optimized N-doped La2Ti2O7 nanocrystal with 4.79 at% of nitrogen dopant possesses the best photocatalytic NOx oxidation activity under both ultraviolet and visible light irradiation compared with N-doped La2Ti2O7 samples obtained by hydrothermal reaction without TEA or flux synthesis of La2Ti2O7 and the subsequent treatment with NH3. The enhancement of photocatalytic activity should originate from simultaneous achievement of large specific surface area and strong visible light absorption due to the large amount of nitrogen dopants.
Pollen morphology varies at inter- and intraspecific levels. Its interaction with pollinator behavior and morphology determines the probability of successful pollination. We tested whether pollen ...morphology promoting successful pollination differs depending on pollinator taxa in a generalist shrub,
Weigela hortensis
(Caprifoliaceae). We identified flower visitors carrying pollen from anthers to stigmas and compared the spine length and diameter of the pollen grains they carried. We found that pollen on the bodies of bumble bees and hunch-back flies and the scopae of small bees (including andrenid bees) contributed to seed production. Pollen grains on the bodies of bumble bees had longer spines than those on the scopae of andrenid bees or the bodies of hunch-back flies. Pollen grains on the bodies of bumble bees and the scopae of andrenid bees had larger diameters than those on hunch-back flies. Bumble bees collected pollen grains with shorter spines and larger diameters on their corbiculae while andrenid bees collected pollen grains with shorter spines and intermediate diameters on their scopae. The differences in morphology of pollen carried by pollinators reflected the tendency of bees to collect pollen with specific morphology into corbiculae/scopae. Our findings suggest that pollen morphology has diversified to facilitate successful pollination by pollinating partners.
It is well known that the functionality of inorganic materials strongly depends on the chemical composition, morphology, particle size, crystal facet, etc., which are strongly influenced by the ...synthesis process. The precise control of the synthesis process is expected to lead to the discovery of new functionality and improvement of the functionality of materials. For example, in a high-temperature solid-phase reaction, it is difficult to control the morphology of nanocrystals. On the other hand, synthesizing functional materials using solution processes, such as hydrothermal and solvothermal reactions, makes it possible to control the morphology and particle size precisely. Usually, the solution process is strongly related to the dissolution reprecipitation mechanism. Therefore, the material composition can be strictly controlled and is suitable for forming fine particles with high crystallinity. In this review paper, the role of the solvent in the solution process, its effect on particle size and morphology of the transition metal oxide, and the related functional improvement will be focused. Furthermore, the direct formation of functional thin films by the solution process and the morphology control by non-oxide materials by the topotactic reaction will also be introduced.
Band structure modification via atomic doping and heterojunction formation with 2D Ti3C2Tx MXene.
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•A nanocomposite photocatalyst materials consisting of Ti,C-doped BiOBr/Ti3C2Tx MXene ...were successfully prepared.•The nanocomposites exhibited significantly improved NOx photodegradation ability under visible light irradiation.•The Ti and C doping cause band gap matching in band gap structure alignment between two materials.•The work have advanced the current approach on improving ability of photocatalyst materials.
NOx gas pollutants have induced continuous and massive damage to our health and environment. Photocatalysts are regarded as an efficient approach for NOx degradation. Various strategies have been devoted to optimizing photocatalyst performance. In this work, a bismuth oxybromide (BiOBr) photocatalyst was successfully combined with 2D Ti3C2Tx MXene by the solvothermal treatment. It is also found that partial decomposition of Ti3C2Tx has led the in situ doping sources for BiOBr/Ti3C2Tx nanocomposite. The photocatalytic NOx purification activity of the constructed (Ti, C) co-doped BiOBr/Ti3C2Tx nanocomposites was evaluated under light illumination. The results showed that up to 61% of NOx gas has been decontaminated as short as 10 min, exceeding the pristine BiOBr and P25 titania photocatalysts. Stable performance was also achieved after several cycles, which makes (Ti,C)-BiOBr/Ti3C2Tx nanocomposites a great promise for the long term and repeated utilization. The present strategy enhanced the photoinduced electron-hole separation and transfer of the heterostructured (Ti,C)-BiOBr/Ti3C2Tx. The match band structure configuration between (Ti,C)-BiOBr and Ti3C2Tx MXene and the synergistic process between photogenerated charge carrier transfer and intermediate Ti and C levels is discussed to explain the improved photocatalytic mechanism.
To meet the demand for smart windows, element doping is widely used as a powerful tool to customize the thermochromic properties of vanadium dioxide (VO2). Here, Mo-doped and F/Mo co-doped VO2 ...nanoparticles (NPs) are synthesized by the supercritical hydrothermal method. Doped VO2 films show excellent thermochromic properties including the reduced phase transition temperature (Tc = 47.4 °C), enhanced luminous transmittance (Tlum = 59.7%), and high solar energy modulation (ΔTsol=13.7%). Both X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) are utilized to study the local structure and chemical valence of the vanadium and molybdenum in the VO2 lattice. Combined Mott's with Peierls's models, the phase transition behavior of the doped VO2 is revealed deeply, i.e., depending on the octahedral symmetry and charge transfer. Additional electron injection seems to play a more important role than structural distortion in decreasing Tc, and F atoms exhibit a higher modulation ability of Tc. In addition, reduced reflectance by doping is responsible for the significantly improved Tlum, while ΔTsol is found to be more sensitive to the film structure. This work uncovers the mechanism behind the phase transition of Mo-doped and F/Mo co-doped VO2 NPs, which is expected to inspire the optimization strategy of element-doped VO2 films served as smart windows.
•Mo-doped and F/Mo co-doped VO2 nanoparticles (NPs) are hydrothermally synthesized.•Doped VO2 films possess excellent thermochromic properties.•Phase transition behavior is depended on octahedral symmetry and charge transfer.•Increased Tlum is attributed to the reduction of film reflectance.
Extensive attention has been focused toward studies on inexpensive and rare-earth-free garnet-structure vanadate phosphors, which do not have a low optical absorption due to the luminescence color ...being easily controlled by its high composition flexibility. However, bluish emission phosphors with a high quantum efficiency have not been found until now. In this study, we successfully discovered bluish-white emitting, garnet structure-based LiCa3MV3O12 (M = Zn and Mg) phosphors with a high quantum efficiency, and the detailed crystal structure was refined by the Rietveld analysis technique. These phosphors exhibit a broad-band emission spectra peak at 481 nm under near UV-light excitation at 341 nm, indicating no clear difference in the emission and excitation spectra. A very compact tetrahedral VO4 unit is observed in the LiCa3MV3O12 (M = Zn and Mg) phosphors, which is not seen in other conventional garnet compounds, and generates a bluish-white emission. In addition, these phosphors exhibit high quantum efficiencies of 40.1% (M = Zn) and 44.0% (M = Mg), respectively. Therefore, these vanadate garnet phosphors can provide a new blue color source for LED devices.
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