• Korean Journal of Materials Research
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• v.16 no.6
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• pp.394-399
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• 2006

Ferroelectric $HoMnO_3$ thin films were deposited on the Si(100) substrate at $700^{\circ}C$ for 2 hrs by metalorganic chemical vapor deposition (MOCVD) and post-annealed at 850oC by rapid thermal process (RTP). Electrical properties and crystalline phases of $HoMnO_3$ thin films were investigated as a function of postannealing time. Single phase of hexagonal symmetry with c-axis preferred orientation was obtained from $HoMnO_3$ thin films post-annealed at $850^{\circ}C$ for 5 min, while the c-axis preferred orientation was decreased with the increase of post-annealing time, and the thin films post-annealed at $850^{\circ}C$ for 15 min showed the mixture phases of hexagonal and orthorhombic symmetry. P-E (Polarization-Electric field) hysteresis loop of ferroelectric $HoMnO_3$ thin films was observed only for the single phase of hexagonal symmetry, but that was not observed for the mixture phases of the hexagonal and orthorhombic symmetry, which was discussed with the bond valence of Mn ion of crystalline phase. Leakage current density was dependent on the microstructure of thin films as well as the change of valence of Mn ion.

• Journal of the Korean Ceramic Society
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• v.52 no.1
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• pp.66-71
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• 2015

$NaY_{1-x}(WO_4)_2:Ho^{3+}/Yb^{3+}$ phosphors with doping concentrations of $Ho^{3+}$ and $Yb^{3+}$ ($x=Ho^{3+}+Yb^{3+}$, $Ho^{3+}=0.05$, 0.1, 0.2, and $Yb^{3+}=0.2$, 0.45) were successfully synthesized via the cyclic microwave-modified sol-gel route; their upconversion properties were investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of $2-5{\mu}m$. Under excitation at 980 nm, the synthesized particles exhibited yellow emissions based on a strong 550-nm emission band in the green region and a very strong 655-nm emission band in the red region. The Raman spectra of the doped particles indicated the domination of strong peaks at higher and lower frequencies induced by the incorporation of the $Ho^{3+}$ and $Yb^{3+}$ elements into the $Y^{3+}$ sites in the crystal lattice, which resulted in unit cell shrinkage that accompanied a new phase formation of the $WO_{4-x}$ group.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.757-763
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• 2016

$Ho^{3+}/Yb^{3+}/Tm^{3+}$ tri-doped $NaY_{1-x}(WO_4)_2$ phosphors with proper doping concentrations of $Ho^{3+}$, $Yb^{3+}$ and $Tm^{3+}$ ($x=Ho^{3+}+Yb^{3+}+Tm^{3+}$, $Ho^{3+}$=0.04, 0.03, 0.02, 0.01, $Yb^{3+}$=0.35, 0.40, 0.45, 0.50 and $Tm^{3+}$=0.01, 0.02, 0.03, 0.04) were successfully synthesized via the microwave sol-gel route, and their upconversion properties were investigated. Well-crystallized microcrystalline particles showed fine and homogeneous microcrystalline morphology with particle sizes of $1-2{\mu}m$. The optical properties were comparatively examined using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the doped particles exhibited white emissions based on blue, green and red emission bands, which correspond to the $^1G_4{\rightarrow}^3H_6$ transitions of $Tm^{3+}$ in the blue region, the $^5S_2/^5F_4{\rightarrow}^5I_8$ transitions of $Ho^{3+}$ in the green region, the $^5F_5{\rightarrow}^5I_8$ transitions of $Ho^{3+}$, and the $^1G_4{\rightarrow}^3F_4$ and $^3H_4{\rightarrow}^3H_6$ transitions of $Tm^{3+}$ in the red region. The pump power dependence of the upconversion emission intensity and the Commission Internationale de L'Eclairage chromaticity coordinates of the phosphors were evaluated in detail.

• The Korean Journal of Nuclear Medicine
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• v.30 no.3
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• pp.351-360
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• 1996

Chitosan is a polysaccharide of natural orgin obtained by full or partial deacetylation of chitin, a very abudant natural polymer, which has the properties of biocompatibilities, bioaffinities, and biodegradabilities. The free amino group of chitosan should be participated in forming chelate with holmium (${\beta}$-emitter). $^{166}Ho(NO_3)_3\;5H_2O$ of high radionuclidic purity of upto 99.9% was made by neutron irradiation of naturally occuring $^{166}Ho(NO_3)_3\;5H_2O$, and then reacted with the prepared chitosan solution. The effect of pH, reaction time, the concentration and viscosity of chitosan and the amount of $^{166}Ho$ on forming $^{166}Ho$-chitosan complex ($^{166}Ho$-CHICO) were investigated. $^{166}Ho$-chitosan macroaggregate($^{166}Ho$-CHIMA) was made from $^{166}Ho$-CHICO. Their physical properties such as radionuclidic purity, particle size distribution, stability in vitro and vivo were examined. Their high in vitro and vivo stability makes them attractive agents for internal radiotherapy by local administeration.

