查看更多>>摘要：The elimination of pollutants from diesel exhaust has received widespread research attention as they cause serious air pollution and pose a threat to human health.Catalytic post-treatment technology is one of the most effective and universal technologies to treat diesel exhaust pollutants.The design and development of efficient and low-cost catalysts is the key factor to realize the wide application of cat-alytic post-treatment technology.Cerium(Ce)-based oxides with specific morphologies are widely used to eliminate pollutants in diesel vehicle exhaust due to their unique physical and chemical properties,such as high catalytic activity,low cost and non-toxicity.In this review,the preparation methods of Ce-based oxide materials with specific morphologies,such as nanoparticles,nanocubes,nanorods,nano-fibers,and multi-stage pores,are introduced in detail,and the research progress on using these catalysts for the removal of carbon monoxide,hydrocarbons,soot particles,nitrogen oxides,and other pollutants from diesel exhaust is reviewed in detail.Finally,the unresolved issues associated with using Ce-based oxide catalysts with a specific morphology to catalytically remove pollutants from diesel exhaust are highlighted,and future application prospects and development directions are discussed.
查看更多>>摘要：Full-spectrum phosphor-converted white-light-emitting diodes(pc-WLED)are emerging as a main-stream technology in semiconductor lighting.Nevertheless,high-performance blue phosphor which can be excited efficiently by a 400 nm NUV diode chip is still lacking.Herein,we present a blue-emitting Na3KMg7(PO4)6∶Eu2+phosphor synthesized by the solid-reaction method.Particularly,we find that the using of Li2CO3 as flux can significantly improve the crystal quality and thus the emission efficiency of the phosphor.Meanwhile,the excitation peak of the phosphor shifts from 365 to 400 nm,which is pivotal for efficient NUV(400 nm)diode chip excitation.The practical Eu2+concentration is also enhanced by using Li2CO3 as flux,and the absorption efficiency is greatly increased.This phosphor ex-hibits superior PL thermal stability,namely retains 94％integrated photoluminescence intensity at 150 ℃ of that at 25 ℃.As a result,the optimized phosphor shows an emission band peaked at 437 nm with a bandwidth of 40 nm and a high external photoluminescence quantum yield of 51.7％.Finally,a pc-WLED was fabricated by using NKMPO∶Eu2+blue,Sr2SiO4∶Eu2+green,CaAlSiN3∶Eu2+red phosphors,and a 400 nm NUV diode chip.It shows a high color rendering index of Ra=96.4 and a correlated color temperature of 4358 K.These results prove that NKMPO∶Eu2+is a promising blue phosphor for full-spectrum WLED based on NUV diode chips.
查看更多>>摘要：Red phosphor is an important component of the phosphor-converted white light-emitting diodes(pc-WLEDs).The development of the novel red phosphor with excellent luminescence properties is of great significance for high performance WLEDs.In this study,NaGd0.4Eu0.6Mg1-xZnxWO6 red phosphors with excellent luminescence properties were successfully synthesized and systematically investigated.Our results show that the Zn2+-doping concentration has significant effect on the microstructures and luminescence properties of the NaGd0.4Eu0.6Mg1-xZnxWO6 phosphors.The NaGd0.4Eu0.6Mg1-xZnxWO6(0≤ x ≤ 0.7)samples are well crystallized pure solid solution sub-microcrystals,whereas the phase purity gradually decreases at 0.7＜x ≤ 1.0.The NaGd0.4Eu0.6Mg1-xZnxWO6(0＜x ≤ 0.5)phosphors have stronger emissions than NaGd0.4Eu0.6MgWO6,and the optimized NaGd0.4Eu0.6Mg0.9Zn0.1WO6 phosphor possesses the best luminescence properties including thermal stability,CIE chromaticity coordinate,life time and quantum yield.The packaged WLED using NaGd0.4Eu0.6Mg0.9Zn0.1WO6 phosphor emits bright white light with higher CRI,lower CCT,and chromaticity coordinate close to the pure white light.The developed NaGd0.4Eu0.6Mg1-xZnxWO6 phosphors have potential application in lighting and display.This work can offer an effective strategy for boosting luminescence properties of tungstate phosphors with the double perovskite structure.
