• Korean Journal of Materials Research
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• v.22 no.9
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• pp.489-493
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• 2012

Green phosphors $K_2BaW_2O_8:Tb^{3+}$(1.0 mol%) were synthesized by solid state reaction method. Differential thermal analysis was applied to trace the reaction processes. Three endothermic values of 95, 706, and $1055^{\circ}C$ correspond to the loss of absorbed water, the release of carbon dioxide, and the beginning of the melting point, respectively. The phase purity of the powders was examined using powder X-ray diffraction(XRD). Two strong excitation bands in the wavelength region of 200-310 nm were found to be due to the ${WO_4}^{2-}$ exciton transition and the 4f-5d transition of $Tb^{3+}$ in $K_2BaW_2O_8$. The excitation spectrum presents several lines in the range of 310-380 nm; these are assigned to the 4f-4f transitions of the $Tb^{3+}$ ion. The strong emission line at around 550 nm, due to the $^5D_4{\rightarrow}^7F_5$ transition, is observed together with weak lines of the $^5D_4{\rightarrow}^7F_J$(J = 3, 4, and 6) transitions. A broad emission band peaking at 530 nm is observed at 10 K, while it disappears at room temperature. The decay times of $Tb^{3+}$ $^5D_4{\rightarrow}^7F_5$ emission are estimated to be 4.8 and 1.4 ms, respectively, at 10 and 295 K; those of the ${WO_4}^{2-}$ exciton emissions are 22 and 0.92 ${\mu}s$ at 10 and 200 K, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.885-886
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• 2003

A bilayer is used as an anode electrode for organic electroluminescent devices. The bilayer consist of an ultrathjn ZnO layer adjacent to an hole-transporting layer and an Indium tin oxide(ITO) outerlayer. We tried to bring low the barrier between the devices as deposited ZnO films on ITO substrates. We fabricated the organic EL structure consisted of Al as cathode, $Al_{2}O_{3}$ as electro transport layer, Alq3 as luminously layer, triphenyl diamine(TPD) as hole transport layer and ZnO(l nm )/ITO(l50 nm) as anode. The result of this experiment was not good compared with the case of using ITO, Nevertheless, at this structure we obtained the lowest turn-on voltage as the value of 19 V and the good brightness (6200 $cd/m^{2}$) of the emission light from the devices. Then the quantum efficiency was to be 1.0%.

• Journal of Sensor Science and Technology
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• v.9 no.5
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• pp.341-349
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• 2000

CsI(Br) single crystals doped with 1, 3, 5 or 10 mole% $Br^-$ ions, as an activator, were grown by Czochralski method. The lattice structure of grown CsI(Br) single crystal was bcc and its lattice constant was $4.568\;{\AA}$. The absorption edge of the CsI(Br) single crystals was observed at 243 nm. The spectral range of the luminescence excited by 243 nm of wavelength was $300{\sim}600\;nm$, and its peak emission appeared at 440 nm. The luminescence intensity was maximum when CsI(Br) was doped with 3 mole % $Br^-$ ions. The energy resolutions of the CsI(Br) scintillator doped with 3 mole % $Br^-$ ions were 15.0% for $^{137}Cs$(662 keV), 13.1% for $^{54}Mn$(835 keV), and 18.0% and 6.3% for $^{22}Na$(511 keV and 1275 keV), respectively. The decay curves had fast and slow components, and the fast component was about 41 ns independent on the concentration of the $Br^-$ ions. The time resolution of CsI(Br) scintillators decreased with increasing of the concentration of $Br^-$ ions.

• Macromolecular Research
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• v.17 no.9
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• pp.672-681
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• 2009

A series of inert and photo-stable Er(III)-encapsulated complexes based on ${\pi}$-extended dendritic anthracene ligands bearing G3-aryl-ether dendron ([G3-AnX]-$CO_2H$), which retain different ${\pi}$-bridging systems, such as single (X= S), double (X= D) and triple (X= T) bonds was designed and synthesized to establish the structure-property relationship. The near infrared emission intensities of Er(III)-encapsulated complexes were enhanced dramatically by increasing the ${\pi}$-conjugated extension of anthracene ligands. The time-resolved luminescence spectra show monoexponential decays with a lifetime of $2.0{\sim}2.4ms$ for $Er^{3+}$ ions in thin films, and calculated intrinsic quantum yields of $Er^{3+}$ ions are in the range of $0.025{\sim}0.03%$. As a result, all Er(III)-encapsulated dendrimer complexes exhibit the near IR emission with the following order: $Er^{3+}-[G3-AnD]_3$(terpy) > $Er^{3+}-[G3-AnS]_3$(terpy) ${\approx}$ $Er^{3+}-[G3-AnT]_3$(terpy), because $Er^{3+}-[G3-AnD]_3$(terpy) has a higher relatively spectral overlap J value and energy transfer efficiency. In addition, the lack of detectable phosphorescence and no significant spectral dependence of the ${\pi}$-extended anthracene moieties on the solvent polarity support energy transfer from their singlet state to the central $Er^{3+}$ ion taking place in $Er^{3+}-[G3-AnX]_3$(terpy).

