Browsing by Author "Lee, Chi-Shen"

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A Novel Tunable Green- to Yellow-Emitting beta-YFS:Ce(3+) Phosphor for Solid-State Lighting
(2011-08-01)
Wu, Yun-Chen
;
Wang, De-Yin
;
Chen, Teng-Ming
;
Lee, Chi-Shen
;
Chen, Kuo-Ju
A Ce(3+)-activated fluorosulfide phosphor (beta-YFS: Ce(3+)) was synthesized by solid-state reaction in a sealed tube. The crystal structure has been refined from the XRD profiles and there are two different crystallographic rare earth sites, namely, Y(1) and Y(2), where the Ce(3+) ions occupied. The emission band with a maximum at 495 nm of beta-Y(0.99)Ce(0.01) FS phosphor was characterized by the 4f-5d transitions of Ce(3+) ion. With increasing Ce(3+) concentration, the emission variations were observed from 495 to 547 nm. When beta-YFS:Ce(3+) phosphors were utilized to incorporate with n-UV/blue chip, greenish-white light with color rendering index of 65-77 were obtained. The results indicate that the tunable green- to yellow-emitting beta-YFS:Ce(3+) can serve as a potential phosphor for incorporation in fabrication for solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, thermal-quenching behavior, and related LED device data are also presented.
A Novel Tunable Green- to Yellow-Emitting beta-YFS:Ce3+ Phosphor for Solid-State Lighting
(2011-08-01)
Wu, Yun-Chen
;
Wang, De-Yin
;
Chen, Teng-Ming
;
Lee, Chi-Shen
;
Chen, Kuo-Ju
A Ce3+-activated fluorosulfide phosphor (beta-YFS: Ce3+) was synthesized by solid-state reaction in a sealed tube. The crystal structure has been refined from the XRD profiles and there are two different crystallographic rare earth sites, namely, Y(1) and Y(2), where the Ce3+ ions occupied. The emission band with a maximum at 495 nm of beta-Y0.99Ce0.01 FS phosphor was characterized by the 4f-5d transitions of Ce3+ ion. With increasing Ce3+ concentration, the emission variations were observed from 495 to 547 nm. When beta-YFS:Ce3+ phosphors were utilized to incorporate with n-UV/blue chip, greenish-white light with color rendering index of 65-77 were obtained. The results indicate that the tunable green- to yellow-emitting beta-YFS:Ce3+ can serve as a potential phosphor for incorporation in fabrication for solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, thermal-quenching behavior, and related LED device data are also presented.
A quaternary germanium(II) phosphate, Na[Ge-4(PO4)(3)]
(2008-03-01)
Lee, Chi-Shen
;
Weng, Sheng-Feng
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
A new germanium(II) phosphate, sodium tetragermanium tris( phosphate), Na[Ge-4(PO4)(3)], has been synthesized by a solid-state reaction. The compound is isotypic with [Sn-4(PO4)(3)] (A=Na, K, NH4). It features a [Ge-4(PO4)(3)](-) framework made up of GeO3 pyramids and PO4 tetrahedra, which are linked by shared corners, yielding a three-dimensional structure. The crystal studied showed partial inversion twinning.
alpha-(Y,Gd)FS:Ce(3+): a novel red-emitting fluorosulfide phosphor for solid-state lighting
(2011-01-01)
Wu, Yun-Chen
;
Chen, Yi-Chin
;
Wang, De-Yin
;
Lee, Chi-Shen
;
Sun, Ching-Cherng
A novel Ce(3+)-doped fluorosulfide phosphor, alpha-(Y,Gd)FS:Ce(3+), was first investigated as a new candidate for application in phosphor-converted light emitting diodes (LEDs) and thin-film electroluminescence (TFEL) devices. The detailed crystal structure was investigated based on X-ray diffraction profiles using Rietveld refinement methods. This phosphor shows good absorption ranging from ultraviolet to visible region and broad saturated red emission, which can be tuned from 660 to 672 nm, and the photoluminescence (PL) intensity was demonstrated to be effectively enhanced by Gd(3+) substitution.
