Byung Kee Moon

Pukyong National University, Busan, Busan, South Korea

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Publications (201)437.43 Total impact

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    ABSTRACT: A new and simple method for the synthesis of rare earth ion doped CaF2 (CaF2:RE3+) submicroparticles is presented, using an ionic liquids based hydrothermal process. The structural properties of the CaF2 nanoparticles were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The CaF2 nanoparticles exhibited a sphere-like morphology with a diameter of about 150 nm. During the synthesis, the ionic liquid [bmim]BF4 (1-butyl, 2-methylimidazolium tetrafluoroborate) acts as both a co-solvent and reactant. The crucial effect of EDTA-2Na (ethylene diamine tetra acetic acid disodium salt) on the formation of CaF2:RE sub-microparticles was explored and discussed. The strong green (513–569 nm) and strong red (636–685 nm) upconversion emissions of the CaF2:Er3+,Yb3+ nanoparticles (λex = 980 nm) were also investigated. The luminescent properties of CaF2:Eu3+ and CaF2:Ce3+,Tb3+ were also evaluated. This work may represent a new step in synthesizing fluoride sub-nanocrystals using ionic liquids.
    No preview · Article · Jan 2016 · Journal of Nanoscience and Nanotechnology

  • No preview · Article · Jan 2016 · Journal- Korean Physical Society
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    ABSTRACT: A series of Sm3+ doped Sr2CaMo1-xWxO6 phosphors were synthesized through solid state reaction process and their luminescent properties have been investigated. They presented excitation bands in UV, near UV and blue regions, originating from charge transfer transitions within Mo(W)O6 or Sm3+ f–f transitions. Concentration quenching still occurs among MoO6 groups even when Mo concentration is very low, however, if there is no Mo content in Sr2CaMo1-xWxO6 phosphors, absorption in near UV region cannot happen. It was found there is a big difference between the calculated optical band gap of Sr2CaMo0.02W0.98O6: 2% Sm3+ and that of Sr2CaMo0.01W0.99O6: 2% Sm3+. Band structure and density of state of Sr2CaMo0.5W0.5O6 were examined to explore the origination of charge transfer transition. Site occupation of Sm3+ in host lattice was discussed based on Raman spectra and group theory analysis. There are two kinds of luminescence centers in Sm3+ doped Sr2CaMo1-xWxO6 (x > 0) phosphors. When 98% Mo were substituted by W, the excitation band at 350 nm by monitoring 608 nm emission in Sr2CaMo0.02W0.98O6: 2%Sm3+ is about 8.5 times stronger than that in Sr2CaMoO6: 2%Sm3+. Energy transfer process was also discussed considering the overlap between the emission spectrum of Mo(W)O6 groups and the absorption spectrum of Sm3+, as well as the atom arrays of Mo6+(W6+), O2− and Sm3+.
    No preview · Article · Dec 2015 · Journal of Alloys and Compounds
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    ABSTRACT: Abstract A narrow high intensity red-emitting double-perovskite type phosphor SrLa1-xMgTaO6:xEu3+ was successfully synthesized by a solid-state reaction method. Under the excitation of the near UV and blue light, this phosphor exhibited intense red emission that can improve the color qualities of warm light-emitting diodes. Due to the Eu3+ ions being an intrinsically asymmetric cation environment, the dominant emission peak emitted from the transition 5D0→7F2 is extraordinarily stronger than that of 5D0→7F1, the ratio I0-2/I0-1 was about 8.67. And owing to the most Eu3+ ions locating at same crystal field environment, a full-width at half-maximum (FWHM) of this peak was very narrow (6.49 nm) at room temperature. Energy transfer between Eu3+ ions were demonstrated from dipole-dipole interaction, and the critical distance was estimated to be 9.31 Å. When Eu3+ ions' concentration reaches 30%, the emission intensity was observed about three times higher than that of a commercial red phosphor Y2O3:Eu3+, and the Commission International de L'Eclairage chromaticity coordinates was calculated at (0.66, 0.33). All the results confirmed that SrLa(1-x)MgTaO6:xEu3+ phosphors might be promising for use in white LEDs.
