The parent compounds of the high-temperature cuprate superconductors are Mott insulators.It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mecha...The parent compounds of the high-temperature cuprate superconductors are Mott insulators.It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mechanism of high temperature superconductivity.A natural starting point is to elucidate the basic electronic structure of the parent compound.Here we report comprehensive high resolution angle-resolved photoemission measurements on Ca_2CuO_2Cl_2,a Mott insulator and a prototypical parent compound of the cuprates.Multiple underl.ying Fermi surface sheets are revealed for the first time.The high energy waterfall-like band dispersions exhibit different behaviors near the nodal and antinodal regions.Two distinct energy scales are identified：a d-wave-like low energy peak dispersion and a nearly isotropic lower Hubbard band gap.These observations provide new information of the electronic structure of the cuprate parent compound,which is important for understanding the anomalous physical properties and superconductivity mechanism of the high temperature cuprate superconductors.展开更多
Single crystalline calcium chloroborate（Ca2B5O9Cl） whiskers with uniform diameter have been fabricated by a two-step process. The precursor was firstly prepared by the sedimentation reaction between CaCl2, H3BO3 and...Single crystalline calcium chloroborate（Ca2B5O9Cl） whiskers with uniform diameter have been fabricated by a two-step process. The precursor was firstly prepared by the sedimentation reaction between CaCl2, H3BO3 and Na OH aqueous solutions, and then sintered at different temperatures for 6 h with KCl as flux. The XRD indicates that the product synthesized at 600 °C is Orthorhombic Ca2B5O9Cl. SEM and TEM results show that the Ca2B5O9Cl is whisker with the diameter about 0.2-0.5 μm and the length up to 15 μm. SAED analysis shows that the whisker is single crystalline and grows along [001] direction. The possible formation process and growth mechanism were proposed.展开更多
Ca2BO3Cl：Ce3＋, Ca2BO3Cl：Tb3＋, and Ca2BO3Cl：Ce3＋, Tb3＋ phosphors are synthesized by a high temperature solid-state reaction. The emission intensity of Ce3＋ or Tb3＋ in Ca2BO3Cl is influenced by the Ce3＋ or Tb3...Ca2BO3Cl：Ce3＋, Ca2BO3Cl：Tb3＋, and Ca2BO3Cl：Ce3＋, Tb3＋ phosphors are synthesized by a high temperature solid-state reaction. The emission intensity of Ce3＋ or Tb3＋ in Ca2BO3Cl is influenced by the Ce3＋ or Tb3＋ doping content, and the optimum concentrations of Ce3＋ and Tb3＋ are 0.03 tool and 0.05 mol, respectively. The concentration quenching effect of Ce3＋ or Tb3＋ in Ca2BO3Cl occurs, and the concentration quenching mechanism is d-d interaction for either Ce3＋ or Tb3＋. The Ca21303Cl：Ce3＋, Tb3＋ can produce colour emission from blue to green by properly tuning the relative ratio between Ce3＋ and Tb3＋, and the emission intensity of Tb3＋ in Ca2BO3Cl can be enhanced by the energy transfer from Ce3＋ to Tb3＋. The results indicate that Ca2BO3Cl：Ce3＋, Tb3＋ may be a promising double emission phosphor for UV-based white light emitting diodes.展开更多
基金Supported by the National Key Research and Development Program of China(2016YFA0300300)the National Natural Science Foundation of China(11334010 and 11534007)+1 种基金the National Basic Research Program of China(2015CB921000)the Strategic Priority Research Program(B)of Chinese Academy of Sciences(XDB07020300)
文摘The parent compounds of the high-temperature cuprate superconductors are Mott insulators.It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mechanism of high temperature superconductivity.A natural starting point is to elucidate the basic electronic structure of the parent compound.Here we report comprehensive high resolution angle-resolved photoemission measurements on Ca_2CuO_2Cl_2,a Mott insulator and a prototypical parent compound of the cuprates.Multiple underl.ying Fermi surface sheets are revealed for the first time.The high energy waterfall-like band dispersions exhibit different behaviors near the nodal and antinodal regions.Two distinct energy scales are identified：a d-wave-like low energy peak dispersion and a nearly isotropic lower Hubbard band gap.These observations provide new information of the electronic structure of the cuprate parent compound,which is important for understanding the anomalous physical properties and superconductivity mechanism of the high temperature cuprate superconductors.
基金Funded by the National Natural Science Foundation of China(No.51402323)the West Light Foundation of the Chinese Academy of Sciences(No.Y412031006)the Natural Science Foundation of Qinghai Province,China(No.2014-ZJ-938Q)
文摘Single crystalline calcium chloroborate（Ca2B5O9Cl） whiskers with uniform diameter have been fabricated by a two-step process. The precursor was firstly prepared by the sedimentation reaction between CaCl2, H3BO3 and Na OH aqueous solutions, and then sintered at different temperatures for 6 h with KCl as flux. The XRD indicates that the product synthesized at 600 °C is Orthorhombic Ca2B5O9Cl. SEM and TEM results show that the Ca2B5O9Cl is whisker with the diameter about 0.2-0.5 μm and the length up to 15 μm. SAED analysis shows that the whisker is single crystalline and grows along [001] direction. The possible formation process and growth mechanism were proposed.
基金Project supported by the National Basic Research Program of China(Grant No.2010CB327704)the National Natural Science Foundation for Distinguished Young Scholars of China(Grant No.60825407)+7 种基金the New Century Excellent Talents in University (Grant No.NCET-10-0220)the National Natural Science Foundation of China(Grant Nos.10974013,60978060,10804006,and 50902042)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20090009110027)Beijing Municipal Natural Science Foundation,China(Grant No.1102028)the Beijing Municipal Science & Technology Commission, China(Grant No.Z090803044009001)the Natural Science Foundation of Hebei Province,China(Grant No.E2010000283)the Fund from the Key Laboratory of Luminescence and Optical Information,Beijing Jiaotong University,Ministry of Education, China(Grant No.2010LOI12)the Excellent Doctor's Science and Technology Innovation Foundation of Beijing Jiaotong University(Grant No.2011YJS073)
文摘Ca2BO3Cl：Ce3＋, Ca2BO3Cl：Tb3＋, and Ca2BO3Cl：Ce3＋, Tb3＋ phosphors are synthesized by a high temperature solid-state reaction. The emission intensity of Ce3＋ or Tb3＋ in Ca2BO3Cl is influenced by the Ce3＋ or Tb3＋ doping content, and the optimum concentrations of Ce3＋ and Tb3＋ are 0.03 tool and 0.05 mol, respectively. The concentration quenching effect of Ce3＋ or Tb3＋ in Ca2BO3Cl occurs, and the concentration quenching mechanism is d-d interaction for either Ce3＋ or Tb3＋. The Ca21303Cl：Ce3＋, Tb3＋ can produce colour emission from blue to green by properly tuning the relative ratio between Ce3＋ and Tb3＋, and the emission intensity of Tb3＋ in Ca2BO3Cl can be enhanced by the energy transfer from Ce3＋ to Tb3＋. The results indicate that Ca2BO3Cl：Ce3＋, Tb3＋ may be a promising double emission phosphor for UV-based white light emitting diodes.
