Browsing by Author "Wu, Pin-Jiun"

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(Ca,Mg,Sr)(9)Y(PO(4))(7):Eu(2+),Mn(2+): Phosphors for white-light near-UV LEDs through crystal field tuning and energy transfer
(2011-01-01)
Huang, Chien-Hao
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Wu, Pin-Jiun
;
Lee, Jyh-Fu
;
Chen, Teng-Ming
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應用化學系
Two series of single-composition (Ca,Mg,Sr)(9)Y(PO(4))(7):Eu(2+) and (Ca(0.5)Sr(0.5))(9)Y(PO(4))(7):Eu(2+),Mn(2+) phosphors were synthesized via high-temperature solid-state reactions. Their emission colors could be tuned from blue to green and eventually to red through tuning the crystal field splitting and energy transfer. On examining the Mn(2+) concentration-dependent photoluminescence properties, we found that co-doping with Mn(2+) would lead to a change in Eu(2+)/Eu(3+) ratio. Moreover, an energy transfer from Eu(2+) to Mn(2+) occurs because of the spectral overlap between the emission band of Eu(2+) and the excitation band of Mn(2+). The resonance-type energy transfer via a dipole-quadrupole interaction mechanism was supported by decay lifetime data and the critical distance of energy transfer was calculated to be 11.09 angstrom A. A trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca(0.5)Sr(0.5))(9)Y (PO(4))(7):0.007Eu(2+),0.02Mn(2+) and blue-emitting (Ca(0.5)Mg(0.5))(9)Y(PO(4))(7):0.007Eu(2+) phosphors into a single package. Such a composite device emitted white light with a correlated color temperature of 6303 K, a color rendering index of 87.4, and color coordinates (0.314, 0.348) close to those of ideal white light. The results suggest that a phosphor blend of (Ca(0.5)Sr(0.5))(9)Y(PO(4))(7):0.007Eu(2+), 0.02Mn(2+) and (Ca(0.5)Mg(0.5))(9)Y(PO(4))(7):0.007Eu(2+) is potentially useful for white n-UV light-emitting diodes (LEDs).
(Ca,Mg,Sr)(9)Y(PO4)(7):Eu2+,Mn2+: Phosphors for white-light near-UV LEDs through crystal field tuning and energy transfer
(2011-01-01)
Huang, Chien-Hao
;
Wu, Pin-Jiun
;
Lee, Jyh-Fu
;
Chen, Teng-Ming
;
應用化學系
Two series of single-composition (Ca,Mg,Sr)(9)Y(PO4)(7):Eu2+ and (Ca0.5Sr0.5)(9)Y(PO4)(7):Eu2+,Mn2+ phosphors were synthesized via high-temperature solid-state reactions. Their emission colors could be tuned from blue to green and eventually to red through tuning the crystal field splitting and energy transfer. On examining the Mn2+ concentration-dependent photoluminescence properties, we found that co-doping with Mn2+ would lead to a change in Eu2+/Eu3+ ratio. Moreover, an energy transfer from Eu2+ to Mn2+ occurs because of the spectral overlap between the emission band of Eu2+ and the excitation band of Mn2+. The resonance-type energy transfer via a dipole-quadrupole interaction mechanism was supported by decay lifetime data and the critical distance of energy transfer was calculated to be 11.09 angstrom A. A trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca0.5Sr0.5)(9)Y (PO4)(7):0.007Eu(2+),0.02Mn(2+) and blue-emitting (Ca0.5Mg0.5)(9)Y(PO4)(7):0.007Eu(2+) phosphors into a single package. Such a composite device emitted white light with a correlated color temperature of 6303 K, a color rendering index of 87.4, and color coordinates (0.314, 0.348) close to those of ideal white light. The results suggest that a phosphor blend of (Ca0.5Sr0.5)(9)Y(PO4)(7):0.007Eu(2+), 0.02Mn(2+) and (Ca0.5Mg0.5)(9)Y(PO4)(7):0.007Eu(2+) is potentially useful for white n-UV light-emitting diodes (LEDs).
CARBON-DOPED TiO2 NANOTUBES: EXPERIMENTAL AND COMPUTATIONAL STUDIES
(2013-05-01)
Huang, Wen-Fei
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Wu, Pin-Jiun
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Hsu, Wei-Chih
;
Wu, Chih-Wei
;
Liang, K. S.
