Browsing by Author "Chan, Ting-Shan"

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Characterization of magnetic properties of Sr2CuWO6 and Sr2CuMoO6
(2014-04-21)
Vasala, Sami
;
Saadaoui, Hassan
;
Morenzoni, Elvezio
;
Chmaissem, Omar
;
Chan, Ting-Shan
In this work we examine the low-temperature magnetic properties of the two double-perovskite compounds Sr2CuWO6 and Sr2CuMoO6 using magnetic susceptibility, muon spin rotation and relaxation, and neutron powder diffraction measurements. Additionally, the most relevant spin exchange interaction constants are derived from ab initio electronic structure calculations, aided by x-ray absorption spectroscopy. The compounds exhibit quasi-two-dimensional magnetic properties, with broad maxima at T-max = 83 and 95 K for Sr2CuWO6 and Sr2CuMoO6, respectively. However, three-dimensional long-range order takes place below T-N = 24(1) and 28(2) K for Sr2CuWO6 and Sr2CuMoO6, respectively. Our results show that the low-dimensional magnetic correlations are mainly due to the significant next-nearest-neighbor interactions in the ab plane of the double-perovskite structure, whereas three-dimensional long-range magnetic order is caused by weaker next-nearest-neighbor interactions along the c axis. Next-nearest-neighbor interactions are also slightly frustrated by weaker nearest-neighbor interactions within the ab plane. Based on these results we predict the low-temperature magnetic structure in these compounds to be type-II antiferromagnetic order of the double-perovskite lattice.
Characterization of magnetic properties of Sr2CuWO6 and Sr2CuMoO6
(2014-04-21)
Vasala, Sami
;
Saadaoui, Hassan
;
Morenzoni, Elvezio
;
Chmaissem, Omar
;
Chan, Ting-Shan
In this work we examine the low-temperature magnetic properties of the two double-perovskite compounds Sr2CuWO6 and Sr2CuMoO6 using magnetic susceptibility, muon spin rotation and relaxation, and neutron powder diffraction measurements. Additionally, the most relevant spin exchange interaction constants are derived from ab initio electronic structure calculations, aided by x-ray absorption spectroscopy. The compounds exhibit quasi-two-dimensional magnetic properties, with broad maxima at T-max = 83 and 95 K for Sr2CuWO6 and Sr2CuMoO6, respectively. However, three-dimensional long-range order takes place below T-N = 24(1) and 28(2) K for Sr2CuWO6 and Sr2CuMoO6, respectively. Our results show that the low-dimensional magnetic correlations are mainly due to the significant next-nearest-neighbor interactions in the ab plane of the double-perovskite structure, whereas three-dimensional long-range magnetic order is caused by weaker next-nearest-neighbor interactions along the c axis. Next-nearest-neighbor interactions are also slightly frustrated by weaker nearest-neighbor interactions within the ab plane. Based on these results we predict the low-temperature magnetic structure in these compounds to be type-II antiferromagnetic order of the double-perovskite lattice.
Chemical Capture of Phosphine by a Sol-Gel-Derived Cu/TiO(2) Adsorbent - Interaction Mechanisms
(2011-02-10)
Chang, Sue-Min
;
Hsu, Ying-Ya
;
Chan, Ting-Shan
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, a novel sol gel-derived Cu/TiO(2) adsorbent has been demonstrated to exhibit exceptional capacities of 40,62, 49.52, and 108.48 mg PH(3)/g Cu/TiO(2) for the oxidative capture of phosphine (PH(3)) in N(2), air, and humidified air, respectively. We have proposed the oxidative mechanisms for PH(3) on the Cu/TiO(2) sample on the basis of elemental, chemical state, functional group, and microstructural analysis. Moreover, the influence of O(2) and water vapor on the capture capacity is discussed. The transformation of PH(3) followed the sequence of PH(2) -> H(2)P-OH -> HP(OH)(2) -> P(OH)(3) -> HO-P=O -> H(3)PO(4). At the same time, the CuO/Cu(OH)(2) moieties in the TiO(2) lattice were reduced to Cu(0). The H(2)P-OH and HO-P=O are the two stable intermediates, and they occupied the active species to inhibit further chemisorption. Direct oxidation of PH(3) or the intermediates with adsorbed O(2) was not efficient. However, the Cu/TiO(2) sample catalyzed their interactions via reduction and then oxidation of the Cu(2)+ ions. Water vapor acts as a cocatalyst to facilitate the oxidation of the intermediates. The end product, H(3)PO(4), migrated to bound the TiO(2) support and free the CuO/Cu(OH)(2) for the following catalytic processes. Although competitive adsorption of water molecules initially retarded the adsorption rate, the high extent of oxidation greatly promoted the capture capacity of the Cu/TiO(2) in humidified air.