alpha-(Y,Gd)FS:Ce3+: a novel red-emitting fluorosulfide phosphor for solid-state lighting
(2011-01-01)
Wu, Yun-Chen
;
Chen, Yi-Chin
;
Wang, De-Yin
;
Lee, Chi-Shen
;
Sun, Ching-Cherng
A novel Ce3+-doped fluorosulfide phosphor, alpha-(Y,Gd)FS:Ce3+, was first investigated as a new candidate for application in phosphor-converted light emitting diodes (LEDs) and thin-film electroluminescence (TFEL) devices. The detailed crystal structure was investigated based on X-ray diffraction profiles using Rietveld refinement methods. This phosphor shows good absorption ranging from ultraviolet to visible region and broad saturated red emission, which can be tuned from 660 to 672 nm, and the photoluminescence (PL) intensity was demonstrated to be effectively enhanced by Gd3+ substitution.
alpha-MoO(3) nanocrystals of controlled size on a glass substrate
(2009-03-05)
Wu, Ming-Cheng
;
Lee, Chi-Shen
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
A procedure to grow alpha-MoO(3) nanocrystals of rod and belt forms under mild conditions involved deposition onto a glass substrate via vapor transport with a water-soluble precursor. Scanning electron and transmission electron microscopic studies, selected-area electron diffraction and powder X-ray analyses indicate that these alpha-MoO(3) nanocrystals exhibit rod or belt forms that grow along [0 0 1] and became vertically aligned on the glass substrate. Such deposition is effective to form thin films of controllable size and density of coverage on varying the precursor concentration and the duration of deposition. (C) 2008 Published by Elsevier Ltd.
alpha-MoO3 nanocrystals of controlled size on a glass substrate
(2009-03-05)
Wu, Ming-Cheng
;
Lee, Chi-Shen
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
A procedure to grow alpha-MoO3 nanocrystals of rod and belt forms under mild conditions involved deposition onto a glass substrate via vapor transport with a water-soluble precursor. Scanning electron and transmission electron microscopic studies, selected-area electron diffraction and powder X-ray analyses indicate that these alpha-MoO3 nanocrystals exhibit rod or belt forms that grow along [0 0 1] and became vertically aligned on the glass substrate. Such deposition is effective to form thin films of controllable size and density of coverage on varying the precursor concentration and the duration of deposition. (C) 2008 Published by Elsevier Ltd.
Autothermal steam reforming of ethanol over La2Ce2-xRuxO7 (x=0-0.35) catalyst for hydrogen production
(2013-05-02)
Weng, Sheng-Feng
;
Wang, Yun-Hsin
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
Pyrochlore phases solid solutions, La2Ce2-xRuxO7 (x=0-0.35) were prepared with a sol-gel process and used as catalysts for the autothermal steam reforming of ethanol. The samples as prepared were characterized with powder X-ray diffraction (PXRD), X-ray photoelectron spectra (XPS), and temperature-programmed reduction (TPR). The XPS and TPR spectra revealed the effect of doped Run+ to oxidation states of La and Ce sites. The low temperature reduction ability and relative concentration of Ce4+ ions are increased as the cell-dimension decreased. Tests of catalytic activity showed that the reforming performance of La2Ce2-xRuxO7 catalysts was affected by the Ru/Ce loading ratio. For all catalysts, partial oxidation was favored at a large C/O composition; incomplete ethanol conversion was observed for C/O >= 0.7. The optimized catalyst was La2Ce1.8Ru0.2O7 with hydrogen production rate (r(H2)) 2.01 x 10(-3) mol s(-1) g(cat)(-1) (autothermal temperature similar to 600 degrees C and 97% ethanol conversion at C/O=0.6). The catalyst exhibited stable r(H2) over 26 h of the reaction with ethanol conversion >95%. r(H2) of the catalyst gradually decreased thereafter because LaAlO3 started to formed and affected catalytic process. For the catalyst, the Ru ions remained well dispersed before and after the AESR reaction. (C) 2013 Elsevier B.V. All rights reserved.
