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排序方式: 共有333条查询结果,搜索用时 933 毫秒
1.
Calcium lanthanide oxyborate doped with rare-earth ions LnCa4O(BO3)3:RE3+ (LnCOB:RE, Ln=Y, La, Gd, RE=Eu, Tb, Dy, Ce) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos’ and Jφrgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. Jφrgensen, Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln,A) and charge transfer band Ect were calculated and compared with their excitation spectra.Eu3+ and Tb3+ ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce3+ ions do not show efficient luminescence and quench the luminescence of Tb3+ ions when Tb3+ and Ce3+ ions are co-doped into LnCOB. GdCOB doped with Dy3+ shows yellowish white light under irradiation of 254 nm light for the reason that Gd3+ ions transfer the energy from itself to Dy3+. Because of the existence of Gd3+, the samples of GdCOB:RE3+ show higher excitation efficiency than LaCOB:RE3+ and YCOB:RE3+, around 188 nm, which indicates that the Gd3+ ions have an effect on the host absorption and can transfer the excitation energy to the luminescent center such as Tb3+, Dy3+ and Eu3+. 相似文献
2.
Ab initio energetic calculations based on the density functional theory (DFT) and projector augmented wave (PAW) pseudo-potentials method were performanced to determine the crystal structural parameters and phase transition data of the polymorphic rare-earth sesquioxides Ln2O3 (where Ln=La-Lu, Y, and Sc) with A-type (hexagonal) and B-type (monoclinic) configurations at ground state. The calculated results agree well with the limited experimental data and the critically assessed results. A set of systematic and self-consistent crystal structural parameters, energies and pressures of the phase transition were established for the whole series of the A- and B-type rare-earth sesquioxides Ln2O3. With the increase of the atomic number, the ionic radii of rare-earth elements Ln and the volumes of the sesquioxides Ln2O3 reflect the so-called “lanthanide contraction”. With the increase of the Ln3+-cation radius, the bulk modulus of Ln2O3 decreases and the polymorphic structures show a degenerative tendency. 相似文献
3.
Svilen Bobev Paul H. Tobash Joe D. Thompson John L. Sarrao 《Journal of solid state chemistry》2005,178(6):2091-2103
A number of rare-earth alumo-silicides (R-Al-Si) have been synthesized from the corresponding elements by high-temperature reactions, carried out in excess of aluminum to serve as a flux. Under these experimental conditions, large single crystals of all R-Al-Si ternary phases were readily produced. The crystal structures these ternaries adopt were studied by means of powder and single-crystal X-ray diffraction and were classified as follows: (1) the early rare-earths (R=La, Ce, Pr, Nd, Sm, Gd) yield RAlxSi2−x, x∼1, non-stoichiometric ternary derivatives of the body-centered α-ThSi2-type; (2) the late rare-earths (R=Tb, Dy, Ho, Er, Tm) form stoichiometric R2Al3Si2 compounds that crystallize in the C-centered monoclinic Y2Al3Si2-type; (3) the divalent Eu and Yb produce EuAl2Si2 and YbAl2Si2 with the trigonal CaAl2Si2-type, whereas the last lanthanide element, Lu, forms LuAlSi with C-centered orthorhombic YAlGe-type. These structural trends are reviewed, and the evolution of the basic physical properties such as magnetism, heat capacity and electrical resistivity when moving across the series is described in detail. 相似文献
4.
E. Tomaszewicz 《Thermochimica Acta》2006,447(1):69-74
Reactivity in the solid state between CoWO4 and some rare-earth metal tungstates RE2WO6 (RE = Sm, Eu, Gd) was investigated by the XRD method. Two families of new isostructural cobalt and rare-earth metal tungstates, Co2RE2W3O14 and CoRE4W3O16, were synthesized. The Co2RE2W3O14 phases are formed by heating in air the CoWO4 and RE2WO6 compounds mixed at the molar ratio 2:1, while the CoRE4W3O16 phases are synthesized at the molar ratio of CoWO4/RE2WO6 equals to 1:2. The Co2RE2W3O14 phases as well as the CoRE4W3O16 compounds crystallize in the orthorhombic system. The Co2RE2W3O14 and CoRE4W3O16 compound melt above 1150 °C. A melting manner of the Co2RE2W3O14 and CoRE4W3O16 compounds was determined in an inert atmosphere. The formation of CoWO4−x phase was observed during heating in an inert atmosphere. 相似文献
5.
稀土磷酸盐发光材料的微波合成 总被引:5,自引:0,他引:5
稀土磷酸盐发光材料的微波合成徐文国,田一光,刘淼,刘海堂,方光华,庞文琴(吉林大学化学系,环境科学系,长春,130023)关键词微波合成,稀土磷酸盐,微晶玻璃,玻璃态,发光材料稀土磷酸盐发光材料的研究是当前材料科学的热门研究课题。它们一般通过高温固相... 相似文献
6.
