Z.B. Hu

Spectroscopic properties of Er3+ ions in transparent oxyfluoride glass ceramics containing CaF2 nano-crystals

In this paper, the spectroscopic properties of Er3+-doped oxyfluoride glass ceramics containing CaF2 nano-crystals are systematically investigated. X-ray diffraction (XRD) and transmission electron microscope (TEM) experiments confirmed the formation of CaF2 nano-crystals in the glassy matrix. Based on the Judd–Ofelt theory, the intensity parameters Ω2,4,6, spontaneous emission probability, radiative life, radiative quantum efficiency, width of the emission line, stimulated emission cross-section and gain spectrum were evaluated, and the effect of Er3+ doping concentration on the spectroscopic properties of the transition is discussed. For glass ceramics, intense red and weak green up-conversion luminescence were observed and ascribed to two-photon absorption processes.

Effects of doping Y on crystal structure and catalytic activity of α-Bi2Mo3O12

Abstract The single phase Y0·2Bi1·8Mo3O12 and α-Bi2Mo3O12 catalysts have been synthesised by solid state reaction, and the Y0·2Bi1·8Mo3O12 shows better catalytic performance than α-Bi2Mo3O12 in the selective oxidation of isobutene to methacrolein. X-ray powder diffraction structural analysis, X-ray photoelectron spectroscopy and O2 temperature programmed desorption have been used to reveal the effects of doping Y on the crystal structure and catalytic activity of α-Bi2Mo3O12 induced by Y substitution for Bi. It is found that when Bi in α-Bi2Mo3O12 crystal structure is partially substituted by Y with lower electronegativity, the electronic densities of oxygen will increase, which could improve the rate determining α-H abstraction at Bi sites in the selective oxidation of isobutene to methacrolein. On the other hand, the partially regularised MoO4 tetrahedra also promote the catalytic selectivity to methacrolein due to the decrease in oxidation ability. Besides, the longer interatomic distances between Mo3 and Bi in the principal cleavage plane (010) and (010) might result in the lesser catalytic activity of Mo3 sites.

The effect of Zr addition on the formation and structural properties of 3:29 compounds in the Fe-Nd-Ti-Zr system

A new series of 3:29 compounds in the Fe–Nd–Ti–Zr quaternary system were synthesized successfully. The formation and structural properties were studied by means of powder x-ray and powder neutron diffraction. The results reveal that only a small amount of Zr content can exist in the 3:29-type compounds in the Fe–Nd–Ti–Zr quaternary system. Higher Zr content induces the formation of rhombohedral Th2Zn17-type phase. In the structures of 3:29-type compounds, the Zr content partially substitutes for Nd and enters the 2a and 4i crystallographic sites exclusively. Upon Zr substitution, the lattice parameters a, b, c and the unit cell volumes V of (Nd,Zr)3(Fe,Ti)29 compounds decrease monotonically and their intrinsic magnetic properties, including the Curie temperature and saturation magnetization, lessen as well.

Thermal expansion properties of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (Ln = Er and Y)

Structures and thermal expansion properties of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (Ln = Er and Y) have been investigated by X-ray powder diffraction. Rietveld analysis results of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} indicate that compounds Er{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (0 {<=} x {<=} 0.3) and Y{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (0 {<=} x {<=} 0.2) crystallize in orthorhombic structure and exhibit negative thermal expansion, while both monoclinic and orthorhombic compounds Er{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (1.7 {<=} x {<=} 2.0) and Y{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (1.8 {<=} x {<=} 2.0) possess positive coefficient of thermal expansion. The coefficients of linear thermal expansion of orthorhombic Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} change from negative to positive with increasing chromium content. Thermogravimetric and differential scanning calorimetry have been used to study the hygroscopicity and the phase transition temperature.