Ba3TM2Se9 (TM = Nb, Ta): Synthesis and Characterization of New Polyselenides
(2014-01-06)
Chung, Ming-Yan
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
New ternary polyselenides Ba3TM2Se9 (TM = Nb, Ta) were synthesized through a solid-state reaction, and their structures were characterized using single-crystal X-ray diffraction. These compounds crystallized into a new structural type with a monoclinic space group P2(1)/c. The structures were constructed from distorted, close-packed layers of (3)(infinity)[BaSe3](3.33-) that incorporated TM atoms at octahedral sites and contained [(TM5+)(2)(Se2-)(7)(Se-2(2-))] units. Diffuse reflectance spectra and electronic resistivity measurements indicated semiconducting properties and optical band gaps of 1.3 eV for Ba3Nb2Se9 and 1.6 eV for Ba3Ta2Se9. Raman spectra were used to investigate the interatomic interactions. Calculations of the electronic structure verified the semiconducting behavior and bonding interaction of short Se-Se contacts.
Characterization and electrochemical properties of chromium-substituted pyrochlore Y2Ti2-x Cr (x) O7-delta
(2015-11-01)
Hao, Chia-Kan
;
Hung, Hao-En
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
Pyrochlore oxides Y2Ti2-x Cr (x) O7-delta have been investigated as electrolyte for solid oxide fuel cell. The as-prepared powder was synthesized by sol-gel method and characterized by powder X-ray diffraction, scanning electron microscope/energy-dispersive spectroscopy, inductively coupled plasma atomic emission spectroscopy, temperature-programmed reduction and AC impedance. Y2Ti2-x Cr (x) O7-delta existed in single phase in a range of 0 < x a parts per thousand currency sign 0.8, and the cell parameters decreased as the amount of Cr dopant increased. XPS analyses indicate that the average oxidation state of Cr (n+) ions decreased with the increased Cr content. Measurements of ionic conductivities induced that the optimized performance was observed at x = 0.2 with 0.01 S/cm at 700 A degrees C due to an optimized condition of carrier concentration and carrier mobility. Y2Ti2-x Cr (x) O7-delta existed in single phase in a range of 0 < x a parts per thousand currency sign 0.8 and the optimized performance of ionic conductivity was observed at x = 0.2 with 0.01 S/cm at 700 A degrees C. [GRAPHICS] .
Color-Tunable Fluorosulfide Phosphors for Solid-State Lighting: Structure and Luminescence Investigations
(2011)
Wu, Yun-Chen
;
Chen, Yi-Chin
;
Lee, Chi-Shen
;
Chen, Teng-Ming
;
應用化學系
A novel Y-2(Ca,Sr)F4S2:Ce3+ fluorosuffide phosphor, was synthesized and its crystal structure was refined with Rietveld method. Y-2(Ca,Sr)F4S2:Ce3+ can be efficiently excited by blue light and shows yellow-to-orange broadband emission at 553-590 nm. Possible mechanism of the tunable luminescence properties was explained on the basis of the band structure calculations.
Controlled growth of beta-Na0.24V2O5 nanowire thin films
(2012-10-01)
Ke, Jhih-Syuan
;
Wu, Ming-Cheng
;
Weng, Sheng-Feng
;
Lee, Chi-Shen
;
應用化學系
A method to prepare well-aligned beta-Na0.24V2O5 nanowires (NWs) involves the deposition of a vanadium oxide complex onto a substrate via gaseous transport, followed by a reaction between the complex and a sodium cation (Na+) precursor coated on the substrate. Techniques to investigate the composition, crystallinity, and morphology of products as prepared include ICP-AES, X-ray powder diffraction (PXRD), SEM/transmission electron microscope (TEM), and XPS. PXRD patterns and images from a TEM confirm the single-crystalline nature of beta-Na0.24V2O5 NWs, which grow along direction [1 0 0]. Factors affecting the amount of deposited material and morphology were tested. On varying the reaction conditions, the length of the beta-Na0.24V2O5 wires is controlled in a range of 5-25 mu m. A mechanism of formation is proposed. According to measurements of field emission, the turn-on field is 7.8 V/mu m, and the maximum emission current density of 4.66 mA/cm(2) occurs at field 11 V/mu m. This method is applicable to grow other tertiary metal oxide nanostructures on glass substrate.
