• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2309-2314
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• 2010

Design and syntheses of four red phosphorescent heteroleptic cationic iridium(III) complexes containing two substituted phenylquinoxaline (pqx) or benzo[b]thiophen-2-yl-pyridin (btp) main ligands and one 2,2'-biimidazole (H2biim) ancillary ligand are reported: [$(pqx)_2$Ir(biim)]Cl (1), [$(dmpqx)_2$Ir(biim)]Cl (2), [$(dfpqx)_2$Ir(biim)]Cl (3), [$(btp)_2$Ir(biim)]Cl (4). Complex 1 showed a distorted octahedral geometry around the iridium(III) metal ion with cis metallated carbons and trans nitrogen atoms. The absorption, emission and electrochemical properties were systematically evaluated. The complexes exhibited red phosphorescence in the spectral range of 580 to 620 nm with high quantum efficiencies of 0.58 - 0.78 in both solution and solid-state at room temperature depending on the cyclometalated main ligands. The cyclic voltammetry of the complexes (1-3) showed a metal-centered irreversible oxidation in the range of 1.40 to 1.90 V as well as two quasi reversible reduction waves from -1.15 to -1.45 V attributed to the sequential addition of two electrons to the more electron accepting heterocyclic portion of two distinctive cyclometalated main ligands, whereas complex 4 showed a reversible oxidation potential at 1.24 V and irreversible reduction waves at -1.80 V.

• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.637-643
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• 2003

In order to improve the photoluminescent properties and crystallinity, Zn$_2$SiO$_4$:Mn, M(M=Cr, Ti) phosphors were synthesized by the sol-gel method. The willemite single phase was obtained at 110$0^{\circ}C$, which is lower temperature than that of the conventional solid-state reaction (130$0^{\circ}C$). The characteristics of fired samples were obtained by a 147 nm excitation source under VUV (Vacuum Ultraviolet). To investigation the effect of co-dopant, the content of Mn and the ratio of $H_2O$ to TEOS was fixed as 2 ㏖% and 36. 1, respectively. The highest emission intensity was obtained when the concentration of Cr and Ti was 0.1 ㏖% relative to Zn$_2$SiO$_4$:Mn. While the emission intensity decrease continuously the decay time improved as increased the Cr concentration. In the case of Ti added samples, however, the emission intensity increase up to 2 ㏖％ concentration.

• Journal of Powder Materials
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• v.23 no.2
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• pp.108-111
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• 2016

$Y_2O_3-H_3BO_3:Eu^{3+}$ powders are synthesized using a mechanical alloying method, and their photoluminescence (PL) properties are investigated through luminescence spectrophotometry. For samples milled for 300 min, some $Y_2O_3$ peaks ([222], [440], and [622]) and amorphous formations are observed. The 300-min-milled mixture annealed at $800^{\circ}C$ for 1 h with Eu = 8 mol% has the strongest PL intensity at every temperature increase of $100^{\circ}C$ (increasing from 700 to $1200^{\circ}C$ in $100^{\circ}C$ increments). PL peaks of the powder mixture, as excited by a xenon discharge lamp (20 kW) at 240 nm, are detected at approximately 592 nm (orange light, $^5D_o{\rightarrow}^7F_1$), 613 nm, 628 nm (red light, $^5D_o{\rightarrow}^7F_2$), and 650 nm. The PL intensity of powder mixtures milled for 120 min is generally lower than that of powder mixtures milled for 300 min under the same conditions. PL peaks due to $YBO_3$ and $Y_2O_3$ are observed for 300-min-milled $Y_2O_3-H_3BO_3$ with Eu = 8 mol% after annealing at $800^{\circ}C$ for 1 h.

• Applied Chemistry for Engineering
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• v.28 no.5
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• pp.571-575
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• 2017

In this study, cadmium telluride (CdTe) quantum dots were synthesized by using ultrasonic irradiation method. Optical properties and structural characteristics of the CdTe quantum dots were analyzed by two main variables; the ratio of the precursor and the synthesis time. As the synthesis time increased, the band gap reduction was observed with the growth of CdTe quantum dots. As for the luminescence properties, the red shift appeared at 510~610 nm wavelength range. Also, it was confirmed that the red shift occurs rapidly as the ratio of Te increases. According to PL peak intensity, the highest intensity was shown at 180 to 240 min. Structural characteristics of CdTe quantum dots were investigated through XRD and TEM, and the cubic zinc blend structure was observed. The size of quantum dots was about 2.5 nm and uniformly dispersed when the synthesis time took 210 min. In addition, the apparent crystallinity was discovered in FFT image.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.6
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• pp.267-272
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• 2006

A series of $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ phosphors have been synthesized by solid-state reaction. The photoluminescence and structural properties of $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ have been examined. The $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ phosphors have a strong absorption at 400 nm, which is the emission wavelength of a violet light emitting diode (LED). The emission peaks of $SrGa_2S_4:Ce,Na$are located at 448 nm and 485 nm. The partial replacement of Sr by Ca in $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ causes a red shift of emission wavelengths. The $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ can be used as blue emitting phosphors pumped by the violet LED for fabricating the multi-band white LED.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.83-88
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• 2019

