L. T. Yang

Effects of Cu on crystallographic and magnetic properties of Sm(Co,Cu)7

We have investigated the structural stability and magnetic properties of SMCo7-xCu, compounds with the TbCu7-type structure using x-ray powder diffraction and magnetic measurement. A large solid solution with 0.8 less than or equal to x less than or equal to 4.0 in SMCo7-xCux compounds has been observed. Both the lattice parameters and unit cell volume increase with increasing Cu content. SMCo7-xCux compounds exhibit ferromagnetic order. A strong uniaxial magnetocrystalline anisotropy with an anisotropy field as high as 20 T is obtained with x = 0.8 at 5 K. However, the saturation magnetization and Curie temperature decrease with increasing Cu content.

Upconversion luminescence from E-2 state of Cr3+ in Al2O3 crystal by infrared femtosecond laser irradiation

Visible upconversion luminescence was observed in Cr3+: Al2O3 crystal under focused femtosecond laser irradiation. The luminescence spectra show that the upconversion luminescence originates from the 2E-4A2 transition of Cr3+. The dependence of the fluorescence intensity of Cr3+ on the pump power reveals that a two-photon absorption process dominates in the conversion of infrared radiation to the visible emission. It is suggested that the simultaneous absorption of two infrared photons produces the population of upper excited states, which leads to the characteristic visible emission from 2E state of Cr3+.

Three-photon-excited upconversion luminescence of Ce3+: YAP crystal by femtosecond laser irradiation

Infrared to ultraviolet and visible upconversion luminescence was demonstrated in trivalent cerium doped YAlO(3) crystal (Ce(3+): YAP) under focused infrared femtosecond laser irradiation. The fluorescence spectra show that the upconverted luminescence comes from the 5d-4f transitions of trivalent cerium ions. The dependence of luminescence intensity of trivalent cerium on infrared pumping power reveals that the conversion of infrared radiation is dominated by three-photon excitation process. It is suggested that the simultaneous absorption of three infrared photons pumps the Ce(3+) ion into upper 5d level, which quickly nonradiatively relax to lowest 5d level. Thereafter, the ions radiatively return to the ground states, leading to the characteristic emission of Ce(3+).

Three-photon-excited upconversion luminescence of YVO4 single crystal by infrared femtosecond laser irradiation.

We report on the upconversion luminescence of a pure YVO4 single crystal excited by an infrared femtosecond laser. The luminescent spectra show that the upconversion luminescence comes from the transitions from the lowest excited states 3T1, 3T2 to the ground state 1A1 of the VO4 3-. The dependence of the fluorescence intensity on the pump power density of laser indicates that the conversion of infrared irradiation to visible emission is dominated by three-photon excitation process. We suggest that the simultaneous absorption of three infrared photons promotes the VO4 3- to excited states, which quickly cascade down to lowest excited states, and radiatively relax to ground states, resulting in the broad characteristic fluorescence of VO4 3-.

Self-formation of quasiperiodic void structure in CaF2 induced by femtosecond laser irradiation

We report the self-formation of quasiperiodic void structure with the length of several hundred micrometers inside the CaF2 crystal. The quasiperiodical voids along the propagation direction of the laser beam were formed spontaneously after the irradiation of a single femtosecond laser beam which was focused at a fixed point inside the crystal sample. The length of the void array varied with the focal depth beneath the sample surface. The possible mechanism of the self-formed void structure was discussed.

Compounds and phase relations in the SrO-Fe2O3-CuO, SrO-Fe2O3-Gd2O3 and Gd2O3-Fe2O3-CuO ternary systems

The subsolidus phase relations in the SrO-Fe2O3-CuO, SrO-Fe2O3-Gd2O3 and Gd2O3-Fe2O3-CuO systems have been investigated by the means of X-ray powder diffraction (XRD). All samples were synthesized in the air at 960 degreesC. There are nine binary compounds in the system SrO-Fe2O3-CuO. This system can be divided into twelve three-phase regions. A new ternary compound Sr7Fe17CuO34 is identified. There are eight binary compounds and no ternary compound in the SrO-Fe2O3-Gd2O3 system. Nine three-phase regions lie in this system. In the Gd2O3-Fe(2)9O(3)-CuO system, there are four binary compounds and no ternary compound. This system can be divided into five three-phase regions. The crystal structure of the binary compound SrGd2O4 was determined by powder XRD, this compound belongs to an orthorhombic structure with space group Pnma. The lattice parameters are a = 10.1226(1) Angstrom, b = 3.4720(0) c = 12.0482(2) Angstrom

Self-formation of void array in Al 2 O 3 crystal by femtosecond laser irradiation

The femtosecond laser induced void array inside Al2O3 crystals was discussed. The void array was formed spontaneously under the irradiation of a single beam of infrared femtosecond laser which was focused at a fixed point inside the Al2O3 crystal sample. It was found that the regular voids only could be fabricated near the sample surface, which was different from the situation in CaF2 single crystal reported before. The possible mechanism of the phenomena was also discussed.

Low-temperature synthesis and characterization of GaN nanocrystals from gallium trichloride precursor

Gallium nitride (GaN) has been synthesized by reacting gallium trichloride with ammonia (NH(3)) at low temperatures ranging from 500 to 1000 degreesC for 12 h. X-ray diffraction, transmission electron microscopy, infrared, and Raman backscattering spectra revealed that the synthesized GaN powder consists of single-phase nano-sized crystallites with the wurtzite-type structure. The average size of the crystals decreases with the reaction temperature from approximately similar to63 nm at 1000 degreesC to similar to5 nm at 500 degreesC. GaOCl and epsilon-Ga(2)O(3) are the intermediate products during synthesis of the GaN. Characteristic shifts of the Raman peaks are associated with the change in crystal size. The band-edge emission of GaN at 361 nm was observed on room temperature photoluminescence spectra exclusively for the sample synthesized at 1000 degreesC, while a new and broad emission band appeared with the center ranging from 827 to 765 nm for the samples synthesized between 500 and 800 degreesC.

Enhancement of superconducting transition temperature via Ba doping in RuSr2-xBaxGdCu2O8 (x <= 0.1)

The crystal structure and superconducting properties of RuSr2−xBaxGdCu2O8 (0⩽x⩽0.1) have been investigated. X-ray powder diffraction (XRD) patterns show that the solid solution range is 0⩽x⩽0.1. The superconducting transition temperature was raised up to 35 K (zero) and 62 K (onset) for x=0.07, from 16 K (zero) and 45 K (onset) for x=0.0, and then TC decreases with x when x>0.07. Rietveld refinement for XRD data of RuSr2−xBaxGdCu2O8 show that the apical Cu–O(1) bond length increases with an increase of x, while the Ru–O(1) bond length decreases, This may account for the enhancement of the superconducting transition temperature.

Crystal structure and physical properties of FeSr2GdCu2O7+δ

A new Fe–Sr–Gd–oxide–cuprate compound FeSr2GdCu2O7+δ (Fe1212) was successfully synthesized by solid-state reaction. X-Ray diffraction data indicate that the sample is single phase. A Rietveld refinement of the structure was carried out. This compound has a 1212-type structure of a tetragonal symmetry. The lattice parameters are a=3.8457(1) A, c=11.3875(2) A and the space group is P4/mmm. Magnetization measurements show that this compound exhibits paramagnetic behavior above 5 K. Resistance measurements show that the sample has a semiconductor-like behavior.