Chemical Capture of Phosphine by a Sol-Gel-Derived Cu/TiO2 Adsorbent - Interaction Mechanisms
(2011-02-10)
Chang, Sue-Min
;
Hsu, Ying-Ya
;
Chan, Ting-Shan
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, a novel sol gel-derived Cu/TiO2 adsorbent has been demonstrated to exhibit exceptional capacities of 40,62, 49.52, and 108.48 mg PH3/g Cu/TiO2 for the oxidative capture of phosphine (PH3) in N-2, air, and humidified air, respectively. We have proposed the oxidative mechanisms for PH3 on the Cu/TiO2 sample on the basis of elemental, chemical state, functional group, and microstructural analysis. Moreover, the influence of O-2 and water vapor on the capture capacity is discussed. The transformation of PH3 followed the sequence of PH2 -> H2P-OH -> HP(OH)(2) -> P(OH)(3) -> HO-P=O -> H3PO4. At the same time, the CuO/Cu(OH)(2) moieties in the TiO2 lattice were reduced to Cu-0. The H2P-OH and HO-P=O are the two stable intermediates, and they occupied the active species to inhibit further chemisorption. Direct oxidation of PH3 or the intermediates with adsorbed O-2 was not efficient. However, the Cu/TiO2 sample catalyzed their interactions via reduction and then oxidation of the Cu-2+ ions. Water vapor acts as a cocatalyst to facilitate the oxidation of the intermediates. The end product, H3PO4, migrated to bound the TiO2 support and free the CuO/Cu(OH)(2) for the following catalytic processes. Although competitive adsorption of water molecules initially retarded the adsorption rate, the high extent of oxidation greatly promoted the capture capacity of the Cu/TiO2 in humidified air.
Composition-driven anionic disorder-order transformations triggered single-Eu2+ -converted high-color-rendering white-light phosphors
(2020-01-15)
Dai, Pengpeng
;
Wang, Qingling
;
Xiang, Mei
;
Chen, Teng-Ming
;
Zhang, Xintong
Single-component, single-activator-converted high-color-rendering index (CRI) white-light phosphors have sparked much interest for phosphor-converted white light-emitting diodes. However, manipulating the distribution and locations of single activators to target desired sites in a given host lattice is still a challenge. Herein, we report the remote regulation of the distribution of Eu2+ ions by engineering and controlling the structural ordering in Sr-3(Ce1-xLax)(PO4)(3):0.05Eu(2+) (SCLP:Eu2+) compound, which are designed by using two-color phosphors with different anionic structural ordering, viz., Sr3Ce(PO4)(3):Eu2+ (yellow) with disordered state of PO4 tetrahedra, and Sr3La(PO4)(3):Eu2+ (blue) with ordered state of PO4 tetrahedra. The successive substitution of Ce by La triggers a pronounced disorder-to-order structural transformation of PO4 tetrahedra within SCLP:Eu2+ compounds and guides remotely the distribution of Eu2+ activators, which is demonstrated by a detailed analysis of synchrotron X-ray diffraction refinement, electron paramagnetic resonance spectra, electron spin-echo envelope modulation spectra, Raman spectra, nuclear magnetic resonance spectra and micro-cathodoluminescence spectrum. Benefitting from the controllable structural ordering transformation, as-prepared samples form a unique disorder-order crystal structure, exhibiting controllable microstructure acting on Eu2+ ions, tunable-color emissions including a high CRI (Ra = 90) white-light, increased structural rigidity and thermal stability. These interesting findings in the local structure-dependent luminescence properties demonstrate that structural ordering engineering may be an effective approach to regulate the migration of Eu2+ activators and improve the thermal stability of phosphors.
