L. Wu

Photophysical properties and TPA optical limiting of two new organic compounds

The emission and optical limiting properties of two new organic compounds have been experimentally investigated. Pumping by picosecond and nanosecond lasers, respectively, these two compounds possess strong two-photon absorption and optical limiting effects. The results of time-resolved fluorescence of them in DMF solvent at the different concentrations and small quantum yields indicate that the non-radiation process and reabsorption result in the low emission efficiency of these new molecules with large two-photon absorption (TPA) cross-sections.

Synthesis and ab initio X-ray powder diffraction structure of the new alkali and alkali earth metal borate NaCa(BO3).

A sodium calcium borate, NaCaBO3, has been synthesized by the solid-state reaction method and the structure solved from X-ray powder diffraction data. The compound crystallizes in space group Pmmn and has a desired structure type containing isolated planar BO3(3-) anions. Mixed occupancy is found to exist in the Ca site, with partial replacement by Na. One Ca/Na mixed atom and one Na atom are at sites with mm2 symmetry, and a second Ca/Na mixed atom, an Na atom, two B and two O atoms are on mirror planes.

Two-photon absorption spectra of new organic compounds

Abstract Two-photon absorption (TPA) spectra of three organic compounds have been directly measured by an approach of using tunable laser from an optical parameter amplifier as an excitation source. The output intensity of the optical parameter amplifier can cover a broad spectral range 400–2000 nm, and the same intensity in the whole spectral range can be easily adjusted. Therefore, the measurement based on this method is direct and reliable. The experimental results show that the profiles of the TPA spectra are quite similar to those of the linear absorption spectra. All of these compounds exhibit large TPA cross-section in a broad spectral range from 750 to 1100 nm.

Thermal stability and crystal structure of β-Ba3YB3O9

A new compound, beta-Ba3YB3O9, has been attained through solid phase transition from alpha-Ba3YB3O9 at high temperatures. Differential thermal analysis (DTA) revealed the phase transition at about 1120degreesC, the melting temperature at about 1253degreesC. Its crystal structure has been determined from powder X-ray diffraction data. The refinement was carried out using the Rietveld method and the final refinement converged with R-p = 10.5% and R-wp = 13.7%. This compound belongs to the hexagonal space group R-3, with lattice parameters a = 13.0441(1) Angstrom and c = 9.5291(1) Angstrom. There are 6 formulas per unit cell and 7 atoms in the asymmetric unit. The structure of beta-Ba3YB3O9 is built up from Ba(Y)O-8, BaO6 and YB6O18 units formed by one YO6 octahedron and six BO3 triangles with shared O atoms

Illustration of charge transfer in graphene-coated hexagonal ZnO photocatalysts using Kelvin probe force microscopy

A graphene coated hexagonal ZnO (HZO@Gr) with enhanced activity in photocatalysis was synthesized. However, the photoinduced charge transfer behavior and the beneficial role of graphene in promoting photocatalytic reactions have not been sufficiently investigated experimentally. In this paper, the surface potentials of the ±(0001)-polar plane of HZO (Zn-polar plane and O-polar plane), graphene, graphene/Zn-polar plane and graphene/O-polar plane were measured using Kelvin probe force microscopy (KPFM). On the basis of the KPFM results, the respective Fermi levels were calculated and the internal electric field (IEF) of HZO was confirmed. Taking the IEF of HZO into consideration, the three-dimensional band diagrams of the HZO@Gr composites in methyl blue (MB) solution in the dark and under UV-visible irradiation after equilibrium were proposed. Accordingly, it is found that there could emerge different interactions between graphene and HZO at the ±(0001)-polar plane of HZO. Furthermore, the photogenerated holes and electrons tend to migrate to opposite directions. With the participation of graphene and IEF, the composites show a decrease in possibility of charge recombination. As a result, the active groups, namely ˙OH and ˙O2− radicals, could be mainly generated at/near the O-polar plane and Zn-polar plane, respectively. This work can serve as a supplemental explanation of the charge transfer during the photocatalytic process at the polar ZnO/graphene composite surface.

The Study of the Effects of VUV/UV Radiation on the Thermal Control Coatings

In recent years, extensive research has been conducted on long-term reliability of thermal control coatings (TCC) used in space. The properties of TCC’s directly affect the internal temperature control of spacecraft and their normal performance. In this paper, optical properties of several typical TCC samples including the antistatic silvered cerium glass second reflectance mirror, KS-Z white coating, antistatic F46 film silvered second reflectance mirror were measured in situ in different VUV (115–200 nm) and UV (200–400 nm) ranges and radiation doses using a long-term ultraviolet radiation exposure facility. Data fitting was conducted to obtain the solar absorption ratio degradation curve of the thermal control coatings, and the ratio was extrapolated reasonably. The solar absorption ratio of the thermal control coatings tends stabilize after a certain amount of radiation, whether UV or VUV. Other parameters of the thermal control coatings before and after UV/VUV radiation, such as the surface microstructure and infrared emissivity were also measured and their degradation after UV/VUV radiation is discussed.