• 한국표면공학회지
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• 제54권6호
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• pp.348-356
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• 2021

In this study, optical diagnosis of plasma was performed for nitrogen doping in graphene using a horizontal inductively coupled plasma (ICP) system. Graphene was prepared by mechanical exfoliation and the ICP system using nitrogen gas was ignited for plasma-induced and defect-suppressed nitrogen doping. In order to derive the optimum condition for the doping, plasma power, working pressure, and treatment time were changed. Optical emission spectroscopy (OES) was used as plasma diagnosis method. The Boltzmann plot method was adopted to estimate the electron excitation temperature using obtained OES spectra. Ar ion peaks were interpreted as a reference peak. As a result, the change in the concentration of nitrogen active species and electron excitation temperature depending on process parameters were confirmed. Doping characteristics of graphene were quantitatively evaluated by comparison of intensity ratio of graphite (G)-band to 2-D band, peak position, and shape of G-band in Raman profiles. X-ray photoelectron spectroscopy also revealed the nitrogen doping in graphene.

• Current Photovoltaic Research
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• 제4권1호
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• pp.25-29
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• 2016

$Eu^{3+}$-activated $MgMoO_4$ phosphor thin films were grown at $400^{\circ}C$ on quartz substrates by radio-frequency magnetron sputter deposition from a 15 mol% Eu-doped $MgMoO_4$ target. After the deposition, the phosphor thin films were annealed at several temperatures for 30 min in air. The influence of thermal annealing temperature on the structural and optical properties of $MgMoO_4:Eu^{3+}$ phosphor thin films was investigated by using X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible spectrophotometry. The transmittance, optical band gap, and intensities of the luminescence and excitation spectra of the thin films were found to depend on the thermal annealing temperature. The XRD patterns indicated that all the thin films had a monoclinic structure with a main (220) diffraction peak. The highest average transmittance of 91.3% in the wavelength range of 320~1100 nm was obtained for the phosphor thin film annealed at $800^{\circ}C$. At this annealing temperature the optical band gap energy was estimated as 4.83 eV. The emission and excitation spectra exhibited that the $MgMoO_4:Eu^{3+}$ phosphor thin films could be effectively excited by near ultraviolet (281 nm) light, and emitted the dominant 614 nm red light. The results show that increasing RTA temperature can enhance $Eu^{3+}$ emission and excitation intensity.

• 한국재료학회지
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• 제27권6호
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• pp.339-344
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• 2017

A series of $CaNb_2O_6:Dy^{3+}$, $CaNb_2O_6$:$Eu^{3+}$ and $CaNb_2O_6:Dy^{3+}$, $Eu^{3+}$ phosphors were prepared by solid-state reaction process. The effects of activator ions on the structural, morphological and optical properties of the phosphor particles were investigated. XRD patterns showed that all the phosphors had an orthorhombic system with a main (131) diffraction peak. For the $Dy^{3+}$-doped $CaNb_2O_6$ phosphor powders, the excitation spectra consisted of one broad band centered at 267 nm in the range of 210-310 nm and three weak peaks; the main emission band showed an intense yellow band at 575 nm that corresponded to the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transition of $Dy^{3+}$ ions. For the $Eu^{3+}$-doped $CaNb_2O_6$ phosphor, the emission spectra under ultraviolet excitation at 263 nm exhibited one strong reddish-orange band centered at 612 nm and four weak bands at 536, 593, 650, and 705 nm. For the $Dy^{3+}$ and $Eu^{3+}$-codoped $CaNb_2O_6$ phosphor powders, blue and yellow emission bands due to the $^4F_{9/2}{\rightarrow}^6H_{15/2}$ and $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transitions of $Dy^{3+}$ ions and a main reddish-orange emission line at 612 nm resulting from the $^5D_0{\rightarrow}^7F_2$ transition of $Eu^{3+}$ ions were observed. As the concentration of $Eu^{3+}$ ions increased from 1 mol% to 10 mol%, the intensities of the emissions due to $Dy^{3+}$ ions rapidly decreased, while those of the emission bands originating from the $Eu^{3+}$ ions gradually increased, reached maxima at 10 mol%, and then slightly decreased at 15 mol% of $Eu^{3+}$. These results indicate that white light emission can be achieved by modulating the concentrations of the $Eu^{3+}$ ions incorporated into the $Dy^{3+}$-doped $CaNb_2O_6$ host lattice.