Conformal deposition of Pt on titania nanotubes to produce a bio-electrode for neuro-stimulating applications
(2018-03-01)
Wu, Yi-Jia
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Chung, Tsai-Wei
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Huang, Jun-Qian
;
Wu, Pu-Wei
;
Chen, Po-Chun
We develop an alkaline electroless bath for deposition of a conformal Pt layer 40 nm thick on titania nanotubes 800 nm long. The charge storage capacity (CSC) and electrochemically active surface area (ECSA) of this Pt-coated titania nanotube array have been studied to evaluate its potential as a bio-electrode for implantable bioelectronic devices. Images from electron microscopes confirm the formation of a uniform Pt film on both the internal and external surfaces of the nanotubes. The X-ray diffraction pattern indicates a preferred (111) orientation. Analysis from X-ray absorption spectroscopy on the plating bath suggests a reduction sequence of Pt4+ -> Pt2+ -> Pt. The Pt-coated titania nanotube array has large CSC and ECSA values, attributed to the hollow tubular nanostructure with a conformal Pt coating.
Conformal Deposition of RuO2 on Cu via a Galvanic Cementation Reaction
(2019-06-28)
Lin, Chun
;
Chou, Shih-Cheng
;
Tso, Kuang-Chih
;
Hsieh, Yi-Chieh
;
Chan, Ting-Shan
We develop a seedless wet chemical process to deposit uniform RuO2 on a Cu substrate. Our approach entails the synthesis of volatile RuO4 colloids in a pH 9 aqueous solution from the oxidation of RuCl52- by ClO-, followed by a galvanic cementation reaction in which the Cu undergoes a mild oxidation in conjunction with the reduction of RuO4 to produce a dense and conformal RuO2 thin film on the Cu surface. The nature for the chemical reactions and constituents involved are investigated by UV-Vis, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Both as-deposited and annealed RuO2 films are characterized by scanning electron microscope and X-ray diffractometer. The as-deposited RuO2 film, with a thickness of 199 nm, reveals an amorphous structure and after an Ar annealing, becomes crystalline in rutile phase. In between the RuO2 and Cu, there are presence of CuO from the displacement cementation reaction, and Cu2O from the parasitic Cu corrosion as expected from the Pourbaix diagram. These Cu oxides, with a thickness of 330 nm, provide sufficient adhesive bonding between RuO2 and Cu. (c) The Author(s) 2019. Published by ECS.
Crystal structure of blue-white-yellow color-tunable Ca4Si2O7F2:Eu2+,Mn2+ phosphor and investigation of color tunability through energy transfer for single-phase white-light near-ultraviolet LEDs
(2012)
Huang, Chien-Hao
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Chan, Ting-Shan
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Liu, Wei-Ren
;
Wang, De-Yin
;
Chiu, Yi-Chen
The crystal structure of Ca4Si2O7F2:Eu2+,Mn2+ was refined and determined from X-ray diffraction (XRD) profiles obtained using a synchrotron light source by the Rietveld refinement method. It was found to crystallize into a monoclinic structure with the P2(1)/c(14) space group. On examining the Mn2+-concentration-dependent photoluminescence properties, we found that the emission colors could be tuned from blue (0.152, 0.112) to white-light (0.351, 0.332) and eventually to yellow (0.430, 0.423) through energy transfer by changing the Eu2+/Mn2+ ratio. Moreover, energy transfer from a sensitizer Eu2+ to an activator Mn2+ occurs via a resonance-type dipole-quadrupole interaction mechanism, and the critical distances of the energy transfer were calculated to be 11.66 angstrom and 12.61 angstrom using concentration quenching and spectral overlap methods, respectively. Combining a 400 nm near-ultraviolet (NUV) chip and a single-phase white-emitting (Ca0.96Eu0.01Mn0.03)(4)Si2O7F2 phosphor produced a white-light NUV LED with CIE chromaticity coordinates of (0.347, 0.338) and a warm color temperature of 4880 K.