C-doped TiO2 nanotubes (NTs) with anatase structure, prepared by anodizing the polished Ti foils, were characterized using X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and synchrotron-based X-ray photoemission spectroscopy (XPS). XPS results show electron losses in C atoms, no electron change in Ti atoms, and two doping energy levels appeared in band gaps. Structural geometries, DOSs, PDOSs, and Bader charge analyses of C-doped TiO2 anatase are predicted by periodic DFT calculations. Eight doping positions were taken into consideration: two substitutional cases (in oxygen and titanium sites) and six interstitial cases. We found that the interstitial carbon doping type is the most stable one, whereas the substitutional cases are rather unstable. Band-gap modifications can also be found in oxygen substitution, but not in titanium substitution. Both band-gap modification and non-band-gap modification are found in the interstitial carbon doping. In these eight C-doping systems, only the C atom in the oxygen substitution case gains electrons, 1.14 e, and others present electron losses within 0.5-4.00 e. The results of XPS measurements, DOSs calculations, and Bader charge analyses show that carbon interstitial is the most likely doping type for the C-doped TiO2 NTs.
Dependence of the final-state effect on the coupling between a CdSe nanoparticle and its neighbors studied with photoemission spectroscopy
(2007-03-01)
Wu, Pin-Jiun
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Tsuei, Ku-Ding
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Hsieh, Meng-Ting
;
Wei, Kung-Hwa
;
Liang, Keng S.
A simple model based on an electrostatic calculation of the photoemission effect in the final state is used to characterize the energy shift, relative to bulk material, which is dependent on size in the photoemission spectra of organically passivated CdSe nanoparticles (NPs). For trioctylphosphine oxide/hexadecylamine-passivated NPs, the core-level shifts are well described with a model involving a static effect in the final state. After the NPs are treated with pyridine, the energy shifts are smaller; this decrease is ascribed to a dynamic effect in the final state describing a finite lifetime, on a femtosecond scale, of the photohole residing in the NP. This condition is intimately related to the coupling between the NP and metallic substrate and among NPs themselves. For the valence-band edge, an additional effect of the initial state due to quantum confinement is required to elucidate the energy shift. We find that this initial-state shift is smaller than a prediction according to a semiempirical pseudopotential calculation.
Depth-Profiling Electronic and Structural Properties of Cu(In,Ga)(S,Se)(2) Thin-Film Solar Cell
(2016-09-14)
Chiang, Ching-Yu
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Hsiao, Sheng-Wei
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Wu, Pin-Jiun
;
Yang, Chu-Shou
;
Chen, Chia-Hao
Utilizing a scanning photoelectron microscope (SPEM) and grazing-incidence X-ray powder diffraction (GIXRD), we studied the electronic band structure and the crystalline properties of the pentanary Cu(In,Ga)(S,Se)(2) (CIGSSe) thin-film solar cell as a function of sample depth on measuring the thickness-gradient sample. A novel approach is proposed for studying the depth-dependent information on thin films, which can provide a gradient thickness and a wide cross-section of the sample by polishing process. The results exhibit that the CIGSSe absorber layer possesses four distinct stoichiometries. The growth mechanism of this distinctive compositional: distribution formed by a two stage process is described according to the thermodynamic reaction and the manufacturing, process. On the basis of the depth-profiling results, the gradient profiles of the conduction and valence bands were constructed to elucidate the performance of the electrical properties (in this case, V-oc = 620 mV, J(sc) = 34.6 mA/cm(2), and eta = 14.04%); the valence-band maxima (VBM) measured with a SPEM in the spectroscopic mode coincide with this band-structure model, except for a lowering of the VBM observed in the surface region of the absorber layer due to the ordered defect compound (ODC). In addition, the depth-dependent texturing X-ray diffraction pattern presents the crystalline quality and the residual stress for each depth of a thin-film device. We find that the randomly oriented grains in the bottom region of the absorber layer and the different residual stress between the underlying Mo and the absorber interface, which can deteriorate the electrical performance due to peeling-off effect. An anion interstitial defect can be observed on comparing the anion concentration, of the elemental distribution with crystalline composition; a few excess sulfur atoms insert in interstitial sites at the front side of the absorber layer, whereas the interstitial selenium atoms insert at the back side.
Effect of Formation Temperature on Quality of Gate Dielectric on Germanium Substrate
(2016)
Wei, Erh-Jye
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Tsui, Bing-Yue
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Wu, Pin-Jiun
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加速器光源科技與應用學位學程
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電子工程學系及電子研究所
Germanium metal-insulator-semiconductor (MIS) structure with HfO2/Al2O3/GeO2 gate stack have been demonstrated to exhibit good performance. In this work, the effect of formation temperature of the gate stack on the quality of the gate dielectric is investigated. It is found that the higher plasma oxidation temperature helps the GeO2 formation and less interface states. But the higher deposition temperature of the ALD high-k films may degrade the interface and result in higher leakage current.