查看更多>>摘要：A novel green long afterglow material CaGeO3∶Tb3+was synthesized by high temperature solid phase method.According to the experimental results,CaGeO3∶Tb3+is a green long persistent luminescent(LPL)material with excellent performance.CaGeO3∶Tb3+shows LPL emission peak at 442,490.9,548.7,588.5 and 623.8 nm,corresponding to 5D3 to 7F4 and 5D4 to 7FJ(J=6,5,4,3)transitions of Tb3+.Its CIE co-ordinates are(0.27,0.50),indicating that the afterglow emission is close to the light of green region.In addition,after the excitation source is turned off,the afterglow time is longer than 90 min.After an interval of 7 h,the photo-stimulation luminescence(PSL)can be observed by using 980 nm laser cyclic excitation.The thermoluminescence(ThL)results show that there are three types of traps in the material and their depths are 0.666,0.774 and 0.892 eV respectively,which are caused by the doping of Tb3+.All the results show that CaGeO3∶Tb3+is an excellent long afterglow luminescent material.
查看更多>>摘要：A novel Eu2+-Eu3+co-activated ratiometric thermo-sensitive phosphor was developed and synthesized by solid-state reaction.The valence state of Eu,photoluminescence and thermo-sensitive performance of the phosphor prepared either in ambient air or carbothermally were investigated and discussed.The phosphor shows high sensitivity(Sa=0.0173 K-1,Sr=0.461％/K)and superior signal discriminability(△v～10380 cm-1).The thermo-sensitive performance is subject to the dual effects of different thermo-responses by Eu2+versus Eu3+combined with energy transfer from Eu2+to Eu3+,so that the sensitivity of the phosphor in the temperature range presents a non-monotonic trend.The development of the BaAl2B2O7∶Eu2+,Eu3+phosphor is not only expected to be relevant for application in the field of tem-perature sensing,but also of reference significance for improving the sensitivity by means of energy transfer between co-activator ions over a wider temperature range of Eu2+-Eu3+co-activated ratiometric thermo-sensitive phosphors.
查看更多>>摘要：Nd3+-doped tellurite glasses are promising materials for thermometers based on the fluorescence in-tensity ratio(FIR)technique.Nevertheless,at high Nd3+concentrations,energy transfer(ET)processes such as optical reabsorption and cross-relaxation can affect the Nd3+emission,which has been little explored in the literature.Therefore,the present work investigated the use of Nd3+-doped tellurite glass(samples doped with Nd3+at 0.2 mol％,0.5 mol％,2.0 mol％,and 4.0 mol％)in fluorescence thermometers,in the temperature range from 299 to 371 K.The results indicate a strong dependence of the FIR pa-rameters on the Nd3+concentration,due to changes in the emission band profiles caused by optical reabsorption of the Nd3+emissions and cross-relaxation processes.A decrease of the relative sensitivity of the ratio 4F5/2 → 4I9/2/4F3/2 → 4I9/2 is observed for samples doped with higher amounts of Nd3+.The maximum relative sensitivity at 299 K is 3.00％/K,which is the highest value among the reported Nd3+ions.
查看更多>>摘要：Our previous experimental observations show that the crystal structure of lanthanide luminescent complexes synthesized in aqueous solution usually contains a large number of coordination water molecules or free water molecules.In order to probe the influence of water molecules on luminescent processes of lanthanide complexes,the photoluminescence properties of Ln-FBA(Ln=Eu and Tb,FBA=p-fluorobenzoic acid)coordination polymers at different ambient temperatures,in different sol-vents and aqueous DMSO solutions with different volume concentrations were systematically investi-gated.The experiment results show that the presence of water molecules can promote the energy transfer from FBA ligand to Ln3+,at the same time,can cause luminescent non-radiation quenching of lanthanide ions.In addition,the variation of emission intensity ratio of 615 nm/591 nm peaks of Eu3+with increasing the volume concentration of H2O can be potentially used for the quantitatively detection of water traces in organic solvents.In order to suppress the non-radiation quenching caused by the water molecules,Ln-FBA(Ln=Eu and Tb)coordination polymers were embedded into the PVP matrix to prepare Ln-FBA@PVP hybrid materials.The photoluminescence investigation indicates that PVP can not only block the quenching effect of water molecules on luminescence,but also effectively sensitize Eu3+and Tb3+luminescence.These experimental conclusions are useful for probing the influence of water molecules on luminescent processes of lanthanide complexes,quantitatively detecting water traces in organic solvents and enhancing the photoluminescence intensity in lanthanide complexes.