The polyoxo rare-earth core
(Ln = Y, Gd, and Yb) has been synthesized from the appropriate rare-earth chloride hydrate and K2Se and Se in dmf (dimethylformamide). The cluster core is ligated with a variety of polyselenido chains in addition to a number of dmf molecules. The structure of the Gd8(dmf)13(4-O)(3-OH)12(Se3)(Se4)2(Se5)2 cluster, 1, was determined by X-ray diffraction methods. It is similar to an Eu cluster previously characterized. Two new clusters, Yb8(dmf)11(4-O)(3-OH)12(Se4)2(Se5)2Cl2·dmf, 2, and Y8(dmf)12(4-O)(3-OH)12(Se4)4Cl2·6 dmf, 3, have also been synthesized and characterized. Clusters 2 and 3 have the same octanuclear core of rare-earth atoms as the Gd cluster but contain two chloro ligands in two isomeric conformations in place of the Se
3
2-
ring in the Gd cluster. The geometry of the Ln
8 core is described as a triangulated dodecahedron with 3-OH groups capping the 12 faces. A 4-O atom centers the cluster with close contacts to four Ln atoms in an approximate tetrahedral arrangement. Pertinent crystallographic data are: Compound 1, monoclinic,
, a= 14.410(3) Å, b = 24.439(5) Å, c = 28.927(6) Å, = 101.05(3)°, V = 9998(3) Å3, T = 106(2) K, Z = 4; Compound 2, orthorhombic,
, a = 17.049(9) Å, b = 24.68(1) Å, c = 45.03(2)Å, V = 18,945(16) Å3, T = 153(2) K, Z = 8; Compound 3, monoclinic, C
2h
5
-P21/c, a =18.728(l) Å, b = 29.263( 1) Å, c = 20.548(1) Å, = 90.144(1)°, V = 11,261(1) Å3, T = 153(2) K, Z = 4. 相似文献
7.
2,6-Lutidine-N-oxide (LNO) complexes of rare-earth bromides of the composition
wheren = l for M = La, Pr, Nd, Sm, Gd, Ho, Er; andn = 0 for M = Y have been prepared and characterised by analyses, conductance and infrared data. Infrared spectra of the complexes
indicate that the coordination of ligand to the metal ion takes place through the oxygen of the ligand, and the water molecule
in the complexes present is coordinated to the metal. A coordination number of seven has been suggested to all the rare-earth
metal ions. 相似文献
8.
S. N. Achary B. R. Ambekar M. D. Mathews A. K. Tyagi P. N. Moorthy 《Thermochimica Acta》1998,320(1-2):239-243
Volume thermal expansion behaviour of a number of rare-earth oxyfluorides (REOF) have been studied using high-temperature X-Ray diffractometry (HT-XRD) in the 298–1075 K range in air. The studies revealed an anomalous expansion for each compound associated with phase transition. The phase transition temperature and the coefficient of volume thermal expansion of five compounds in REOF series determined by this method are reported and compared with our earlier results obtained by dilatometry. 相似文献
9.
Danuta M. Czakis-Sulikowska Joanna Radwańska-Doczekalska Teresa Miazek 《Monatshefte für Chemie / Chemical Monthly》1982,113(6-7):827-835
4,4-Dipyridyl and 2,2-dipyridyl complexes of rare-earth perchlorates of the formulaLn(4-dipy)8(ClO4)3HClO4 · 4H2O (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Y, 4-dipy=4,4-dipyridyl) andLn(2-dipy)3(ClO4)3 · 6H2O (Ln=Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Y, 2-dipy = 2,2-dipyridyl) have been synthesized. The IR spectra of these compounds and other physical properties are discussed.
4,4-Dipyridyl- und 2,2-Dipyridylkomplexe von Seltenerdmetallperchloraten
Zusammenfassung Es wurden 4,4-Dipyridylkomplexe des TypsLn(4-dipy)8(ClO4)3HClO4 · · 4 H2O mitLn=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Y und 2,2-Dipyridylkomplexe des TypsLn(2-dipy)3(ClO4)3 · 6 H2O mitLn=Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu und Y dargestellt. Die IR-Spektren und andere physikalische Eigenschaften werden diskutiert.相似文献
10.
Several CaF2 single crystals doped with trivalent rare-earth ions have been grown in the recent years in the form of bulk crystals by using the Bridgman method and in the form of thin films by using the MBE and LPE techniques. The spectroscopic, gain and laser properties of these crystals doped with Pr3+, on the one hand, and with Yb3+, Tm3+ or Er3+ ions, on the other hand, have been studied and are reviewed here for their laser potentials in the red and in the infrared spectral domains, respectively. 相似文献