Controlled synthesis of VO2(R), VO2(B), and V2O3 vanadium-oxide nanowires
(2013-07-01)
Ke, Jhih-Syuan
;
Weng, Sheng-Feng
;
Wu, Ming-Cheng
;
Lee, Chi-Shen
;
應用化學系
Vanadium-oxide nanowires (NWs) V2O5, VO2(R), VO2(B), and V2O3 are deposited on a substrate to study their field-emission properties. V2O5 NWs are prepared by thermal evaporation via vapor transport of a vanadium-oxide complex under mild conditions. Films of VO2 and V2O3 wires are subsequently prepared by reducing V2O5 one-dimensional nanocrystals at 450 degrees C with hydrogen gas. The composition of the flowing H-2/Ar mixture and the duration of reduction are utilized to control the formation of VO2(R) or VO2(B) NWs. The crystallinity and morphology of products as prepared are characterized using several techniques, including powder X-ray diffraction, a scanning electron microscope, and a transmission electron microscope. The field-emission properties of the vanadium-oxide NWs as prepared exhibit a turn-on field of 4.56-7.65 V/mu m and an emission current density up to 3.68-8.36 mA/cm(2). These features indicate that vanadium-oxide NWs have potential FE emitter applications.
Crystal structure characterization, optical and photoluminescent properties of tunable yellow- to orange-emitting Y-2(Ca,Sr)F4S2:Ce3+ phosphors for solid-state lighting
(2012)
Wu, Yun-Chen
;
Chen, Yi-Chin
;
Chen, Teng-Ming
;
Lee, Chi-Shen
;
Chen, Kuo-Ju
In this study, a new efficient Ce3+-doped fluorosulfide phosphor, Y-2(Ca,Sr)F4S2:Ce3+, was obtained by using solid-state methods in a sealed silica ampoule. The synthesized Y-2(Ca,Sr)F4S2:Ce3+ was characterized by powder X-ray diffraction and refined with Rietveld methods. Y-2(Ca,Sr)F4S2:Ce3+ can be excited by blue light (440-470 nm) and shows yellow-to-orange broadband emission peaking at 553-590 nm with a quantum efficiency of 16-31%. Non-radiative transitions between Ce3+ ions in Y2CaF4S2:Ce3+ and Y2SrF4S2:Ce3+ hosts have also been demonstrated to be attributable to dipole-dipole interactions, and the critical distances were calculated to be 18.9 and 19.3 angstrom. The possible mechanism of the tunable luminescence properties was described on the basis of band structure calculations. In addition, a white LED device was fabricated by using Y-2(Ca,Sr)F4S2:Ce3+ phosphor pumped with a 460 nm blue chip. The CRI value and CCT were measured to be 74-85 and 3500-8700 K, respectively, showing promising potential for solid-state lighting.
Direct Synthesis of Zr-Doped Ceria Nanotubes
(2009-04-02)
Chen, Ying-Chen
;
Chen, Kuei-Bo
;
Lee, Chi-Shen
;
Lin, M. C.
;
應用化學系
Zr-doped ceria nanotuhes (Zr(x)Ce(1-x)O(2)) Were obtained in a high yield from a hydrothermal reaction in an aqueous solution of NaOH with Ce(NO(3))(3)center dot 6H(2)O and ZrO(2) powder in a small proportion. The morphology and crystalline structure were characterized with X-ray diffraction, a scanning electron microscope, and a transmission electron microscope. Mechanisms for the growth of Zr-doped ceria nanotubes are proposed based oil the Kirkendall effect, the formation of the tubular structure is strongly dependent oil the precursor. This is the first report of a direct synthesis of cerium-oxide nanotubes in high yield. The surface area of the nanotubes is 76 m/g and their average pore size is similar to 52.2 nm, Catalytic measurements show that the nanotubes as synthesized are active for an oxygen-storage capacity and for ethanol reforming.