• Journal of the Korean Ceramic Society
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• v.53 no.4
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• pp.456-462
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• 2016

$NaCaGd(MoO_4)_3:Ho^{3+}/Yb^{3+}$ ternary molybdates were successfully synthesized by microwave sol-gel method for the first time. Well-crystallized particles formed after heat-treatment at $900^{\circ}C$ for 16 h showed a fine and homogeneous morphology with particle sizes of $3-5{\mu}m$. Under excitation at 980 nm, the UC intensities of the doped samples exhibited strong yellow emissions based on the combination of strong emission bands at the 520-nm and 630-nm emission bands in the green and red spectral regions, respectively. The strong 520-nm emission band in the green region corresponds to the $^5S_2/^5F_4{\rightarrow}^5I_8$ transition of $Ho^{3+}$ ions, while the strong 630-nm emission band in the red region appears to be due to the $^5F_5{\rightarrow}^5I_8$ transition of the $Ho^{3+}$ ions. The optimal $Yb^{3+}:Ho^{3+}$ ratio was found at 9:1, as indicated by the composition-dependent quenching effect of $Ho^{3+}$ ions. The pump power dependence of the upconversion emission intensity and the Commission Internationale de L'Eclairage chromaticity coordinates of the phosphors were evaluated in detail.

• Bulletin of the Korean Chemical Society
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• v.19 no.2
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• pp.231-235
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• 1998

Two holmium β-diketonate complexes, Ho(hfa)3(H2O)2 (1) and [Ho(hfa)3(H2O)2](triglyme) (2), have been prepared and characterized by IR, TGA, and single-crystal X-ray analyses. These complexes show polymeric chains by the intermolecular hydrogen bondings. The donor atoms of the intermolecular hydrogen bonding in both complexes are hydrogen atoms of the coordinated water molecules. The acceptor atoms in 1 are the carbonyl oxygen atoms of β-diketonate ligands whereas those in 2 are oxygen atoms of the triglyme ligand. While compound 1 decomposes cleanly to Ho2O3, compound 2 sublimes intact. Crystal data for 1 and 2 are as follows: Ho(hfa)3(H2O)2 triclinic P1, a=10.158(4), b=11.628(2), c=12.579(6) Å, α=67.02(3)°, β=73.95(4)°, γ=76.12(2)°, V=1299.8(8) Å3. [Ho(hfa)3(H2O)2](triglyme), monoclinic P21/c, a=12.559(3), b=19.111(2), c=16.789(6) Å, β=110.59(4)°, V=3772(2) Å3.

• Korean Chemical Engineering Research
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• v.53 no.5
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• pp.620-626
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• 2015

$Ho^{3+}$ doped $SrAl_2O_4$ upconversion phosphor powders were synthesized by spray pyrolysis, and the crystallographic properties and luminescence characteristics were examined by varying activator concentrations and heattreatment temperatures. The effect of organic additives on the crystal structure and luminescent properties was also investigated. $SrAl_2O_4:Ho^{3+}$ powders showed intensive green emission due to the $^5F_4/^5S_2{\rightarrow}^5I_8$ transition of $Ho^{3+}$. The optimal $Ho^{3+}$ concentration in order to achieve the highest luminescence was 0.1%. Over this concentration, emission intensities were largely diminished via a concentration quenching due to dipole-dipole interaction between activator ions. According to the dependence of emission intensity on the pumping power of a laser diode, it was clear that the upconversion of $SrAl_2O_4:Ho^{3+}$ occurred via the ground state absorption-excited state absorption processes involving two near-IR photons. Synthesized powders were monoclinic as a major phase, having some hexagonal phase. The increase of heat-treatment temperatures from $1000^{\circ}C$ to $1350^{\circ}C$ led to crystallinity enhancement of monoclinic phase, reducing hexagonal phase. The hexagonal phase, however, did not disappear even at $1350^{\circ}C$. When both citric acid (CA) and ethylene glycol (EG) were added to the spray solution, the resulting powders had pure monoclinic phase without forming hexagonal phase, and led to largely enhancement of crystallinity. Also, N,N-Dimethylformamide (DMF) addition to the spray solution containing both CA and EG made it possible to effectively reduce the surface area of $SrAl_2O_4:Ho^{3+}$ powders. Consequently, the $SrAl_2O_4:Ho^{3+}$ powders prepared by using the spray solution containing CA/EG/DMF mixture as the organic additives showed about 168% improved luminescence compared to the phosphor prepared without organic additives. It was concluded that both the increased crystallinity of high-purity monoclinic phase and the decrease of surface area were attributed to the large enhancement of upconversion luminescence.

