Lei Wei

Synthesis and Characteristics of Hierarchical Co3O4 Powders

Co3O4 samples with hierarchical structure were synthesized successfully by the morphology-conserved transformation method. The XRD and XPS results show that the obtained samples have the typical spinel Co3O4 phase. The FT-IR spectrum shows that the precursors consist of Co–EG coordination polymer. The SEM images show that the obtained samples have the morphology of flower-like microspheres. The authors found that the key step of the obtaining of hierarchical Co3O4 flower-like microspheres by the morphology-conserved transformation method is to construct flower-like microstructures of the cobalt-containing precursors via manipulating the synthetic parameters in a facile ethylene glycol–mediated solvothermal reaction.

Thermal and spectroscopic characteristics of disordered melilite Nd:BaLaGa3O7 crystal

A disordered Nd:BaLaGa3O7 laser crystal was successfully grown by the Czochralski method. The effective segregation coefficient of Nd3+ in BaLaGa3O7 crystals was measured to be 1.12. A series of thermal properties, including specific heat, average linear thermal expansion coefficient, thermal diffusivity and thermal conductivity, were systematically determined as a function of temperature. The thermal conductivity increased with increasing temperature. The polarized absorption and emission spectra were measured at room temperature. Nd:BaLaGa3O7 possessed a large absorption bandwidth of 18 nm at 808 nm and an emission bandwidth of 32 nm at 1060 nm. According to the Judd–Ofelt theory, the spontaneous transition probabilities, the fluorescence branching ratios, and the radiation lifetime were calculated. The stimulated emission cross section for the4F3/2 → 4I11/2 transition was calculated to be 4.24 × 10−20 cm2. Thermal and optical properties have shown that Nd:BaLaGa3O7 crystals are potential alternative gain media for ultrafast lasers.

Optical, dielectric and ferroelectric properties of KTa0.63Nb0.37O3 and Cu doped KTa0.63Nb0.37O3 single crystals

KTa0.63Nb0.37O3 and Cu doped KTa0.63Nb0.37O3 single crystals were grown by the Czochralski method. The phase, optical and electric properties were characterized. The differences of XRD and color for KTa0.63Nb0.37O3 and Cu doped KTa0.63Nb0.37O3 single crystals are observed. Emission bands corresponding to Cu0 and Cu+ except of emission bands originating from KTa0.6Nb0.4O3 host were observed in the emission spectra of the KTa0.63Nb0.37O3:Cu single crystals. On the basis of these differences, we speculate the dominating existence of Cu0 and residual existence of Cu+ in KTa0.63Nb0.37O3 single crystal. The existence of Cu0 in KTa0.63Nb0.37O3 single crystal influences the optical and dielectric properties of crystal. The higher dielectric constant of Cu doped KTa0.63Nb0.37O3 single crystal than that of pure KTa0.63Nb0.37O3 single crystal is induced by the decrease of the resistance of the grain.

Effects of EDTA additives on optical properties of rapidly grown KDP single crystals

Potassium dihydrogen orthophosphate (KDP) single crystals were grown by the ‘point seed’ rapid growth technique from aqueous solutions with the addition of ethylene diamine tetraacetic acid (EDTA). Influences of EDTA additives on phase, growth rate, transmittance, and laser damage threshold were studied carefully. X-ray diffraction patterns indicated that the EDTA additives benefit to the crystallinity of KDP crystals. Also, with the addition of EDTA in the growth solution, the growth rate of prismatic sector was accelerated and the dead zone was decreased. The transmittance spectra showed that EDTA additives had obvious influence on the ultraviolet transmittance, but did not influence the transmittance in visible light region. And the appropriate amount of EDTA additives decreased the laser damage threshold. The improvements of optical properties for these KDP single crystals related to the coordinate bonds between EDTA and anionic impurities.