    Preview · Article · Oct 2015 · Journal of Luminescence
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    ABSTRACT: A novel Sm3+-doped Sr2CaWO6 (SCWO) red phosphor, synthesized though a solid-state reaction, was reported. Its crystal structure was analyzed and refined via the Rietveld full-pattern fitting method based on XRD patterns. The CASTEP module of Materials Studio was used to investigate the band structure and density of states of the SCWO. The optical band gap was calculated through the UV-vis diffuse reflectance spectrum and compared with the value predicted by the DFT method. Raman spectra were recorded to confirm the substitution of cations by Sm3+ ions. The broad W-O charge transfer band and narrow excitation band at 406 nm from Sm3+ ions have comparable intensities in SCWO:Sm3+. After the introduction of charge compensators Li+, Na+ or K+, the intensity of the near-UV excitation band at 406 nm was almost twice as much as before. The profiles of the emission spectra under excitation into the charge transfer absorption and f-f transition of Sm3+ are different, and low-symmetry Sm3+ centres are preferentially excited via f-f absorption transitions. The intensity ratios of electronic, magnetic dipole-allowed transitions under different radiations show that the charge compensators can influence the chemical environment around Sm3+.
    No preview · Article · Oct 2015 · RSC Advances
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    ABSTRACT: Monoclinic-structured BiVO4 microcrystals with butterfly-like morphology were synthesized with alcoho-hydrothermal method. Compared with irregular morphologies BiVO4, the butterfly-like BiVO4 possessed higher surface area and lower energy band gap, which is conducive to promote the rapid adsorption of organic pollutants on the surface of BiVO4 and absorb the light with lower energy. Photocatalysis experiment results showed that the degradation efficiency of the butterfly-like BiVO4 for degradation MO solution is far higher than irregular morphologies BiVO4. It indicates the excellent photocatalytic activity of the butterfly-like BiVO4 may be related to its special morphology, high surface area, and low band gap energy.
    No preview · Article · Oct 2015 · Synthesis and Reactivity in Inorganic Metal-Organic and Nano-Metal Chemistry
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    ABSTRACT: The experimental and theoretical studies of the optical properties of SrMoO4:Tb3+ phosphors were carried out. The structural, optical, and electronical properties of the phosphors were systematically studied. The phosphor samples were crystallized at different temperatures via a sol-gel method. Excitation spectra of SrMoO4:Tb3+ powder samples exhibited gradual red shift and luminescent intensity changed with increasing the sintering temperature. Such spectral changes depend strongly on the crystallographic properties such as lattice parameters and crystallinity. The shift of the excitation spectra is mainly ascribed to the covalent bond interaction between Mo-O bonds. An energy band model was demonstrated to describe the luminescence mechanism in the material.
    Full-text · Article · Oct 2015 · Materials Research Bulletin
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    ABSTRACT: A series of 6 mol% Eu3+ doped Gd2MoO6 samples were prepared by using the sol–gel method. The X-ray diffraction patterns of the samples confirmed their monoclinic structure after they were annealed at 1300 °C, and a scanning electron microscope image revealed closely packed particles. The excitation spectra showed that the intensity of the excitation band decreased and the charge transfer band shifted from 370 to 350 nm with decreasing sintering temperature. The emission spectra are dominated by the hypersensitive forced electron dipolar transition 5D 0 → 7F 2 at 612 nm. The as synthesized phosphor can be used as a red phosphor in white light emitting diodes.
    No preview · Article · Oct 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: Eu3+ doped CaGd4O7 phosphors have been newly synthesized using a solvothermal reaction method and sintered at 1400 °C. The phase, composition, morphologies, and photoluminescent properties of the phosphors have been well characterized by means of the X-ray diffraction (XRD) patterns, energy dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL) spectroscopy, and decay curves, respectively. The XRD patterns of the as-prepared phosphors confirm their monoclinic structure and the FE-SEM images reveal flower-like morphology, formed through agglomeration. The calculated size of the crystallites was approximately 83 nm. The photoluminescence excitation (PLE) spectra of CaGd4O7: Eu3+ phosphors consist of a broad band due to the charge transfer (CT) electronic transition, and several sharp peaks that can be attributed to the f–f transitions of Eu3+ and Gd3+. The PL spectra exhibited a stronger red emission corresponding to the 5D0→7F2 transition. The CIE chromaticity coordinates of the phosphors were calculated and all the chromaticity coordinates have been placed in the red spectral region. These luminescent powders are expected to have potential applications for white light-emitting diodes (WLEDs) and optical display systems.