• Korean Journal of Materials Research
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• v.29 no.12
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• pp.741-746
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• 2019

New triple tungstate phosphors NaPbLa(WO₄)₃:Yb³⁺/Ho³⁺ (x = Yb³⁺/Ho³⁺ = 7, 8, 9, 10) are successfully fabricated by microwave assisted sol-gel synthesis and their structural and frequency upconversion (UC) characteristics are investigated. The compounds crystallized in the tetragonal space group I4₁/a and the NaPbLa(WO₄)₃ host have unit cell parameters a = 5.3927(1) and c = 11.7961(3) Å, V = 343.05(2) ų, Z = 4. Under excitation at 980 nm, the phosphors have yellowish green emissions, which are derived from the intense ⁵S₂/⁵F₄→⁵I₈ transitions of Ho³⁺ ions in the green spectral range and strong ⁵F₅→⁵I₈ transitions in the red spectral range. The optimal Yb³⁺:Ho³⁺ ratio is revealed to be x = 9, which is attributed to the quenching effect of Ho³⁺ ions, as indicated by the composition dependence. The UC characteristics are evaluated in detail under consideration of the pump power dependence and Commission Internationale de L'Eclairage chromaticity. The spectroscopic features of Raman spectra are discussed in terms of the superposition of Ho³⁺ luminescence and vibrational lines. The possibility of controlling the spectral distribution of UC luminescence by the chemical content of tungstate hosts is demonstrated.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.6
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• pp.779-790
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• 2006

This study examines relative contributions of volatile organic compounds (VOCs) to the formation of hydroxyl (OH) and peroxy radicals such as $HO_2$ and $RO_2$ during the intensive sampling period (Jun. $1{\sim}30$, 2004) in the air of Seoul metropolitan area. As to the contribution of VOCs to $HO_x$ levels, the impact of individual VOC concentration change on $HO_2$ concentration change was more than an order of magnitude higher than that on OH concentration change during the study period. The contribution of change in isoprene concentration to $HO_2$ concentration change was 38 times higher than OH and that in the concentration of alkene compounds to $HO_2$ concentration change was 31 times higher than OH. Moreover, the concentration changes of isoprene and aromatic compounds (AROM) played significant roles in $HO_x$ concentration changes. On the other hands, aldehydes (ALD2) and alkanes (ALKA) showed anti-correlation (negative) in $HO_x$ concentration changes with low contribution ($-4{\times}10^{-3}$ pptv/ppbv (OH) and $-58{\times}10^{-3}$ ($HO_2$) for ALD2; $-1{\times}10^{-3}$ (OH) and $-15{\times}10^{-3}$ ($HO_2$) for ALKA). Unlike other VOCs, $C_2H_6$ and $C_3H_8$ showed positive or negative contribution to peroxy radicals, depending on ambient air conditions. The contribution of VOC concentration changes to changes in $CH_3O_2$ and $RO_2$ concentration showed similar pattern to $HO_x$ contribution.

• Journal of The Korean Society of Grassland and Forage Science
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• v.35 no.1
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• pp.31-35
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• 2015

This experiment was carried out to breed a very early-maturing variety of Italian ryegrass (Lolium multiflorum Lam.) in the Grassland and Forage Crops Division, National Institute of Animal Science, RDA, Cheonan, Korea from 2012 to 2014. New variety "Greenfarm3ho" is a diploid variety with a green leaf color, a semi-erect growth habit in late autumn/fall, and an erect growth habit in early spring. With a heading date of April 27, Greenfarm3ho was categorized as an early-maturing variety. Compared with the "Greenfarm" control variety, Greenfarm3ho's flag-leaf width was narrower by 0.5 mm, its flag-leaf length was longer by 4.4 cm, and its plant length was longer by 3 cm; additionally, Greenfarm3ho's stem thickness was 0.1 mm thicker and it showed winter hardiness. The dry matter (DM) yield (8,976 kg/ha) of Greenfarm3ho was similar to that of Greenfarm. The in vitro dry matter digestibility (IVDMD), total digestible nutrient (TDN), and crude protein (CP) of Greenfarm3ho were 70.0%, 64.1%, and 1.0%, respectively, which are higher than those of Greenfarm by 2.9%, 2.0%, and 1.4%, respectively. The acid detergent fiber (ADF) and neutral detergent fiber (NDF) content of Greenfarm3ho were 31.4% and 53.3%, respectively, which are lower than those of Greenfarm by 2.5% and 3.0%, respectively.