查看更多>>摘要：Ce/BEA has great potential as a passive NOx absorber(PNA)to reduce the NOx emissions during the cold start phase especially in diesel engine for its high resistance to CO and suitable NOx desorption tem-perature range.However,as a novel material,its physical and chemical properties still remain unknown.In this work,Ce/BEA was synthesized by ion-exchange method to identify the active species in NOx adsorption,compared with aggregated Ce species in Ce/SiAlOx prepared by impregnation method.X-ray diffraction(XRD),high resolution-transmission electron microscopy(HR-TEM)and aberration-corrected-scanning transmission electron microscopy(AC-STEM)were performed to confirm the isolated single atom formation of Ce species in Ce/BEA.UV-vis diffraction reflection spectra(DRS)and X-ray photo-electron spectroscopy(XPS)were conducted to find the difference of chemical environment between the isolated Ce species and aggregated ones.PNA performance evaluation and temperature programmed reduction of hydrogen(H2-TPR)results show the high NOx storage capacity and active oxygen species quantity in Ce/BEA.It is also found that the main NOx adsorption species are Ce4+-O*rather than Ce3+.NOx-diffuse reflectance infrared Fourier transform spectroscopy(NOx-DRIFTS)confirms that the biden-tate nitrite species are the critical NOx adsorption intermediates and the conception of NOx adsorption and desorption processes is proposed.
查看更多>>摘要：The thermogravimetric analysis(TGA)experiments were carried out to reveal the mechanism of Zr and Mn doping on catalytic activity of CeO2 catalyst both fresh and after hydrothermal aging,and the lattice morphology and valence changes were characterized by means of Brunauer-Emmett-Teller(BET)method,X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and H2-temperature pro-grammed reduction(H2-TPR).Density functional theory(DFT)and molecular thermodynamics calcula-tions were applied to investigate the change in catalytic activity,crystal surface energy and crystal morphology caused by hydrothermal aging.The maximum reaction rate temperature of fresh Mn/CeO2(389 ℃)is similar to that of CeO2(371 ℃)and lower than that of Zr/CeO2(447 ℃),but the catalytic performance of CeO2 decreases more severely after hydrothermal aging.The catalyst crystals show different degrees of crystal surface migration after hydrothermal aging,which leads to the reduction of Ce3+/Ce4+ratio and the active sites shift.DFT calculations indicate that the doping of Zr and Mn reduces the surface energy of the low Miller indices surface and increases the oxygen vacancy formation energy,leading to better thermal stability and lower catalytic activity.The Zr and Mn doping also changes the adsorption energy and Gibbs free energy of H2O,which dominates the migration of(111)to(110)and(100)in the vapor environment.The crystal surface migration mechanism of CeO2 catalysts doped with Zr and Mn induced by H2O molecules at high temperature obtained in this study can provide a valuable addition to the regeneration of CeO2 catalysts in the after-treatment systems of diesel engines.
查看更多>>摘要：It is still a challenge to simultaneously enhance coercivity(Hcj)and remanence(Jr)of hot-deformed Nd-Fe-B magnet due to the coercivity-remanence trade-off dilemma.Here,we achieved this balance be-tween Hcj and Jr by flake Cu powder assisted DyF3 interflake addition.The Hcj increases from 1218 to 1496 kA/m and Jr increases from 1.32 to 1.34 T compared with the original magnet.Results show that the width of coarse grain layers reduces because of the introduction of flake Cu,which increases the contact areas of the adjacent grains at ribbon interfaces and suppresses the excessive growth of grains.The stronger degree of texture and higher density compared with the original magnet should take the re-sponsibility for the increase of Jr.Additionally,the aggregation regions of rare earth rich(RE-rich)phase reduce and the betterment of the microstructure is another reason for the enhancement of Jr in the flake Cu aided DyF3 hot-deformed magnet.This strategy of using flake powder additives provides a promising method for optimizing microstructure and enhancing magnetic properties of hot-deformed Nd-Fe-B magnets.
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