• 한국물환경학회지
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• 제37권5호
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• pp.344-354
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• 2021

Optical methods such as UV and fluorescence spectrophotometers can be applied not only in the qualitative analysis of dissolved organic matter (DOM), but also in real-time quantitative DOM monitoring for wastewater and natural water. In this study, we measure the UV₂₅₄ and fluorescence excitation emission spectra for a sewage treatment plant influent and effluent, and river water before and after sewage effluent flows into the river to examine the composition and origin of DOM. In addition, a correlation analysis between quantified DOM characteristics and dissolved organic carbon (DOC) was conducted. Based on the fluorescence excitation emission spectra analysis, it was confirmed that the protein-type tryptophan-like DOM was the dominant substance in the influent, and that the organic matter exhibited relatively more humic properties after biological treatment. However, DOM in river water showed the fluorescence characteristics of terrestrial humic-like and algal tyrosine-like (protein-like) organic matter. In addition, a correlation analysis was conducted between the DOC and optical indices such as UV₂₅₄, the fluorescence intensity of protein-like and humic-like organic matter, then DOC prediction models were suggested for wastewater and river monitoring during non-rainfall and rainfall events. This study provides basic information that can improve the understanding of the contribution of DOC concentration by DOM components, and can be used for organic carbon concentration management in wastewater and natural water.

• 한국재료학회지
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• 제18권11호
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• pp.623-627
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• 2008

For possible applications as luminescent materials for white-light emission using UV-LEDs, $Ba_2Mg(PO_4)_2:Eu^{2+}$ phosphors were prepared by a solid state reaction. The photoluminescence properties of the phosphor were investigated under ultraviolet ray (UV) excitation. The prepared phosphor powders were characterized to from a single phase of a monoclinic crystalline structure by a powder X-ray diffraction analysis. In the photoluminescence spectra, the $Ba_2Mg(PO_4)_2:Eu^{2+}$ phosphor showed an intense emission band centered at the 584 nm wavelength due to the f-d transition of the $Eu^{2+}$ activator. The optimum concentration of $Eu^{2+}$ activator in the $Ba_2Mg(PO_4)_2$ host, indicating the maximum emission intensity under the excitation of a 395 nm wavelength, was 5 at%. In addition, it was confirmed that the $Eu^{2+}$ ions are substituted at both $Ba^{2+}$ sites in the $Ba_2Mg(PO_4)_2$ crystal. On the other hand, the critical distance of energy transfer between $Eu^{2+}$ ions in the $Ba_2Mg(PO_4)_2$ host was evaluated to be approximately 19.3 A. With increasing temperature, the emission intensity of the $Ba_2Mg(PO_4)_2$:Eu phosphor was considerably decreased and the central wavelength of the emission peak was shifted toward a short wavelength.

• 한국표면공학회지
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• 제50권4호
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• pp.282-288
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• 2017

$Eu^{3+}$- or $Sm^{3+}$-doped $La_2MoO_6$ phosphors were synthesized with different concentrations of activator ions via a solid-state reaction. The X-ray diffraction patterns exhibited that crystalline structures of all the phosphors were tetragonal systems with the dominant peak occurring at (103) plane, irrespective of the concentration and the type of activator ions. The crystallites showed the pebble-like crystalline shapes and the average crystallite size increased with a tendency to agglomerate as the concentration of $Eu^{3+}$ ions increased. The excitation spectra of $Eu^{3+}$-doped $La_2MoO_6$ phosphors contained an intense charge transfer band centered at 331 nm in the range of 250-370 nm and three weak peaks at 381, 394, and 415 nm, respectively, due to the $^7F_0{\rightarrow}^5L_7$, $^7F_0{\rightarrow}^5L_6$, and $^7F_0{\rightarrow}^5D_3$ transitions of $Eu^{3+}$ ions. The emission spectra under excitation at 331 nm exhibited a strong red band centered at 620 nm and two weak bands at 593 and 704 nm. As the concentration of $Eu^{3+}$ increased from 1 to 20 mol%, the intensities of all the emission bands gradually increased. For the $Sm^{3+}$-doped $La_2MoO_6$ phosphors, the emission spectra consisted of an intense emission band at 607 nm arising from the $^4G_{5/2}{\rightarrow}^6H_{7/2}$ transition and three relatively small bands at 565, 648, and 707 nm originating from the $^4G_{5/2}{\rightarrow}^6H_{5/2}$, $^4G_{5/2}{\rightarrow}^6H_{9/2}$, and $^4G_{5/2}{\rightarrow}^6H_{11/2}$ transitions of $Sm^{3+}$, respectively. The intensities of all the emission bands approached maxima when concentration of $Sm^{3+}$ ions was 5 mol%. These results indicate that the optimum concentrations for highly-luminescent red and orange emission are 20 mol% of $Eu^{3+}$ and 5 mol% of $Sm^{3+}$ ions, respectively.

