Materials Science Forum Vols. 663-665

Abstract: Two-color emission phosphors BaGd2(MoO4)4: Eu3+, Er3+, Yb3+ have been synthesized by the high temperature solid-state method. The as-prepared BaGd2(MoO4)4: Eu3+, Er3+, Yb3+ phosphors can emit intense red light under 395 nm UV excitation, while it will show bright green light upon 980 nm infrared light excitation. It is found that the red emission peaks at 595 and 614 nm should be attributed to 5D0-7F1 and 5D0-7F2 transitions of Eu3+, respectively. The green emission peaks centered at 532 and 553 nm under 980 nm excitation, are attributed to Er3+ transitions from 4H11/2 -4I15/2 and 4S3/2-4I15/2, respectively.

Abstract: Novel polyurethane (PU) conducting films consisting of hydroxyl-terminated polybutadienes (HTPB) and carboxyl functionalized multi-walled carbon nanotubes (MWNTs-COOH) were developed by a simple coupling approach based on hydrogen bonding interactions between MWNTs-COOH and PU moieties. The morphologies and structural characterization were conducted by means of FTIR, TEM and TGA etc; and the influence of the MWNTs-COOH loading and curing temperature on vapor response was investigated. The experimental results indicated that a micro-phase separation structure between soft and hard segments was formed, and MWNTs-COOH was tightly encapsulated by PU moieties and homogeneously dispersed in the PUs. The developed films displayed selective response to non-polar organic solvent vapor and good long-term stability.

Abstract: We have investigated the optical absorption and photoluminescence (PL) of a classical banana-shaped liquid crystal, 1,3-phenylene-bis[4-(4'-nonyloxy)phenyliminomethyl]benzoate, in dilute solutions of tetrahydrofuran. Upon the 325 nm excitation from a helium-cadmium laser, the dilute tetrahydrofuran solutions of the banana-shaped compound gives off strong PL with its peak located at about 380 nm (3.26 eV). Interestingly the PL spectrum of the banana-shaped compound has a long tail that extends beyond 500 nm. In order to explore the origin of the PL, we have calculated the electronic structures of the three chromophores in the banana-shaped compound: the central benzene ring (chromophore A), the carbonyl linkage (chromophore B), and the Schiff base bridged two benzene rings in the branched arms of the molecule (chromophore C). Our results have shown that chromophore C is responsible for the 380 nm PL band where the chromophore B is responsible for the long tail in the recorded PL.

Abstract: A series of MF2:Yb3+/Tm3+(M=Ca, Sr, Ba) upconverted nanocrystals were synthesized by hydrothermal method. Polyvinylpyrrolidone(PVP) is an surfactant which can render the nanocrystals dispersible in water and ethanol. Upconverted emission was also detected in the red and NIR regions of the spectrum and assigned to the 1G4-3F4 (centered at 650 nm) and 3H4 -3H6 (centered at 800 nm) transitions, respectively. In addition, MF2:Yb3+/Tm3+ NCs show bright blue upconverted emission under the 980 nm excitation. As-synthesized MF2:Yb3+/Tm3+ luminescent NCs might find some potential applications in areas of photoluminescence and displays

Abstract: The high absorption characteristics, the complex mechanism and the great potential application in detectors of micro-structural material aroused extensive attention. In order to understand the impact of the micro-structure, the optical simulation method based on Monte Carlo is used for reflection characteristics of micro-structural material with the cell of pyramid construction. In this simulation, the body material is made of gold, which can avoid the effect of tranmittance, with a number of 400 cells. The bottom square of each structure is 50×50 µm, and the height of cells is adjustable. Then the relationship between the height and reflectance can be built up. However, a very complex relationship between the reflectance and the input parameters, including refractive index, extinction coefficient and the structure of the material is showed from simulation result. Generally, the reflectance decreases while the height increases.

Abstract: The nonlinear optical susceptibility with inter-subband transitions between conduction band and valence band is theoretically calculated for CdSe/ZnS core-shell quantum dot (QD). Under the effective-mass approximation, the eigenenergy and wavefunction of electrons and holes have been calculated by solving stationary Schrödinger equation. The third-order nonlinear optical susceptibilities χ(3) of quadratic electro-optic effects (QEOE) have been also calculated in the case that spin-orbit splitting is considered.

Abstract: YVO4:Eu3+,Ln (Ln = Bi3+, La3+, Li+) red phosphors were prepared by combustion synthesis, and effect of the Bi3+, La3+, Li+ doping ions on luminescence properties was studied. After doping with Bi3+, the emission intensity, excited by 322nm UV, decreased, but the absorption at 365nm was effectively enhanced; the brightness was increased by doping with La3+ or Li+, and the emission intensity at 619nm for YVO4:0.05Eu3+,0.15 Li+, excitation at 322nm, was about 160% of that for YVO4:0.05Eu3+.

Abstract: Semiconducting Mg2Si films were fabricated on Si (111) substrates by magnetron sputtering and subsequent annealing, and the effects of sputtering pressure on the Mg2Si film growth were studied. The structural and morphological properties of Mg2Si films were investigated by the means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the Mg2Si (220) main diffraction peak intensity increased and then decreased with the increasing of sputtering pressure. The (220) diffraction peak got its maximum at 3.0 Pa sputtering pressure. The intensity of Mg2Si (200) and (400) diffraction peaks increased rapidly as the sputtering pressure decreased when the pressure was lower than 1.5 Pa. The films prepared at higher sputtering pressure had very irregular microstructures, and the surface of semiconducting Mg2Si films became smoother with the decreasing of the sputtering pressure.

Abstract: The M1.99MgSi2O7: Ce3+0.01 (M: Ba, Sr, Ca) phosphors were prepared by the solid-state reaction method. All the samples emit the violet-ultraviolet light with a broad emission band from about 330 nm to 500 nm. All the phosphors samples show a long afterglow. The strongest afterglow intensity and the longest decay duration of the afterglow come from the Ca1.99MgSi2O7: Ce3+0.01 sample. It is attributed to the suitable trap depth and the high trap concentration of this sample. The traps of these phosphors are induced by the lattice defects. A suitable model involving the cation vacancies and the oxygen vacancies, which act as the hole traps and the electron traps respectively, is proposed.

Abstract: The Y3Al5O12: Tb3+ phosphors are synthesized by solid-state reaction method using fluxes of LiF, NaF, MgF2, AlF3, CaF2, SrF3, KH2PO4 and complex fluxes of LiF+AlF3, KH2PO4+LiF separately. The influence of fluxes on phosphors morphology and luminescent properties are investigated by SEM, HITACHI F-450 photometer and cathodoluminescent photometer. The results indicate that KH2PO4 can improve the morphology characteristics of the phosphors, but LiF, AlF3, NaF, MgF2, SrF3, CaF2 are unavailable. LiF, NaF, AlF3, KH2PO4 can improve the phosphors photoluminescent intensity more than 20 percent and cathodoluminescent intensity more than 10 percent. Using KH2PO4 as flux, excellent luminescent properties and well dispersed ~2 m spherical or sub-spherical YAG: Tb3+ phosphors can be synthesized under 1500 oC.