The ultraviolet beam at 266nm was obtained by fourth harmonic generation of 1064nm Nd:YAG laser radiation through a nonlinear crystal K2Al2B2O7 (KABO).The fundamental frequency of a flash-lamp pumped Nd:YAG laser was ...The ultraviolet beam at 266nm was obtained by fourth harmonic generation of 1064nm Nd:YAG laser radiation through a nonlinear crystal K2Al2B2O7 (KABO).The fundamental frequency of a flash-lamp pumped Nd:YAG laser was doubled in a β-Ba2B2O4 crystal to generate a second harmonic output at the wavelength of 532nm,and then doubled again in the KABO crystal to generate the fourth harmonic output at 266nm.The optical conversion efficiency from 532 to 266 nm was investigated for the first time,and 13% was achieved.展开更多
In situ high pressure energy dispersive X-ray diffraction measurements on layered perovskite-like manganate Ca3Mn2O7 under pressures up to 35 GPa have been Performed by using diamond anvil cell with synchrotron radiat...In situ high pressure energy dispersive X-ray diffraction measurements on layered perovskite-like manganate Ca3Mn2O7 under pressures up to 35 GPa have been Performed by using diamond anvil cell with synchrotron radiation.The results show that the structure of layered perovskite-like manganate Ca3Mn2O7 is unstable under pressure due to the easy compression of NaCl-type blocks.The structure of Ca3Mn2O7 underwent two phase transitions under pressures in the range of 0-35GPa.One was at about 1.3GPa with the crystal structure changing from tetragonalt go orthorhombic.The other was at about 9.5GPa with the crystal structure changing form orthorhombic back to another tetragonal.展开更多
Rare earth europium(Eu(3+))-doped lithium tetraborate(Eu:Li_2B_4O_7) crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique(μT-Cz) for the first time. The grown crystals are subjecte...Rare earth europium(Eu(3+))-doped lithium tetraborate(Eu:Li_2B_4O_7) crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique(μT-Cz) for the first time. The grown crystals are subjected to powder x-ray diffraction(PXRD) analysis which reveals the tetragonal crystal structure of the crystals. UV–vis–NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO_3 and BO_4 bonding structure and the molecular associations are analyzed by Fourier transform infrared(FTIR) spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate(LTB) single crystal reveal that the observations of peaks at 258,297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission spectra.The chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931(Commission International d'Eclairage) color chromaticity diagram.展开更多
Nanoscale layered-perovskite La2.5-xK0.5+xMn2O7(0<x<0.5) have been prepared by the modified sol-gel method,and their structural,magnetic and electric properties have been studied.The experimental results show th...Nanoscale layered-perovskite La2.5-xK0.5+xMn2O7(0<x<0.5) have been prepared by the modified sol-gel method,and their structural,magnetic and electric properties have been studied.The experimental results show that these materials exhibit paramagnetic-to-ferromagnetic phase transitions at 183,216,230,238 and 249K for x=0.05,0.15,0.25,0.35 and 0.45,respectively.For all compositions of La2.5-xK0.5+xMn2O7 investigated here,we have observed no metal-nonmetal transition phenomena for the whole temperature region (80-300K).The nanoscale samples exhibit highly enhanced magnetoresistance (MR) effects especially at low temperatures (<TC).The MR behaviour can be explained by taking into account the two-dimensionality with anisotropy of the Mn-O networks and nanoscale grain size effect in the layered manganese perovskites.展开更多
The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the stru...The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the structural domain formation in this material often complicates the study of intrinsic material properties.It is crucial to fully characterize the structural domains for unrevealing underlying physics.Here,we report the domain imaging on Ca3Ru2O7 crystal using the reflection of polarized light at normal incidence.The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal,and gives rise to a peculiar contrast.The domain walls are found to be the interfaces between 90° rotated twin crystals by complementary magnetization measurements.A distinct contrast in reflectance is also found in the opposite cleavage surfaces,owing to the polar mode of the RuO6 octahedra.More importantly,the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain.Such an approach provides an efficient yet feasible method for structural domain characterization,which can also find applications in noncentrosymmetric crystals in general.展开更多
气氛环境下原位研究催化剂的烧结行为,能够为理解催化剂在预处理以及反应条件下的烧结机理和高稳定催化剂的设计提供重要的实验依据。本文以Au/CeO_(2)模型纳米催化剂为研究对象,利用环境透射电子显微镜原位观察其在O_(2)与CO气氛下的...气氛环境下原位研究催化剂的烧结行为,能够为理解催化剂在预处理以及反应条件下的烧结机理和高稳定催化剂的设计提供重要的实验依据。本文以Au/CeO_(2)模型纳米催化剂为研究对象,利用环境透射电子显微镜原位观察其在O_(2)与CO气氛下的高温动态烧结过程。实验发现,负载在CeO_(2)上的Au纳米颗粒在O_(2)与CO气氛环境中表现出不同的烧结行为,其在O_(2)气氛下具有较高的烧结速度,同时存在颗粒迁移与聚集长大(particle migration and coalescence,PMC)和奥斯特瓦尔德熟化(Ostwald ripening,OR)两种烧结过程;在CO气氛下烧结速度较慢,烧结过程以OR为主。对比不同气氛环境下烧结后催化剂的表面结构可知,CO增加了CeO_(2)表面台阶的数量以及表面氧空位浓度,增强了载体对Au颗粒的锚定作用,从而提升Au/CeO_(2)催化剂的稳定性。展开更多
文摘The ultraviolet beam at 266nm was obtained by fourth harmonic generation of 1064nm Nd:YAG laser radiation through a nonlinear crystal K2Al2B2O7 (KABO).The fundamental frequency of a flash-lamp pumped Nd:YAG laser was doubled in a β-Ba2B2O4 crystal to generate a second harmonic output at the wavelength of 532nm,and then doubled again in the KABO crystal to generate the fourth harmonic output at 266nm.The optical conversion efficiency from 532 to 266 nm was investigated for the first time,and 13% was achieved.
