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1
Content available remote Improved efficiency of dye-sensitized solar cells by doping of strontium aluminate phosphor in TiO2 photoelectrode
Hwangbo S., Kim J. T., Hwang K. S.
Materials Science Poland
|
2015
|
Vol. 33, No. 2
237--241
EN
SrAl2O4:Eu2+, Dy3+ phosphor was synthesized by chemical solution route to use as a dopant in TiO2 layer employed as a photoelectrode for down conversion of ultraviolet and near-ultraviolet to visible and near-infrared light in a dye-sensitized solar cell. Nano-crystalline structure of the SrAl2O4:Eu2+, Dy3+powder was confirmed by X-ray diffraction analysis and field emission scanning electron microscopy. Monitored at 520 nm, SrAl2O4:Eu2+, Dy3+ phosphor showed emission peaks at 460 to 610 nm due to 4f6 → 4f7 transitions of Eu2+ ions. For the study, SrAl2O4:Eu2+, Dy3+ phosphor-doped TiO2 layer was deposited on fluorine-doped tin oxide coated glass by electrostatic spray deposition. The short circuit current, open circuit voltage, fill factor, and conversion efficiency of the cells were measured. Experimental results revealed that the device efficiency for the SrAl2O4:Eu2+, Dy3+ phosphor-doped TiO2 layer increased to 7.20 %, whereas that of the pure-TiO2 photoelectrode was 4.13 %.
2
Content available remote Chemical solution-derived SrMg2(PO4)2:Eu2+ blue phosphor for ultraviolet emitting diodes
Hwang K. S., Hwangbo S., Kim J. T.
Optica Applicata
|
2010
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Vol. 40, nr 4
943--948
EN
Eu2+-doped SrMg2(PO4)2 phosphor with blue emission was prepared by the low temperature chemical solution process using inorganic salts as a starting material. Transparent sol was preheated at 300 °C for 120 min and then precursor was finally annealed at 900 °C for 240 min in a reducing CO atmosphere. Crystallinity, surface morphology and luminescent properties have been investigated. The phosphor emits bright blue luminescence with a peak wavelength at 423 nm under near-ultraviolet excitation at 363 nm.
3
Content available remote Red-emitting LiEuW2O8 phosphor for white emitting diodes prepared by sol-gel process
Hwang K. S., Jeon Y. S., Hwangbo S., Kim J. T.
Optica Applicata
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2009
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Vol. 39, nr 2
375-382
EN
Scheelite-type LiEuW2O8 (LEW) phosphors with the optical function of color conversion from near-UV to red were prepared by sol-gel method using a lithium acetate dehydrate, europium(III) nitrate pentahydrate, and tungsten(VI) chloride as starting materials. Viscous mixing sol was prefired at 300 °C for 120 min in air and then white powder precursor was finally annealed at 500-800 °C for 240 min in Ar. From an X-ray diffraction analysis, all the samples are isostructural and belong to the tetragonal system of scheelite-type. The main emission peak is 5D0 › 7F2 transitions of Eu3+ at 615 nm, other transitions from the 5D0 › 7F1, 5D0 › 7F3 and 5D0 › 7F4 located at 570-700 nm range are weak. The characteristic emission of WO4-2 in LEW is quenched absolutely and only red-light emission of Eu3+ appears. Crystallinity, surface properties and red-emission by near-ultraviolet (395 nm) were improved by high-temperature annealing.
4
Content available remote The influence of the prefiring temperature on the structure and surface morphology of sol-gel derived ZnO film
Hwang K. S., Hwangbo S., Kim J. T.
Materials Science Poland
|
2009
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Vol. 27, No. 1
159--170
EN
Show aC-axis oriented ZnO thin films were prepared on silica glass substrates by the sol-gel method using a zinc naphthenate precursor. As-deposited films were prefired at 250 °C for 60 min, at 350 °C for 30 min, and at 500 °C for 10 min, followed by final annealing at 600-900 °C in air. Crystal structure, surface morphology, surface roughness and transmittance at the visible range were analyzed by high resolution X-ray diffraction, field emission scanning electron microscopy, scanning probe microscopy, and ultraviolet spectrophotometry. (002)-oriented ZnO films were obtained by annealing at 600 °C, and at higher temperatures for the films prefired at 350 °C and 500 °C. All the films exhibited a high transmittance, above 80%, in the visible region, and showed a sharp fundamental absorption edge at 0.38-0.40 žm. The most highly c-axis oriented ZnO with a homogeneous surface was observed at a prefiring temperature of 350 °C.
5
Content available remote Effect of prefiring temperature on the texture and optical property of Bi4Ti3O12/MgO(100) prepared by using a metal naphthenate precursor
Hwangbo S., Hwang K. S., Kim J. T.
Optica Applicata
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2008
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Vol. 38, nr 4
635-641
EN
The effect of prefiring temperature on the crystal structure and optical property of the Bi4Ti3O12 films on MgO substrates by using a metal naphthenate precursor was investigated. As-deposited films were prefired at 300 °C, 400 °C and 500 °C for 10 min, followed by annealing at 750 °C for 30 min. According to the pole-figure analysis, texture of the annealed films was found to depend on prefiring temperature. Transmittance and the variation of band gap with prefiring temperature were studied.
6
Content available remote Preparation of lithium zirconate nanopowder prepared by electrostatic spraying for CO2 sorbent
Hwang K. S., Lee Y. H., Hwangbo S.
Materials Science Poland
|
2007
|
Vol. 25, No. 4
969--975
EN
Electrostatic spray pyrolysis has been used to prepare Li2ZrO3 nanopowder for CO2 sorbent. Final annealing was done at 900 st.C for 30 min in air. The CO2 sorption/desorption ability of the annealed powder has been investigated by thermogravimetric analysis and Fourier transform infrared spectroscopy. When Li2ZrO3 nanopowder was exposed to CO2 environment at 500 ?C, the theoretical absorption weight was gained within 250 min with high sorption rate. Absorbed CO2 was mostly generated by heating at 800 st.C.
7
Content available remote Transparent (1-x)TiO2-xFe2O3 (x = O,5,10,15 and 20 mol%) thin films prepared by sol-gel process
Hwang K. S., Jeon Y. S., Jeon K. O., Kim B. H.
Optica Applicata
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2005
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Vol. 35, nr 2
191-199
EN
Transparent iron-doped titanium oxide thin films were prepared on soda-lime-silica glass substrate from a titanium naphthenate precursor. Films prefired at 500°C for 10 min were finally annealed at 500°C for 30 min in air. Field emission-scanning electron microscope and scanning probe microscope were used for characterizing the surface structure of the film. A sharp absorption edge of the film was observed. The film containing iron showed a shift towards the visible in the absorption threshold.
8
Content available remote Chemical durability of ß-wollastonite-reinforced glass-ceramics prepared from waste fluorescent glass and calcium carbonate
Kim B. H., Kang B. A., Yun Y. H., Hwang K. S.
Materials Science Poland
|
2004
|
Vol. 22, No. 2
83--91
EN
We prepared glass-ceramics reinforced by ß-wollastonite using waste fluorescent glass to resolve the environmental problem. Fluorescent glass and calcium carbonate were used as starting materials. The chemical durability of specimens heat-treated at 800 °C, 900 °C, and 1000 °C was analyzed by both measuring weight change and observing surface morphology. Specimen composition was determined with energy dispersive X-ray spectroscopy. As the heat treatment temperature was increased from 800 °C to 1000 °C, the chemical durability decreased, especially in the glass-matrix area. A compressive strength of about 250-350 MPa was sufficiently large for practical use.
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