Energy shift of photoemission spectra for organics-passivated CdSe nanoparticles: The final-state effect
(2007-01-01)
Wu, Pin-Jiun
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Tsuei, Ku-Ding
;
Wei, Kung-Hwa
;
Liang, Keng S.
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材料科學與工程學系
Size-dependent energy shift of photoemission spectra with respect to bulk sample has been examined for colloidally prepared CdSe nanoparticles with a series of particle sizes. The core-level shifts are well described by a theoretical calculation based on a final-state effect model, whereas an additional initial-state effect due to quantum confinement is required to elucidate the valence-band edge shifts. The results indicate that the interaction between the photohole and the dielectric background in the final state has to be considered in photoemission measurements for organics-passivated nanoparticles. The calculated results in the literature appear to overestimate the initial-state effect compared to our experimental observation. (c) 2006 Elsevier Ltd. All rights reserved.
Large Photoresponsivity in the Amorphous-TiO2/SrRuO(3)Heterostructure
(1970-01-01)
Liu, Heng-Jui
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Huang, Chin-Han
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Chen, Cheng-Ying
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Hsiao, Sheng-Wei
;
Chen, You-Sheng
Thin-film heterostructures are effective in enhancing the performance or triggering novel physical phenomena of optoelectronic applications. For example, the epitaxial heterostructures of ultraviolet-light-sensitive TiO(2)with metallic SrRuO(3)can acquire visible-light functionalities using the hot carrier injection mechanism. Therefore, the TiO2/SrRuO(3)heterostructure system has recently attracted increasing interest. Herein, the amorphous-TiO2/SrRuO(3)heterostructure is fabricated and compared to the epitaxial TiO2/SrRuO3. As opposed to the occurrence of the visible-light photovoltaic effect in the epitaxial TiO2/SrRuO3, the amorphous-TiO2/SrRuO(3)heterostructure herein exhibits different optoelectronic functionality, specifically the photoresistor behavior. The amorphous-TiO2/SrRuO(3)heterostructure achieves a photoresponsivity of 6.56 A W(-1)at 1 V. Such a performance is hardly obtained in typical oxide-based photoresistors. The analyses of the crystalline and electronic structures show that it is due to the defect-induced high electron doping in the amorphous TiO(2)with hot carrier injection mechanism. This study discusses the correlation between the hot carrier injection and band diagram, which provides more degrees of freedom in designing potential optoelectronic devices.
Size dependence of tetrahedral bond lengths in CdSe nanocrystals
(2007-04-16)
Wu, Pin-Jiun
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Stetsko, Yuri P.
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Tsuei, Ku-Ding
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Dronyak, Roman
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Liang, Keng S.
The structural characteristics of organically passivated CdSe nanocrystals (NCs) were investigated with x-ray diffraction and extended x-ray absorption fine structure. As the NC size decreases, the axial bond length R-(1) for an atomic tetrahedron extends but the equatorial bond length R-(2) contracts, with a similar tendency of distortion for the lattice parameters of the wurtzite structure. The authors suggest that the observed hexagonal distortion is attributed to the surface stress of the NCs related to the organic passivation effect and the relaxation of atomic positions at the stacking fault interface. (c) 2007 American Institute of Physics.
Vanadium Substitution of LiFePO4 Cathode Materials To Enhance the Capacity of LiFePO4-Based Lithium-Ion Batteries
(2012-11-22)
Chiang, Ching-Yu
;
Su, Hui-Chia
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Wu, Pin-Jiun
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Liu, Heng-Jui
;
Hu, Chih-Wei
The mechanism of enhancing the capacity of the LiFePO4 cathodes in lithium ion batteries by the addition of a small amount of vanadium, which locate on the lithium site and induce lithium vacancies in the crystal structure, is reported in this article. As a result, the capacity increases from 138 mAh/g found for pristine LiFePO4 to 155 mAh/g for the V-added compound, and the conductivity increases from 4.75 x 10(-4) S/cm for the LiFePO4 without V addition to 1.9 x 10(-2) S/cm for the V-added compound. A possible model to facilitate the enhancement of conductivity and capacity is described with evidence supported by X-ray powder diffraction, X-ray absorption spectroscopy, and neutron powder diffraction data.