• Korean Journal of Materials Research
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• v.26 no.10
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• pp.577-582
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• 2016

$Dy^{3+}$ and $Eu^{3+}$-codoped $SrWO_4$ phosphor thin films were deposited on sapphire substrates by radio frequency magnetron sputtering by changing the growth and thermal annealing temperatures. The results show that the structural and optical properties of the phosphor thin films depended on the growth and thermal annealing temperatures. All the phosphor thin films, irrespective of the growth or the thermal annealing temperatures, exhibited tetragonal structures with a dominant (112) diffraction peak. The thin films deposited at a growth temperature of $100^{\circ}C$ and a thermal annealing temperature of $650^{\circ}C$ showed average transmittances of 87.5% and 88.4% in the wavelength range of 500-1100 nm and band gap energy values of 4.00 and 4.20 eV, respectively. The excitation spectra of the phosphor thin films showed a broad charge transfer band that peaked at 234 nm, which is in the range of 200-270 nm. The emission spectra under ultraviolet excitation at 234 nm showed an intense emission peak at 572 nm and several weaker bands at 479, 612, 660, and 758 nm. These results suggest that the $SrWO_4$: $Dy^{3+}$, $Eu^{3+}$ thin films can be used as white light emitting materials suitable for applications in display and solid-state lighting.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.97-97
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• 2010

We demonstrate the hybrid polymer-quantum dot based multi-functional device (Organic bistable devices, Light-emitting diode, and Photovoltaic cell) with a single active-layer structure consisting of CdSe/ZnS semiconductor quantum-dots (QDs) dispersed in a poly N-vinylcarbazole (PVK) and 1,3,5-tirs- (N-phenylbenzimidazol-2-yl) benzene (TPBi) fabricated on indium-tin-oxide (ITO)/glass substrate by using a simple spin coating technique. The multi-functionality of the device as Organic bistable device (OBD), Light Emitting Diode (LED), and Photovoltaic cell can be successfully achieved by adding an electron transport layer (ETL) TPBi to OBD for attaining the functions of LED and Photovoltaic cell in which the lowest unoccupied molecular orbital (LUMO) level of TPBi is positioned at the energy level between the conduction band of CdSe/ZnS and LiF/Al electrode (band-gap engineering). Through transmission electron microscopy (TEM) study, the active layer of the device has a p-i-n structure of a consolidated core-shell structure in which semiconductor QDs are uniformly and isotropically adsorbed on the surface of a p-type polymer core and the n-type small molecular organic materials surround the semiconductor QDs.

• Solar Energy
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• v.12 no.3
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• pp.10-20
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• 1992

In this experiment, photochemical reaction has been applied to destroy TCE in water phase. The main target of this work is to investigate the technical feasibility of large scale of solar detoxification reactor for water treatment. The results have revealed that solar detoxification utilizing photon energy from the sun is the most attractive process to decompose organic toxins in water phase at room temperature. The detailed results from this work are as follows; (1) The highest conversion ratio of TCE was obtained by using $TiO_2$, annatase as a photocatalyst among $TiO_2$ anatase, $TiO_2$ rutile and $V_2O_5$ under the same experimental condition. The anatase crystal structure was confirmed with XRD analysis, and its surface area was 7.748 $m^2/g$ from the BET-$N_2$ measurement (2) 0.1 wt% of $TiO_2$ anatase has been adopted as optimal quantity for batch slurry reactor at this experimental conditions. (3) The effect of hydrogen peroxide on the conversion of TCE was investigated. Its optimal quantity was 0.06 vol. % under this experimental conditions. (4) The effect of oxygen on the conversion of TCE also was studied by controlling the head space in photoreactor. Results indicated that sufficient amount of oxygen should be supplied to accomplish the highest conversion rate of TCE in water phase.

• Journal of Magnetics
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• v.11 no.1
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• pp.12-15
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• 2006

Magnetic and electronic properties of reduced rutile titanium dioxide $(TiO_{2-\delta})$ thin films doped by Mn have been investigated. The present sol-gel-grown semiconducting $TiO_{2-\delta}:Mn$ films exhibit a ferromagnetic behavior at room temperature for a limited range of Mn content. The Mn-doped films have p-type electrical conductivity with the carrier concentration near $10^{19}\;cm^{-3}$. The observed room-temperature ferromagnetism is believed to be intrinsic but not related to free carriers such as holes. Oxygen vacancies are likely to contribute to the room-temperature ferromagnetism-trapped carriers in oxygen vacancies can mediate a ferromagnetic coupling between neighboring $Mn^{+3}$ ions. The energy band-gap change due to the Mn doping measured by spectroscopic ellipsometry exhibits a red-shift compared to that of the undoped sample at low Mn content. It is explainable in terms of strong spin-exchange interactions between Mn ion and the carrier.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1451-1456
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• 2012