Effects of oxygen partial pressure on structural and gasochromic properties of sputtered VOx thin films
(2013-10-01)
Jang, Wei-Luen
;
Lu, Yang-Ming
;
Lu, Ying-Rui
;
Chen, Chi-Liang
;
Dong, Chung-Li
VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target in an Ar-O-2 gas mixture and pure O-2. For the films deposited in the gas mixture, the Ar flow rate was controlled at 20 sccm and the oxygen flow rate was controlled at 1, 3, and 5 sccm, respectively. A thin (similar to 5 nm) Pt layer was deposited on the VOx thin films as a hydrogen catalyst. The long-range structural order, short-range atom arrangement, and gasochromic properties of the deposited films were studied. The grazing incidence X-ray diffraction (GIXRD) results indicate that the deposited films are amorphous. Lamellar structures were found at oxygen flow rates of 3 sccm and above. The X-ray absorption spectroscopy (XAS) results show that the short-range atom arrangement of the lamellar VOx thin films is similar to that of crystal V2O5. The GIXRD and XAS results show that the film obtained with the gas mixture and at an oxygen flow rate of 1 sccm did not significantly change after exposure to hydrogen, whereas the other films exhibited decreased interlayer distance, oxidation state, and crystallinity. The color of the films changed from light or deep yellow to gray. The results suggest that the gasochromic properties of the VOx thin films are related to the V2O5-like atom arrangement and the interlayer distance of the lamellar structure. The films deposited with an oxygen flow rate of 3 sccm and above can be applied to H-2 gas sensors. (C) 2013 Elsevier B. V. All rights reserved.
Efficacies of dopants in thermoelectric BiOCuSe
(2016-07-01)
Chou, Ta-Lei
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Tewari, Girish C.
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Srivastava, Divya
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Yamamoto, Atsushi
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Chan, Ting-Shan
Moderately-doped BiOCuSe-based materials are actively investigated worldwide as new promising candidates for intermediate-temperature thermoelectric power generation. Here we explain for two differently doped BiOCuSe materials, i.e. Cu-deficient BiOCu1-xSe and Ca-for-Bi substituted (Bi1-yCay) OCuSe systems, the differences in their efficacies to enhance the thermoelectric performance of the pristine BiOCuSe material using theoretical calculations and x-ray absorption spectroscopy (XAS) at various edges. In the Cu-deficient system the doping dominantly induces an oxide layer-to-selenide layer charge transfer process. On the other hand, the Ca-for-Bi substitution not only gives lower electrical resistivity but also better thermal stability thanks to the increased ionic bonding character in the selenide block. Density of states nearby the Fermi level suggests that even though the Bi-Se distance is much longer than the Bi-O bond, its contribution cannot be ruled out. The Se-Bi-O chain contributes to the hole states at the VBM with the Cu 3d - Se 4p antibonding state. (C) 2016 Elsevier B.V. All rights reserved.
Eu2+-Activated Sr8ZnSc(PO4)(7): A Novel Near-Ultraviolet Converting Yellow-Emitting Phosphor for White Light-Emitting Diodes
(2012-12-01)
Huang, Chien-Hao
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Chiu, Yi-Chen
;
Yeh, Yao-Tsung
;
Chan, Ting-Shan
;
Chen, Teng-Ming
The crystal structure of Eu2+-activated Sr8ZnSc(PO4)(7):Eu2+ phosphor was refined and determined from XRD profiles by the Rietveld refinement method using a synchrotron light source. This phosphor crystallizes in the monoclinic structure with the I2/a space group. The SZSP:xEu(2+) phosphors showed a broad yellow emission band centered at 511 and 571 nm depending on the concentration of Eu2+, and the composition-optimized concentration of Eu2+ in the Sr8ZnSc(PO4)(7):Eu2+ phosphor was determined to be 2 mol %. The estimated crystal-field splitting and CIE chromaticity coordinates of Sr8ZnSc(PO4)(7):xEu(2+) (x = 0.001-0.05 mol) were 20181-20983 cm(-1) and (0.3835, 0.5074) to (0.4221, 0.5012), respectively, and the emission band showed a redshift from 547 to 571 nm with increasing Eu2+ concentration. The nonradiative transitions between the Eu2+ ions in the Sr8ZnSc(PO4)(7) host were attributable to dipole-dipole interactions, and the critical distance was approximately 19.8 angstrom. The combination of a 400 nm NUV chip with a blend of Sr8ZnSc(PO4)(7):0.02Eu(2+) and BAM:Eu2+ phosphors (light converters) gave high color rendering indices between 79.38 and 92.88, correlated color temperatures between 4325 and 7937 K, and tuned CIE chromaticity coordinates in the range (0.381, 0.435) to (0.294, 0.310), respectively, depending on the SZSP:0.02Eu(2+)/BAM:Eu2+ weight ratio. These results suggest that the Sr8ZnSc(PO4)(7):0.02Eu(2+)/BAM:Eu2+ phosphor blend has potential applications in white NUV LEDs.