    No preview · Article · Oct 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: Sub-micron sized ZrO2 spheres were synthesized by a facile solvothermal reaction method. The influence of Zr(OPr)4 concentration on the size and size distribution of ZrO2 spheres were examined by taking the scanning electron microscope and transmission electron microscope images. When the concentration of Zr(OPr)4 was increased from 0.031 to 0.045 mol, the average size of the spheres also increased from 305 to 920 nm. The diffused reflectance spectra of the calcined ZrO2 spheres exhibited the higher reflectivity than that of as-prepared ZrO2 spheres. As compared to the bare LEDs, light extraction efficiency was improved to 23% when the ZrO2 spheres were coated on the ITO surface, however, 70.12% was improved when the ZrO2 spheres were coated on the GaN surface due to the spherical morphology induced photon escape cone enhancement.
    Full-text · Article · Sep 2015 · RSC Advances
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    ABSTRACT: Er3+/Yb3+ co-doped Sr2CeO4 phosphors were synthesized using a high-energy ball milling method at 1100 °C. The X-ray diffraction patterns confirmed their orthorhombic structure. The up-conversion emissions corresponding to 2H11/2→4I15/2, S3/2→4I15/2 and 4F9/2→4I15/2 transitions peaking at 526 nm, 552 nm and 669 nm have been observed under 975 nm excitation. With the help of a schematic energy level diagram the up-conversion mechanisms were discussed in detail. The excited state absorption and energy transfer process were discussed as possible up-conversion mechanisms. The energy back transfer (4S3/2+2F7/2→4I13/2+2F5/2) contribute the increased intensity ratio of red to green emission in Sr2CeO4:Er3+/Yb3+ samples. A decay curve analysis for the UC emission corresponding to the 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions in the Er3+/Yb3+ co-doped Sr2CeO4 phosphors was performed. The CIE chromaticity coordinates of the Er3+/Yb3+ co-doped Sr2CeO4 phosphors were located in the green region. The results indicate that the material may be suitable for applications in the fields of color displays and light emitting devices.
    No preview · Article · Jul 2015 · Ceramics International
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    ABSTRACT: Well-crystallized nanorod bundles Ln4O(OH)9NO3:1%Eu(Ln = Y, Lu) have been successfully prepared by hydrothermal method. The crystalline phase, size and optical properties were characterized using powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), infrared (IR) spectrograph and photoluminescent (PL) spectra. Site occupations of Eu3+ in crystals Ln4O(OH)9NO3:Eu(Ln = Y, Lu) were discussed based on excitation spectra and the empirical relationship formula between the charge transfer (CT) energy and the environmental factor. The emission spectra exhibited that the strongest emission peaks with an excitation wavelength of 395 nm were at 617 and 626 nm in crystal Lu4O(OH)9NO3:1%Eu and Y4O(OH)9NO3:1%Eu, respectively, both of which come from 5D0–7F2 transition of the Eu3+ ions. The broad excitation peaks at about 254 and 255 nm were found when monitored at 617 and 628 nm in crystal Lu4O(OH)9NO3:1%Eu and Y4O(OH)9NO3:1%Eu, respectively, which were due to O–Eu CT transition. Based on the dielectric theory of complex crystal, the CT bands at about 254 and 255 nm in Ln4O(OH)9NO3:1%Eu(Ln= Y, Lu) were assigned to the transition of O–Eu at Ln3(Ln= Y, Lu) site, from which we can conclude that Eu3+ ions occupied the site of Ln3(Ln = Y, Lu) in crystal Ln4O(OH)9NO3:1%Eu(Ln = Y, Lu). It put forward a new route to investigate site occupation of luminescent center ions in rare earth doped complex inorganic luminescence materials.