A novel tetrathiafulvalene (TTF)-based main-chain polymer (6TTF-polymer) was successfully synthesized via a condensation polymerization between a newly synthesized dihydroxy TTF derivative and a malonyl chloride, and its chemical structure was characterized by spectroscopic techniques. Molecular weight of the 6TTF-polymer (9,030 g/mol by gel permeation chromatography) was large enough to form the ductile film. The electrochemical and optical properties of the 6TTF-polymer were further estimated by cyclic voltammetry, ultraviolet and photoluminescence spectroscopes. The highest occupied molecular orbital level ($E_{HOMO}$=-4.79 eV) and band-gap energy ($E_g$=1.91 eV) of the 6TTF-polymer suggested that TTF-based polymer could act as a good electron donating material for the optoelectronic applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.984-989
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• 2012

We have investigated the structural, electrical and optical properties of Ga-doped ZnO (GZO) thin films prepared by RF magnetron sputtering with laboratory-made ZnO targets containing 1, 3, 5, 7 wt% of $Ga_2O_3$ powder as a doping source. The GZO thin films show the typical crystallographic orientation with c-axis regardless of $Ga_2O_3$ content in the targets. The $3,000{\AA}$ thick GZO thin films with the lowest resistivity of $7{\times}10^{-4}{\Omega}{\cdot}cm$ are obtained by using the GZO ($Ga_2O_3$= 5 wt%) target. Optical transmittance of all films shows higher than 80% at the visible region. The optical energy band gap for GZO films increases as the carrier concentration ($n_e$) in the film increases.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.49.2-49.2
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• 2010

Polycrystalline CdTe thin films for solar cell continues to be a promising material for the development of cost effective and reliable photovoltaic processes. The two key advantages of this material are its high optical absorption coefficient and its near ideal band gap for photovoltaic conversion efficiency of 1.4-1.5 eV. In this study we made the CdTe thin films for solar cell application which was deposited on the glass substrates using a modified chemical spray method at low temperature. This process does not require the sophisticated and expensive vacuum systems. The prepared CdTe films were characterized with the aid of scanning electron microscope (SEM), UV-visible spectrophotometer, and X-ray diffraction spectrometer (XRD). Following are results of a study on the "Human Resource Development Center for Economic Region Leading Industry" Project, supported by the Ministry of Education, Science & Tehnology(MEST) and the National Research Foundation of Korea(NRF).

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.226-226
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• 2012

The electronic and electrical properties of nickel oxide (NiO) thin films were investigated by reflection electron energy loss spectroscopy (REELS), x-ray photoelectron spectroscopy (XPS), and Hall Effect measurements. REELS spectra revealed that the band gap of the NiO thin film was increased from 3.50 eV to 4.02 eV after annealing the sample at $800^{\circ}C$. Our XPS spectra showed that the amount of Ni2O3 decreased after annealing. The Hall Effect results showed that the doping type of the sample changed from n type to p type after annealing. The resistivity decreased drastically from $4.6{\times}10^3$ to $3.5{\times}10^{-2}$ ${\Omega}{\cdot}cm$. The mobility of NiO thin films was changed form $3.29{\times}10^3$ to $3.09{\times}10^5cm^2/V{\cdot}s$. Our results showed that the annealing temperature plays a crucial role in increasing the carrier concentration and the mobility which leads to lowering resistivity of NiO thin films.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3383-3386
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• 2012

SnS thin films were deposited on glasses through metal organic chemical vapor deposition (MOCVD) method at relatively mild conditions, using bis(3-mercapto-1-propanethiolato) tin(II) precursor without toxic $H_2S$ gas. The MOCVD process was carried out in the temperature range of $300-400^{\circ}C$ and the average grain size in fabricated SnS films was about 500 nm. The optical band gap of the SnS film was about 1.3 eV which is in optimal range for harvesting solar radiation energy. The precursor and SnS films were characterized through infrared spectroscopy, nuclear magnetic resonance spectroscopy, DIP-EI mass spectroscopy, elemental analyses, thermal analysis, X-ray diffraction, and field emission scanning electron microscopic analyses.

• Bulletin of the Korean Chemical Society
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• v.34 no.9
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• pp.2737-2740
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• 2013

The layered $KTiNbO_5$ was successfully synthesized with titanium(IV) isopropoxide and niobium oxalate by a novel polymerized complex (PC) method. The morphology and structure of the as-prepared sample was characterized by means of High-Resolution Transmission Electron Microscope, powder X-ray diffraction, and Laser Raman Spectroscopy. The spectral response characteristic was recorded by using UV-vis Diffuse Reflectance Spectroscopy. Results show that $KTiNbO_5$ as-prepared by PC method presents an uniform morphology of nano-particles, the mean particle sizes is ca. 28 nm corresponding to the (002), and the crystal structure can be well indexed to the orthorhombic phase. The sample as-prepared by PC method has higher band gap energy than that of the sample prepared by a solid-state reaction method due to the quantum size effect.