文摘In situ high pressure energy dispersive X-ray diffraction measurements on layered perovskite-like manganate Ca3Mn2O7 under pressures up to 35 GPa have been Performed by using diamond anvil cell with synchrotron radiation.The results show that the structure of layered perovskite-like manganate Ca3Mn2O7 is unstable under pressure due to the easy compression of NaCl-type blocks.The structure of Ca3Mn2O7 underwent two phase transitions under pressures in the range of 0-35GPa.One was at about 1.3GPa with the crystal structure changing from tetragonalt go orthorhombic.The other was at about 9.5GPa with the crystal structure changing form orthorhombic back to another tetragonal.
基金Project supported by the Department of Science and Technology–Science and Engineering Research Board(Grant No.SR/S2/LOP-0012/2011)the Government of India for Awarding Major Research Project,the University Grants Commission–Department of Atomic Research–Consortium for Scientific Research(Grant No.CSR–KN/CSR–63/2014–2015/503)the Kalpakkam and Indore,India
文摘Rare earth europium(Eu(3+))-doped lithium tetraborate(Eu:Li_2B_4O_7) crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique(μT-Cz) for the first time. The grown crystals are subjected to powder x-ray diffraction(PXRD) analysis which reveals the tetragonal crystal structure of the crystals. UV–vis–NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO_3 and BO_4 bonding structure and the molecular associations are analyzed by Fourier transform infrared(FTIR) spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate(LTB) single crystal reveal that the observations of peaks at 258,297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission spectra.The chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931(Commission International d'Eclairage) color chromaticity diagram.
文摘Nanoscale layered-perovskite La2.5-xK0.5+xMn2O7(0<x<0.5) have been prepared by the modified sol-gel method,and their structural,magnetic and electric properties have been studied.The experimental results show that these materials exhibit paramagnetic-to-ferromagnetic phase transitions at 183,216,230,238 and 249K for x=0.05,0.15,0.25,0.35 and 0.45,respectively.For all compositions of La2.5-xK0.5+xMn2O7 investigated here,we have observed no metal-nonmetal transition phenomena for the whole temperature region (80-300K).The nanoscale samples exhibit highly enhanced magnetoresistance (MR) effects especially at low temperatures (<TC).The MR behaviour can be explained by taking into account the two-dimensionality with anisotropy of the Mn-O networks and nanoscale grain size effect in the layered manganese perovskites.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2019YFA0308602 and 2016YFA0300500)the National Natural Science Foundation of China(Grant Nos.11804220,11774305 and 11974237)Natural Science Foundation of Shanghai(Grant No.20ZR1428900).
文摘The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the structural domain formation in this material often complicates the study of intrinsic material properties.It is crucial to fully characterize the structural domains for unrevealing underlying physics.Here,we report the domain imaging on Ca3Ru2O7 crystal using the reflection of polarized light at normal incidence.The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal,and gives rise to a peculiar contrast.The domain walls are found to be the interfaces between 90° rotated twin crystals by complementary magnetization measurements.A distinct contrast in reflectance is also found in the opposite cleavage surfaces,owing to the polar mode of the RuO6 octahedra.More importantly,the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain.Such an approach provides an efficient yet feasible method for structural domain characterization,which can also find applications in noncentrosymmetric crystals in general.
文摘气氛环境下原位研究催化剂的烧结行为,能够为理解催化剂在预处理以及反应条件下的烧结机理和高稳定催化剂的设计提供重要的实验依据。本文以Au/CeO_(2)模型纳米催化剂为研究对象,利用环境透射电子显微镜原位观察其在O_(2)与CO气氛下的高温动态烧结过程。实验发现,负载在CeO_(2)上的Au纳米颗粒在O_(2)与CO气氛环境中表现出不同的烧结行为,其在O_(2)气氛下具有较高的烧结速度,同时存在颗粒迁移与聚集长大(particle migration and coalescence,PMC)和奥斯特瓦尔德熟化(Ostwald ripening,OR)两种烧结过程;在CO气氛下烧结速度较慢,烧结过程以OR为主。对比不同气氛环境下烧结后催化剂的表面结构可知,CO增加了CeO_(2)表面台阶的数量以及表面氧空位浓度,增强了载体对Au颗粒的锚定作用,从而提升Au/CeO_(2)催化剂的稳定性。