EXAFS study of thermoelectric BiCuOSe: Effects of Cu vacancies
(2015-03-01)
Chou, Ta-Lei
;
Tewari, Girish C.
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Chan, Ting-Shan
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Hsu, Ying-Ya
;
Yamauchi, Hisao
Excellent thermoelectric performance has been reported for the ZrCuSiAs-type BiCuOSe derivatives; for these materials the transport properties can be effectively adjusted by chemical substitutions or by introducing Cu vacancies. In this work we compare stoichiometric BiCuSeO and its Cu-deficient derivative BiCu0.95SeO by utilizing temperature dependent extended X-ray absorption fine structure (EXAFS) measurements. Such a local probe evidences that Cu vacancies make the lattice more ductile and susceptible to temperature variation. (C) 2015 Elsevier Ltd. All rights reserved.
Heterojunction of Zinc Blende/Wurtzite in Zn1-xCdxS Solid Solution for Efficient Solar Hydrogen Generation: X-ray Absorption/Diffraction Approaches
(2015-10-14)
Hsu, Ying-Ya
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Suen, Nian-Tzu
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Chang, Chung-Chieh
;
Hung, Sung-Fu
;
Chen, Chi-Liang
In the past decade, inorganic semiconductors have been successfully demonstrated as light absorbers in efficient solar water splitting to generate chemical fuels. Pseudobinary semiconductors Zn1-xCdxS (0 <= x <= 1) have exhibited a superior photocatalytic reactivity of H-2 production from splitting of water by artificial solar irradiation without any metal catalysts. However, most studies had revealed that the extremely high efficiency with an optimal content of Zn1-xCdxS solid solution was determined as a result of elevating the conduction band minimum (CBM) and the width of bandgap. In addition to corresponding band structure and bandgap, the local crystal structure should be taken into account as well to determine its photocatalytic performance. Herein, we demonstrated the correlations between the photocatalytic activity and structural properties that were first studied through synchrotron X-ray diffraction and X-ray absorption spectroscopy. The crystal structure transformed from zinc blende to coexisted phases of major zinc blende and minor wurtzite phases at a critical point. The heterojunction formed by coexistence of zinc blende and wurtzite phases in the Zn1-xCdxS solid solution can significantly improve the separation and migration of photoinduced electron hole pairs. Besides, X-ray absorption spectra and UV-vis spectra revealed that the bandgap of the Zn0.45Cd0.55S sample extended into the region of visible light because of the incorporation of Cd element in the sample. These results provided a significant progress toward the realization of the photoelectrochemical mechanism in heterojunction between zinc blende and wurtzite phases, which can effectively separate the charge-carriers and further suppress their recombination to enhance the photocatalytic reactivity.