• Journal of Sensor Science and Technology
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• v.6 no.1
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• pp.16-23
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• 1997

Bismuth germanate crystals well known as scintillator were grown by Czochralski method. In order to understand a mechanism of radiation resistance in Eu-doped BGO, we measured radiation induced-absorption spectra, excitation spectra, emission spectra and luminescence lifetimes of BGO crystals. We found that the charge transfer state of $Eu^{3+}$ ion is to play a key role to enhance the radiation resistance in BGO crystal. The $^{5}D_{0}$ emission of $Eu^{3+}$ ions that is not suitable for the radiation detectors due to a long decay time was found to be increased with increasing europium concentration. In the BGO crystal doped with 0.1 mole%, the density of radiation induced color centers was reduced about twenty times and the light output of $^{5}D_{0}$ was negligible by comparing to that of BGO.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.95-98
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• 2013

The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2.037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3.354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons ($D^0X$), two-electron satellite (TES), free-to-neutral-acceptors (e,$A^0$), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes' empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for $D^0X$ in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for $D^0X$ transitions.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.171.2-171.2
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• 2015

Nowadays, trivalent rare-earth ($RE^{3+}$) ions activated metal oxides have been proved to be excellent host materials due to their various applications. Facile wet-chemical technique have been considered as the best synthetic route due its intensive interest in the preparation of nanostructures. Europium ion doped lanthanum hydroxide ($La(OH)_3:Eu^{3+}$) phosphors were synthesized by the facile wet chemical method using the hexamethylenetetramine (HMTA) as a mediated surfactant. The thermal behavior for the $La(OH)_3:Eu^{3+}$ phosphors was investigated by thermogravimetric and differential thermal analysis method. The morphological studies were measured by scanning electron microscope and transmission electron microscope measurements, indicating three-dimensional (3D) flower-like $La(OH)_3:Eu^{3+}$ nanorod bundles. After subsequent annealing process, the lanthanum oxide ($La_2O_3:Eu^{3+}$) phosphor exhibited similar kind of morphology. The synthesized $La(OH)_3:Eu^{3+}$ and $La_2O_3:Eu^{3+}$ samples were characterized by X-ray powder diffraction and Fourier transform infrared spectroscopy. Furthermore, photoluminescence and cathodoluminescence properties were studied in details.

• Journal of Radiation Protection and Research
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• v.40 no.3
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• pp.147-154
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• 2015

The scatter photons and photoneutrons from high energy photon beams (more than 10 MV) will increase the undesired dose to the patient and the staff working in linear accelerator room. This undesired dose which is found at out-of-field area can increase the probability of secondary malignancy. The purpose of this study is to determine the equivalent dose of scatter photons and neutrons generated by 3 different treatment techniques: 3D-conformal, intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). The measurement was performed using two types of the optically stimulation luminescence detectors (OSL and OSLN) in the Alderson Rando phantom that was irradiated by 3 different treatment techniques following the actual prostate cancer treatment plans. The scatter photon and neutron equivalent dose were compared among the 3 treatments techniques at the surface in the out-of-field area and the critical organs. Maximum equivalent dose of scatter photons and neutrons was found when using the IMRT technique. The scatter neutrons showed average equivalent doses of 0.26, 0.63 and $0.31mSv{\cdot}Gy^{-1}$ at abdominal surface region which was 20 cm from isocenter for 3D, IMRT and VMAT, respectively. The scattered photons equivalent doses were 6.94, 10.17 and $6.56mSv{\cdot}Gy^{-1}$ for 3D, IMRT and VMAT, respectively. For the 5 organ dose measurements, the scattered neutron and photon equivalent doses in out of field from the IMRT plan were highest. The result revealed that the scatter equivalent doses for neutron and photon were higher for IMRT. So the suitable treatment techniques should be selected to benefit the patient and the treatment room staff.

• Korean Journal of Materials Research
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• v.31 no.10
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• pp.582-585
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• 2021

Y₂O₃:Eu_x (x = 0.005, 0.01, 0.02, 0.03, 0.05, 0.1 mol) phosphors are synthesized with different concentrations of Eu³⁺ ions by solvothermal method. The crystal structure, surface and optical properties of the Eu doped Y₂O₃ phosphors are investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) and photoluminescence excitation (PLE) analyses. From X-ray diffraction (XRD) results, the crystal structure of the Eu doped Y₂O₃ phosphor is found to be cubic. The maximum emission spectra of the Eu doped Y₂O₃ phosphors are observed at 0.05 mol Eu³⁺ concentration. The photoluminescence of 615 nm in the Eu doped Y₂O₃ phosphors is associated with ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The decrease in emission intensity of 0.1 mol Eu doped Y₂O₃ is interpreted by concentration quenching. The International Commission on Illumination (CIE) coordinates of 0.05 mol Eu doped Y₂O₃ phosphor are X = 0.6547, Y = 0.3374.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.184-189
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• 2013

$Ba_2SiO_4:Eu^{2+}$ ($B_2S:Eu^{2+}$) powders were prepared by firing the dry gel obtained by the sol-gel and the hybrid process (sol-gel and combustion), respectively, and their structure and luminescence were investigated. Tetraethyl orthosilicate (TEOS) was used as a Si source. The phase transition was observed with the TEOS content. With 1.2M TEOS, the powders prepared by the sol-gel process without prior calcination were composed of the $B_2S:Eu^{2+}$ single phase, whereas those by the sol-gel and the hybrid process with prior calcination consisted of the dominant $B_2S:Eu^{2+}$ and minor $BaSiO_3:Eu^{2+}$ ($BS:Eu^{2+}$) phases and their emission intensities were approximately two times higher than those without prior calcination. The hybrid process could reduce the process time innovatively compared to the sol-gel process, even though the former was a little inferior to the latter in the emission intensity of $B_2S:Eu^{2+}$. With 1.1M TEOS, the $B_2S:Eu^{2+}$ single phase was obtained by the hybrid process, and its green emission was observed at 505 nm originated from the $4f^65d^1{\rightarrow}4f^7$ transition of $Eu^{2+}$ ions.