• Current Optics and Photonics
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• 제3권2호
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• pp.135-142
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• 2019

We report the precipitation of ZnO nanocrystals, Ag-clusters, and Ag nanoparticles in Ag/Er/Yb doped borate glasses by furnace annealing and $CO_2$ laser annealing. The XRD analysis revealed the precipitation of ZnO and Ag phases. The absorption spectra, the TEM and energy dispersive spectroscopy (EDS) revealed the incorporation of Er and Yb ions into ZnO nanocrystals formed by a laser technique and showed the surface plasmon band of Ag nanoparticles. The down-converted blue emission intensity of $Er^{3+}$ ions obtained under 365 nm excitation was enhanced by more than a hundred times in the glass treated by furnace annealing, mainly due to the energy transfer from Ag-clusters. Moreover, we discussed the contribution of Ag nanoparticles and defects to emission characteristics in the glasses treated by two annealing techniques. Up-conversion emissions of the $Er^{3+}$ ions under 980 nm excitation were enhanced due to the incorporation of $Er^{3+}$ and $Yb^{3+}$ ions into ZnO nanocrystals after thermal treatments.

• 한국세라믹학회지
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• 제54권5호
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• pp.422-428
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• 2017

Single-phase yellow phosphor, $CaGd_{2-x}ZrSc(AlO_4)_3:xCe^{3+}$ ($CGZSA:Ce^{3+}$), possessing cubic symmetry with varied $Ce^{3+}$ concentrations, was synthesized using the solid-state reaction method. The samples were characterized using X-ray diffraction (XRD), excitation spectra, emission spectra, thermal quenching, and decay curves. The cubic phase of $CGZSA:Ce^{3+}$ phosphor was confirmed via XRD analysis. The photoluminescence spectra of $CGZSA:Ce^{3+}$ phosphor demonstrated that the phosphor could be excited at the wavelength of 440 nm; a broad yellow emission band was centered at 541 nm. These results indicate that the phosphors are adequately excited by blue light and have the potential to function as yellow-emitting phosphors for applications in white light-emitting diodes.

• 한국표면공학회지
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• 제54권3호
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• pp.112-118
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• 2021

Dy³⁺- and Eu³⁺-codoped BaWO₄ phosphors for white light-emitting diode were synthesized with different activator ions via a solid-state reaction process. The structural, morphological, and optical properties of the BaWO₄:Dy³⁺,Eu³⁺ phosphors were investigated as a function of Eu³⁺ concentration at a fixed concentration of Dy³⁺ ions. XRD patterns exhibited that all the synthesized phosphors had a tetragonal system, irrespective of the concentrations of Dy³⁺ and Eu³⁺ ions. The excitation spectra of the synthesized phosphors were composed of three intense bands centered at 251, 355, and 393 nm and several weak peaks. For the BaWO₄:Dy³⁺,Eu³⁺ phosphors synthesized with 1 mol% of Eu³⁺, the emission spectra under ultraviolet excitation at 393 nm showed two strong blue and yellow bands at 485 and 577 nm corresponding to the ⁴F_9/2⁶H_15/2 and ⁴F_9/2⁶H_13/2 transitions of Dy³⁺ ions, respectively and several weak bands in the range of 600-700 nm resulting from the 4f transitions of Eu³⁺ ions. As the concentration of Eu³⁺ ions increased, intensities of the blue and yellow emission bands gradually decreased while those of the red emissions increased rapidly and the energy transfer efficiency from Dy³⁺ to Eu³⁺ ions was 95.3% at 20 mol% of Eu³⁺. The optimum white light emission with x=0.363, y=0.357 CIE 1931 chromaticity coordinates was obtained for the sample doped with 5 mol% Dy³⁺ and 1 mol% of Eu³⁺.

• 한국표면공학회지
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• 제54권2호
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• pp.96-101
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• 2021

NaNbO₃:Eu³⁺ phosphor thin films were grown on quartz substrates by radio-frequency magnetron sputtering at a growth temperature of 100 ℃, with subsequent annealing at temperatures of 800, 900, and 1000 ℃. The effects of annealing temperature on the structural, morphological, and optical properties of the thin films were investigated. The NaNbO₃:Eu³⁺ sputtering target was synthesized by a solid-state reaction of raw materials Na₂CO₃, Nb₂O₅, and Eu₂O₃. The X-ray diffraction patterns exhibited that the thin films had two mixed phases of NaNbO₃ and Eu₂O₃. Surface morphologies were investigated by using field emission-scanning electron microscopy and indicated that the grains of the thin film annealed at 1000 ℃ showed irregular shapes with an average size of approximately 300 nm. The excitation spectra of Eu³⁺-doped NaNbO₃ thin film consisted of a strong charge transfer band centered at 304 nm in the range of 240-350 nm and two weak peaks at 395 and 462 nm, respectively, resulting from the ⁷F₀→⁵L₆ and ⁷F₀→⁵H₂ transitions of Eu³⁺ ions. The emission spectra under excitation at 304 nm exhibited an intense red band centered at 614 nm and two weak bands at 592 and 681 nm. As the annealing temperature increased from 800 ℃ to 1000 ℃, the intensities of all the emission bands and the band gap energies gradually increased. These results indicate that the higher annealing temperature enhance the luminescent properties of NaNbO₃:Eu³⁺ thin films.