Heterojunction of zinc Blende/Wurtzite in Zn1-xCdxS solid solution for efficient solar hydrogen generation: X-ray absorption/diffraction spectroscopy approach
(2016-03-13)
Hsu, Ying-Ya
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Suen, Nian-Tzu
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Hong, Song-Fu
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Chan, Ting-Shan
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Chen, San-Yuan
Interplay between potassium doping and bandgap profiling in selenized Cu(In,Ga)Se-2 solar cells: A functional CuGa: KF surface precursor layer
(2018-05-01)
Cai, Chung-Hao
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Chen, Rong-Zhi
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Chan, Ting-Shan
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Lu, Ying-Rui
;
Huang, Wei-Chih
The progress of selenized Cu(In,Ga)Se-2 (CIGSe) solar cells is limited by low open-circuit voltage (Voc), which results from the Ga-deficient surface and undesirable bandgap profile after selenization. Controlling the Ga grading, especially on the CIGSe surface, is challenging but critical for further efficiency improvement. Here, the simple sputtering route with K incorporation is presented to engineer single-or double-graded bandgap. The K incorporation through sputtered precursors can considerably affect the Ga profile in CIGSe during selenization, essentially distinct from reported KF post-deposition treatment, in which the Ga profile keeps unchanged. Using synchrotron-based X-ray absorption spectroscopy and first-principle calculations, we verify that Ga diffusion via Cu vacancies is restrained due to the presence of K-Cu defects. Therefore, by introducing a CuGa:KF surface layer on the bi-layer precursors, the surface Ga content of CIGSe is increased effectively, achieving a notch-like Ga distribution after selenization. This unique CuGa: KF layer significantly boosts the Voc and yields over 15% efficiency, even with a low reactive Se vapor for selenization. Our approach, completely compatible with the existing fabrication process, offers a new direction for engineering band structure without sulfurization.
Local geometric and electronic structures of gasochromic VOx films
(2014)
Jang, Wei-Luen
;
Lu, Yang-Ming
;
Chen, Chi-Liang
;
Lu, Ying-Rui
;
Dong, Chung-Li
VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target at room temperature. Local atomic and electronic structures of the films were then modified by thermal annealing. The oxidation state and structural and gasochromic properties of the films were elucidated by X-ray absorption spectroscopy. Analytical results indicate that the as-deposited VOx films were amorphous with mixed V4+ and V5+ valences. The amorphous VOx had a disordered and expanded lamellar structure resembling that of polymer-intercalated V2O5 gels. VOx films were crystallized into orthorhombic V2O5 at 300 degrees C, and the lamellar structure was eliminated at 400 degrees C. Additionally, the gasochromic reaction reduced the vanadium valence via intervalence transitions between V5+ and V3+. Moreover, removing the lamellar structure reduced the gasochromic rate, and the gasochromic reaction transformed the V2O5 crystalline phase irreversibly into an H1.43V2O5 phase. Based on the results of this study, amorphous VOx with a lamellar structure is recommended for use in H-2 gas sensors.
Near UV-pumped yellow-emitting Sr(8)MgSc(PO(4))(7):Eu(2+) phosphor for white-light LEDs with excellent color rendering index
(2011-01-01)
Huang, Chien-Hao
;
Chen, Yen-Chi
;
Chen, Teng-Ming
;
Chan, Ting-Shan
;
Sheu, Hwo-Shuenn
An Eu(2+)-activated Sr(8)MgSc(PO(4))(7):Eu(2+) yellow-emitting phosphor with strong luminescence was synthesized and its crystal structure has been refined and determined from the XRD profiles using synchrotron light source by Rietveld refinement method. Non-radiative transitions between Eu(2+) ions in the Sr(8)MgSc(PO(4))(7) host have also been demonstrated to be attributable to dipole-dipole interactions, and the critical distance was estimated to be 24.83 angstrom by using spectral overlap methods. In addition, white-light near-UV LEDs were fabricated by using a phosphor blend of composition-optimized yellow-emitting Sr(8)MgSc(PO(4))(7):0.01Eu(2+) and blue-emitting BaMgAl(10)O(17):Eu(2+) commodity pumped with a 400 nm near-UV chip and the Ra value and reduced color temperature of were found to be 96.7 and 5,614 K, respectively. These results indicate that yellow-emitting Sr(8)MgSc(PO(4))(7):xEu(2+) can serve as a promising candidate for application in white-light LEDs.