Effect of Ti substitution on the electrochemical properties of LaCr1-x Ti (x) O3+0.5x (x=0-0.15)
(2016-05)
Hao, Chia-Kan
;
Tsai, Chia-Fen
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
Perovskite compound LaCr1-x Ti (x) O3+0.5x (x = 0-0.15) was synthesized from an EDTA-chelating precursor solution at T < 800 A degrees C, a temperature lower than that of the conventional solid-state method. Structural properties were determined at room temperature using X-ray powder diffraction and the lattice parameter decreased with increasing proportion of Ti. LaCr1-x Ti (x) O3+0.5x was chemically stable under a H-2 atmosphere at 900 A degrees C. Both electrical and ionic conductivity increased with increasing proportion of doped Ti, indicative of a p-type semiconductor. An Arrhenius-like behavior was observed, and the optimized bulk electrical conductivity was 0.107 S cm(-1) for LaCr0.85Ti0.15O3.075 at 850 A degrees C. X-ray photoelectron spectra indicate that the effect of the concentration of charge carrier on conductivity is closely related to the oxidation states of ions. The maximum power density reaches as high as 210 mW cm(-2) at 800 A degrees C for SOFC with LaCr1-x Ti (x) O3+0.5x (x = 0.15) anode. Ti-substituted perovskite materials LaTi (x) Cr1-x O3+0.5x (x = 0-0.15) show enhanced electronic and ionic conductivity with increasing proportion of doped Ti. [GRAPHICS]
Enhanced catalytic activity of Ce(1-x)M(x)O(2) (M = Ti, Zr, and Hf) solid solution with controlled morphologies
(2010-01-01)
Chen, Wei-Ta
;
Chen, Kuei-Bo
;
Wang, Ming-Fang
;
Weng, Sheng-Feng
;
Lee, Chi-Shen
Ce(1-x)M(x)O(2) (M = Ti, Zr, and Hf) nanomaterials with controlled morphology and composition were synthesized by a two-step route for the first time. These nanomaterials exhibit high activities for hydrogen reduction and ethanol reforming reactions, and therefore, they may be useful for applications in catalysis and solid oxide fuel cells.
Enhanced catalytic activity of Ce1-xMxO2 (M = Ti, Zr, and Hf) solid solution with controlled morphologies
(2010-01-01)
Chen, Wei-Ta
;
Chen, Kuei-Bo
;
Wang, Ming-Fang
;
Weng, Sheng-Feng
;
Lee, Chi-Shen
Ce1-xMxO2 (M = Ti, Zr, and Hf) nanomaterials with controlled morphology and composition were synthesized by a two-step route for the first time. These nanomaterials exhibit high activities for hydrogen reduction and ethanol reforming reactions, and therefore, they may be useful for applications in catalysis and solid oxide fuel cells.
Experimental and theoretical studies of Sn(3-delta)Pb(delta)Bi(2)Se(6) (delta=0.0-0.7)
(2010-04-01)
Chen, Kuei-Bo
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
New ternary and quaternary chalcogenides, Sn(3-delta)Pb(delta)Bi(2)Se(5) (delta=0.0-0.7), were synthesized from pure elements using the solid-state method. Their crystal structures, determined using single crystal X-ray diffraction, belong to the orthorhombic space group Pnma (No. 62). The structure is related to Pb(3)Bi(2)S(6), which contains NaCl [311] layer units and zigzag arrays of metal atoms along the c-axis. A correlation between the Pb composition and the shifted position of a metal site was observed. Band structure calculations confirmed that the structure is stabilized when the position of the M5 site is farther from the mirror plane. Thermopower and conductivity measurements indicated that all of the compounds are n-type semiconductors with small band gaps. (C) 2010 Elsevier Inc. All rights reserved.
Experimental and theoretical studies of Sn3-delta Pb delta Bi2Se6 (delta=0.0-0.7)
(2010-04-01)
Chen, Kuei-Bo
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
New ternary and quaternary chalcogenides, Sn3-delta Pb delta Bi2Se5 (delta=0.0-0.7), were synthesized from pure elements using the solid-state method. Their crystal structures, determined using single crystal X-ray diffraction, belong to the orthorhombic space group Pnma (No. 62). The structure is related to Pb3Bi2S6, which contains NaCl [311] layer units and zigzag arrays of metal atoms along the c-axis. A correlation between the Pb composition and the shifted position of a metal site was observed. Band structure calculations confirmed that the structure is stabilized when the position of the M5 site is farther from the mirror plane. Thermopower and conductivity measurements indicated that all of the compounds are n-type semiconductors with small band gaps. (C) 2010 Elsevier Inc. All rights reserved.