Lay-Gaik Teoh

Preparation and Photoluminescence Properties of Pr3+ Ion-Doped Ca2LaTaO6 Phosphors

In this study, Pr3+ ion-doped Ca2LaTaO6 phosphors were synthesized using a vibrating milled solid-state reaction with metal oxides and calcined in air at 1100°C for 8xa0h. The crystal structure and photoluminescence properties were also investigated. The x-ray powder diffraction patterns show that all of the peaks can be attributed to monoclinic Ca2LaTaO6 phase with increasing Pr3+ ion doping. The scanning electron microscopy images show that the particles are irregular, with the most uniform distribution being obtained for Pr3+ ion concentration of 3xa0mol.%. The emission spectra of Ca2(La1−xPrx)TaO6 phosphors showed a dominant green emission peak at 490xa0nm under excitation at 451xa0nm, which was due to the 3P0xa0→xa03H4 transition. A series of weak emission peaks at 531xa0nm, 544xa0nm, 615xa0nm, 621xa0nm, and 652xa0nm were assigned to the 3P0xa0→xa03H5, 1D2xa0→xa03H4, 3P0xa0→xa03H6, and 3P0xa0→xa03F2 transitions of Pr3+ ions, respectively. In addition, the emission intensities of the Ca2(La1−x Prx)TaO6 phosphors increased then decreased as the Pr3+ ion concentration was increased, and the maximum emission intensity occurred for x of 0.03, corresponding to an average grain size of 41.5xa0nm with critical distance of 16.32xa0Å. The Commission Internationale de l’Eclairage color chromaticity coordinates for the Ca2LaTaO6:Pr3+ phosphors were all located in the green region, but shifted from (xxa0=xa00.145, yxa0=xa00.463) to (xxa0=xa00.119, yxa0=xa00.471) as the Pr3+ ion concentration was increased from 0.5xa0mol.% to 10xa0mol.%.

Structure and dielectric properties of lower valence compensation for Ba1-xNax(FeTa)0.5O3 by reaction sintering process

ABSTRACT Complex perovskite oxides of Ba1-xNax(FeTa)0.5O3 (BNFT, x = 2, 4, 6, 8, 14, and 20 mole%) dielectric ceramics doped with lower valence compensation ions were prepared by a reaction-sintering process. The BNFT dielectrics were sintered at 1300°C for 8 h without calcinations involved. Due to low melting point of Na2CO3, the sintering temperature of dielectric decreased. The density of sintered dielectrics increased with increasing Na+ ion concentration and it cause BNFT dielectric surface glossy. The relative densities of sintered dielectrics were higher than 89.5%. The dielectric constant of Ba0.96Na0.04(FeTa)0.5O3 1300°C sintered ceramic was about 9 × 105, measured at room temperature at frequency of 1 kHz. The temperature-dependent loss curves measured in temperature range of −15∼90°C and frequency of 1 k∼1 MHz indicated that the samples exhibit a typical relaxor behavior with a broad temperature range which was contributed by orientation and space charge polarization.

Structure and Photoluminescent Properties of B3+-Doped (Y0.9Dy0.1)InGe2O7 Phosphor

A color-tunable, near-white-light-emitting, B3+-doped (Y0.9Dy0.1)InGe2O7 phosphor was synthesized using a solid-state reaction, and its structure and luminescent properties were determined. X-ray powder diffraction patterns showed that all of the diffraction peaks can be attributed to the monoclinic YInGe2O7 crystal structure for B3+ ion concentration up to 5xa0mol.%, and that the optimal concentration for B3+ doping is 3xa0mol.%. In the photoluminescent studies, increasing the B3+ ion concentration caused the intensities of both the excitation and emission peaks to increase and then decrease. In addition, the color tone changes gradually, from the near-white-light region, through greenish, and finally to yellowish. This change is caused by a decrease in the symmetry of the local structure around the Dy3+ ion when the B3+ ion in the host reaches the optimum concentration for the H3BO3 flux of 3xa0mol.%. When the B3+ content is increased further, the distinct difference in ionic radius between the lattice atoms and the substituent atoms causes the lattice to become distorted and the crystallinity of the (Y0.9Dy0.1)InGe2O7 phosphor to decrease.