LiBaPO₄:Eu²⁺ phosphors with stoichiometric and nonstoichiometric compositions were prepared using a solid state reaction followed by heat treatment in reduced atmosphere, and the crystal structures and photoluminescence(PL) properties of the powders were investigated by x-ray powder diffraction and luminescence spectrometer. At 900℃, the Ba₃(PO₄)₂ phase as the intermediate phase was observed with the LiBaPO₄ phase as the main crystalline phase. Samples with a low europium concentration at 1,000℃ belonged to the trigonal structure, whereas samples with Eu²⁺ content more than 4 mol% showed monoclinic structure. In the nonstoichiometric compositions of 4 mol% Eu²⁺ and above, a single phase of Eu²⁺-doped LiBaPO₄, showing bluish green emission, was formed.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.1-4
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• 2008

The phase transformations and luminescent properties of Eu-doped $Ca_{1-x}Sr_xAl_2O_4$ phosphors were investigated. $Ca_{1-x}Sr_xAl_2O_4:Eu^{2+}$ phosphors were synthesized by a solid-state reaction with a flux, $H_3BO_3$. A phase transformation from monoclinic $CaAl_2O_4$ to monoclinic $SrAl_2O_4$ was observed as the x values increased. A high-temperature hexagonal phase of $SrAl_2O_4$ was formed during this transformation as an intermediate phase under an $H_2$ atmosphere due to oxygen vacancies; this did not occur in an air atmosphere. Accordingly, the emission spectra shifted from a blue region to a green region as x increased.

• Korean Journal of Materials Research
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• v.18 no.2
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• pp.84-91
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• 2008

The effects of the deposition and annealing temperature on the structural, electrical and optical properties of Ag doped ZnO (ZnO : Ag) thin films were investigated. All of the films were deposited with a 2wt% $Ag_2O-doped$ ZnO target using an e-beam evaporator. The substrate temperature varied from room temperature (RT) to $250^{\circ}C$. An undoped ZnO thin film was also fabricated at $150^{\circ}C$ as a reference. The as-grown films were annealed in temperatures ranging from 350 to $650^{\circ}C$ for 5 h in air. The Ag content in the film decreased as the deposition and the post-annealing temperature increased due to the evaporation of the Ag in the film. During the annealing process, grain growth occurred, as confirmed from XRD and SEM results. The as-grown film deposited at RT showed n-type conduction; however, the films deposited at higher temperatures showed p-type conduction. The films fabricated at $150^{\circ}C$ revealed the highest hole concentration of $3.98{\times}1019\;cm^{-3}$ and a resistivity of $0.347\;{\Omega}{\cdot}cm$. The RT PL spectra of the as-grown ZnO : Ag films exhibited very weak emission intensity compared to undoped ZnO; moreover, the emission intensities became stronger as the annealing temperature increased with two main emission bands of near band-edge UV and defect-related green luminescence exhibited. The film deposited at $150^{\circ}C$ and annealed at $350^{\circ}C$ exhibited the lowest value of $I_{vis}/I_{uv}$ of 0.05.

• Journal of Radiation Industry
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• v.6 no.2
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• pp.119-123
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• 2012

The detection properties of gamma-irradiated (0~10 kGy) dried seaweed, dried shrimp, and seasoned dried filefish were investigated by photo-stimulated luminescence (PSL) and electron spin resonance (ESR). PSL could be used as a detection method on irradiated dried seaweed and dried shrimp as they showed photon counts greater than 5,000 counts/60 s (positive) in the irradiated samples with doses above l kGy. However, PSL could not be applied to detect irradiated seasoned dried filefish, because gamma-irradiated sample at 10 kGy even yielded photon counts less than 700 counts/60 s (negative). The ESR spectroscopy for only dried shrimp revealed specific signals derived from free radicals captured in the shell of shrimp. As a result, it is considered that PSL or ESR methods for detection of gamma-irradiated dried shrimp and only PSL can be used to detect gamma-irradiated seaweed. Furthermore, it is considered that hydrocarbon analysis of seasoned dried filefish containing fat by GC/MS and Thermo Luminance (TL) analysis of dried seaweed should be studied for detection of irradiation.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.386-386
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• 2012

For white light emitting diode (LED) applications, it has been reported that Y3Al5O12:Ce3+ (YAG:Ce) in nano-sized phosphor performs better than it does in micro-sized particles. This is because nano-sized YAG:Ce can reduce internal light scattering when coated onto a blue LED surface. Recently, there have been many reports on the synthesis of nano-sized YAG particles using bottom-up method, such as co-precipitation method, sol-gel process, hydrothermal method, solvothermal method, and glycothermal method. However, there has been no report using top-down method. Top-down method has advantages than bottom-up method, such as large scale production and easy control of doping concentration and particle size. Therefore, in this study, nano-sized YAG:Ce phosphors were synthesized by a high energy beads milling process with varying beads size, milling time and milling steps. The beads milling process was performed by Laboratory Mill MINICER with ZrO2 beads. The phase identity and morphology of nano-sized YAG:Ce were characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FESEM), respectively. By controlling beads size, milling time and milling steps, we synthesized a size-tunable and uniform nano-sized YAG:Ce phosphors which average diameters were 100, 85 and 40 nm, respectively. After milling, there was no impurity and all of the peaks were in good agreement with YAG (JCPDS No. 33-0040). Luminescence and quantum efficiency (QE) of nano-sized YAG:Ce phosphors were measured by fluorescence spectrometer and QE measuring instrument, respectively. The synthesized YAG:Ce absorbed light efficiently in the visible region of 400-500 nm, and showed single broadband emission peaked at 550 nm with 50% of QE. As a result, by considering above results, high energy beads milling process could be a facile and reproducible synthesis method for nano-sized YAG:Ce phosphors.