    No preview · Article · Jul 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: CaMoO4:Eu3+ red phosphors were successfully synthesized by using a high-energy ball milling method. The X-ray diffraction patterns confirmed their tetragonal structure, and the field emission scanning electron microscopy images exhibited spherical particles. The photoluminescence properties (PL) of CaMoO4:Eu3+ phosphors were also studied as a function of the sintering temperature and the Eu3+ ion concentration. The PL excitation and the PL spectra demonstrated that CaMoO4 doped with 5 mol% of Eu3+ and sintered at 1200 °C showed an intense charge transfer band with a band maximum at around 303 nm and the strongest red emission at 618 nm (5D0 → 7F2) with Commision Internationale de I’Eclairage 1931 chromaticity coordinates (0.609, 0.343).
    No preview · Article · Jun 2015 · Journal- Korean Physical Society
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    ABSTRACT: Dual-mode excitation properties were introduced in Sm3+ doped Sr2CaMoO6 prepared by a high temperature solid state reaction technique. Two ways are available to generate white light in the single-component phosphor activated by Sm3+ ions. Warm white light can be obtained from Sr1.995Sm0.005CaMoO6 phosphor with 380 nm or 410 nm excitation energy. The full visible spectral emission of the single-phase phosphor comes from the high and low level emission lines of Sm3+ ions as well as the intrinsic luminescence of MoO6 group. It is also competitive as yellow-emitting phosphor for blue pumped white LEDs and gives three emission bands at 567, 603 and 650 nm, presenting yellow luminescence upon 466 nm radiation. The 650 nm red emission band corresponding to 4G5/2→6H9/2 transition of Sm3+ can can make its color rendering index better. The excellent photoluminescence of Sr2CaMoO6 is related to the partial tilting (Ca/Mo)O6 and octahedra and therefore lowered symmetry, which were confirmed by General Structure Analysis System. Band gap of Sr2CaMoO6 estimated from the diffuse reflection spectra and also calculated by CASTEP mode shows its semi-conducting character. All the results show that Sr2-xSmxCaMoO6 phosphors have considerable potential for use in near UV LED or pumped by blue LED chip.
    No preview · Article · Jun 2015 · The Journal of Physical Chemistry C
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    ABSTRACT: White light-emitting diode (WLED) products currently available on the market are based on the blue LED combined with yellow phosphor approach. However, these WLEDs are still insufficient for general illumination and flat panel display (FPD) applications because of their low color-rendering index (CRI < 75) and high correlated color temperature (CCT = 6000 K). Although near-ultraviolet (UV) LED chips provide more efficient excitation than blue chips, YAG:Ce3+ phosphors have very weak excitation in the near-UV spectral region. Hence, there is an increasing demand for novel yellow phosphor materials with excitation in the near-UV region. In this work, we report novel self-activated yellow Ca5Zn3.92In0.08(V0.99Ta0.01O4)6 (CZIVT) phosphors that efficiently convert near-UV excitation light into yellow luminescence. The crystal structure and lattice parameters of these CZIVT phosphors are elucidated through Rietveld refinement. Through doping with In3+ and Ta5+ ions, the emission intensity is enhanc
    Full-text · Article · May 2015 · Scientific Reports
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    ABSTRACT: It has been still a challenge to obtain a new single-component white-light phosphor with the vanadates as host lattices and with two types of ions as activators. A systematic Ln13+/Ln23+ (Ln13+/Ln23+ = Dy3+/Tm3+ or Dy3+/Sm3+ or Dy3+/Eu3+ or Tm3+/Eu3+ or Tm3+/Sm3+) coactivated Ca9Y(VO4)7 (CYV)samples as well as their singly doped CYV phosphors have been synthesized by the traditional solid state reaction and their photoluminescence properties have been investigated. The photoluminescence properties as a function of the concentration of rare earth ions have been discussed and the tunable luminescent color was found. The warm (CYV: 1%Dy3+, 1%Sm3+), natural (CYV: 7% Tm3+,0.5% Eu3+; CYV: 1.0% Tm3+, 0.5% Sm3+), and cold (CYV: 3% Tm3+,0.5% Eu3+; CYV: 0.5% Dy3+,0.5% Tm3+; CYV: 0.5% Dy3+,0.7% Tm3+; CYV: 0.3%Dy3+, 0.5% Tm3+) white lights can be obtained. Generally, the emission intensity or lifetime of one rare earth ions decreases with increasing of the concentration of another rare earth ions.