Near UV-pumped yellow-emitting Sr8MgSc(PO4)(7):Eu2+ phosphor for white-light LEDs with excellent color rendering index
(2011-01-01)
Huang, Chien-Hao
;
Chen, Yen-Chi
;
Chen, Teng-Ming
;
Chan, Ting-Shan
;
Sheu, Hwo-Shuenn
An Eu2+-activated Sr8MgSc(PO4)(7):Eu2+ yellow-emitting phosphor with strong luminescence was synthesized and its crystal structure has been refined and determined from the XRD profiles using synchrotron light source by Rietveld refinement method. Non-radiative transitions between Eu2+ ions in the Sr8MgSc(PO4)(7) host have also been demonstrated to be attributable to dipole-dipole interactions, and the critical distance was estimated to be 24.83 angstrom by using spectral overlap methods. In addition, white-light near-UV LEDs were fabricated by using a phosphor blend of composition-optimized yellow-emitting Sr8MgSc(PO4)(7):0.01Eu(2+) and blue-emitting BaMgAl10O17:Eu2+ commodity pumped with a 400 nm near-UV chip and the Ra value and reduced color temperature of were found to be 96.7 and 5,614 K, respectively. These results indicate that yellow-emitting Sr8MgSc(PO4)(7):xEu(2+) can serve as a promising candidate for application in white-light LEDs.
New Ce3+-Activated Thiosilicate Phosphor for LED Lighting-Synthesis, Luminescence Studies, and Applications
(2014-05-28)
Lee, Szu-Ping
;
Huang, Chien-Hao
;
Chan, Ting-Shan
;
Chen, Teng-Ming
;
應用化學系
A new Ce3+-activated thiosilicate phosphor, BaLa2Si2S8:Ce3+, was synthesized by using solid-state methods in a fused silica ampule and found to crystallize in the structure type of La2PbSi2S8. The crystal structure has been characterized by synchrotron X-ray diffraction and refined with Rietveld methods. This novel cyan-emitting phosphor can be excited over a broad range from UV to blue light (380-450 nm) and generates a broadband emission peaking at 471 nm with a quantum efficiency of 36%. Nonradiative transitions between Ce3+ ions in BaLa2Si2S8:Ce3+ have also been demonstrated to be attributable to dipole-dipole interactions, and the critical distance was calculated to be 17.41 angstrom. When BaLa2Si2S8:Ce3+ phosphor was utilized to incorporate with yellow-emitting (Sr,Ca)(2)SiO4:Eu2+ phosphor and red-emitting CaAlSiN3:Eu2+ phosphor on a 430 nm blue LED chip, a warm white light LED device with color rendering index of similar to 96 was obtained. The results indicate that cyan-emitting BaLa2Si2S8:Ce3+ can serve as a potential phosphor for incorporation in fabrication of solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, decay lifetime, thermal-quenching behavior, and related LED device data are also presented.
Ni-Nanocluster Modified Black TiO2 with Dual Active Sites for Selective Photocatalytic CO2 Reduction
(2018-01-11)
Billo, Tadesse
;
Fu, Fang-Yu
;
Raghunath, Putikam
;
Shown, Indrajit
;
Chen, Wei-Fu
One of the key challenges in artificial photosynthesis is to design a photocatalyst that can bind and activate the CO2 molecule with the smallest possible activation energy and produce selective hydrocarbon products. In this contribution, a combined experimental and computational study on Ni-nanocluster loaded black TiO2 (Ni/TiO2[Vo]) with built-in dual active sites for selective photocatalytic CO2 conversion is reported. The findings reveal that the synergistic effects of deliberately induced Ni nanoclusters and oxygen vacancies provide (1) energetically stable CO2 binding sites with the lowest activation energy (0.08 eV), (2) highly reactive sites, (3) a fast electron transfer pathway, and (4) enhanced light harvesting by lowering the bandgap. The Ni/TiO2[Vo] photocatalyst has demonstrated highly selective and enhanced photocatalytic activity of more than 18 times higher solar fuel production than the commercial TiO2 (P-25). An insight into the mechanisms of interfacial charge transfer and product formation is explored.