Browsing by Author "Huang, Tung-Ching"

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Destruction of the short-range disorder due to erbium doping in Pb(0.8)La(0.2)TiO(3)films
(2010-05-01)
Huang, Tung-Ching
;
Hsieh, Wen-Feng
;
光電工程學系
;
Department of Photonics
We show the destruction of a displacement of Ti in the short-range structure by observing the disappearance of emission and Raman signals when the Er(3+) concentration exceeds 7 mol% in sol-gel-derived Pb(0.8)La(0.2)TiO(3) polycrystalline films. It is believed that there always exists disorder due to displacement of B ions in the skeleton of BO(6) in perovskite ABO(3) materials. This disorder due to the displacement of Ti ions breaks the center of symmetry to activate emission of rare-earth ions such as Er(3+) and Raman modes of perovskites. We found that the breaking of symmetry can be diminished by introducing more Er(3+) ions. Copyright (C) 2009 John Wiley & Sons, Ltd.
Er-Yb Codoped Ferroelectrics for Controlling Visible Upconversion Emissions
(2009-05-01)
Huang, Tung-Ching
;
Hsieh, Wen-Feng
;
光電工程學系
;
Department of Photonics
Under a 980 nm laser pumping, quenching of green upconversion (UC) emission accompanied with enhancement of red UC emission observed was dominated by the energy back-transfer (EBT) process in Er(3+) and Yb(3+) codoped PbTiO(3), BaTiO(3), and SrTiO(3) polycrystalline powders. The efficiency of the EBT process depends not only on Yb(3+) concentration but also on level match of the doped Er(3+) and Yb(3+) ions caused by the crystal fields with different symmetries. Our UC emission spectra and X-ray diffraction confirm that the centrosymmetric crystal field arising from reducing tetragonality causes level match of transition (4)S(3/2) -> (4) I(13/2) of Er(3+) and (2)F(7/2) -> (2) F(5/2) of Yb(3+). This level match is responsible for enhancing red UC emission.
Morphology-Controlled Synthesis of Barium Titanate Nanostructures
(2009-10-05)
Huang, Kuan-Chih
;
Huang, Tung-Ching
;
Hsieh, Wen-Feng
;
光電工程學系
;
Department of Photonics
This study reports the synthesis of morphology-controlled BaTiO(3) nanostructures such as spherical, cube-shaped and rod-shaped BaTiO(3) using a molten-salt synthesis method. This method synthesized products from a reaction of BaO/BaCO(3)(+) and TiO(2) with a eutectic mixture of NaCl-KCl flux at 700 degrees C for 1 h. The experiment used powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy to investigate the structure and morphology of the products. Moreover, the current work also provides a proposed synthetic mechanism of BaTiO(3) in the molten salt to illustrate the in situ transformation mechanism of BaTiO(3) nanostructures in the reaction, The results of the study revealed that the initial shape of the titania and the dissolution rate of the initial precursors critically determine the shapes of the final products.
Size-dependent lattice dynamics of barium titanate nanoparticles
(2007-11-28)
Huang, Tung-Ching
;
Wang, Mei-Tan
;
Sheu, Hwo-Shuenn
;
Hsieh, Wen-Feng
;
光電工程學系
By applying a single-tetragonal-phase model to refine the crystal structure and the coupled-phonon model to analyze transverse optical ( TO) modes of BaTiO3 nanocrystals, we found, upon decreasing the particle size from 140 to 30 nm, that the tetragonality of BaTiO3 nanocrystallites is reduced accompanied by expanding unit-cell volume, which is the dominant mechanism for reducing giant LO-TO splitting in the BaTiO3 system. The weakening coupling of two low-frequency modes among three A(1) ( TO) phonons leads to changing the lowest one from a spectral dip to a peak, whereas the increasing coupling strength between two high-frequency modes repels them farther so that there is less reduction in spectral separation.