    No preview · Article · May 2015 · Materials Chemistry and Physics
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    ABSTRACT: The synthesis of pure hexagonal and monoclinic BaAl2Si2O8:Sm crystals using a simple sol-gel technique is discussed in detail. The pure hexagonal BaAl2Si2O8:Sm phase (H-BASO:Sm) can be obtained by adjusting the amount of the citric acid. The pure monoclinic BaAl2Si2O8:Sm phase (M-BASO:Sm) can be easily obtained by a three-step-calcinations process. Possibly it is the carbon existing in the crystal that can stabilize the hexagonal BaAl2Si2O8:Sm phase (H-BASO:Sm) and retard the conversion from the hexagonal to monoclinic phase. Photoluminescence, UV-vis absorption spectra and X-ray photoelectron spectra (XPS) demonstrate the existence of Sm2+ and Sm3+ ions in Sm doped H-BASO and M-BASO calcined under a reducing atmosphere. Photoluminescence properties of Sm3+ and Sm2+ ions in M-BASO and Sm2+ ions in H-BASO are reported.
    No preview · Article · Apr 2015 · Ceramics International
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    ABSTRACT: GdVO4:Yb3+, Er3+ powder was synthesized by a conventional solid state reaction. The XRD pattern confirmed that the GdVO4:Yb3+, Er3+ powder phosphors have tetragonal structure. The up-conversion photoluminescence (UCPL) spectrum consisted of 2H11/2 → 4I15/2 (525 nm) and 4S3/2 → 4I15/2 (554 nm) transition. The UCPL intensity of 2H11/2 → 4I15/2 (525 nm) is stronger than 4S3/2 → 4I15/2 (554 nm) by adjusting Yb3+ concentrations. In order to explain this behavior, we investigated a pump power dependence.
    No preview · Article · Feb 2015 · Solid State Sciences
  • Hyun Kyoung Yang · Byung Kee Moon · Jung Hyun Jeong
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    ABSTRACT: Nd:GdVO4 micro-rods were synthesized by a high energy ball milling method. The effects of sintering temperature and phase transformation of the products are investigated based on the differential thermal, and X-ray diffraction analyses. The morphological changes were observed by taking the field emission-scanning electron microscopy images, and the elemental composition was analyzed by using the energy-dispersive spectroscopy. The emission performance of the samples were investigated by luminescence spectra. Furthermore, the morphological dependent spectral properties of the synthesized samples are also discussed in detailed.
    No preview · Article · Feb 2015 · Ceramics International
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    ABSTRACT: Sr2CeO4 phosphors were prepared by means of a high-energy ball milling method and sintered at various temperatures. The X-ray diffraction patterns of the as-prepared phosphors confirmed their orthorhombic structure. The FE-SEM images revealed that the Sr2CeO4 phosphors were composed of spherical particles with diameters of less than 2 μm. The excitation spectra showed a broad band which peaks at 299 nm and has a shoulder at 349 nm due to the t1g-f and t1u-f charge transfer states of Ce4+ ions. The emission spectra exhibited a broad blue-emission band with a maximum at 478 nm that originates from the Ce4+-O2- charge transfer transition resulting from the interaction of Ce4+ ion with the neighboring oxide ions. The highest photoluminescence emission intensity was observed when the powder was sintered at 1100 °C. The results of this study indicate that Sr2CeO4 phosphors have the potential to be used in applications such as white light-emitting diodes (WLEDs) and optical display systems. © 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
    No preview · Article · Jan 2015 · Ceramics International