• The Journal of Korean Academy of Prosthodontics
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• v.44 no.3
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• pp.284-294
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• 2006

Statement of problem. Proliferation of Candida albicans is primarily within the plaque on the fitting surface of the denture rather than on the inflamed mucosa. Consequently, the treatment of the denture is equally important as treatment of the tissue. Cleansing and disinfection should be efficiently carried-out as the organisms can penetrate into the voids of the acrylic resin and grow in them, from which they can continue to infect and reinfect bearing tissues. Purpose. The purpose of this study was to evaluate the applicability of photocatalytic reaction to eliminate Candida albicans from acrylic resin denture base, and to investigate the anti-fungal effect with various UVA illumination time. Materials and Methods. The specimens were cured by the conventional method following the manufacturer's instruction using thermal polymerized denture base resin (Vertex RS: Dentimex, Netherlands). $TiO_2$ photocatalyst sol(LT), which is able to be coated at normal temperature, was made from the Ti-alkoxide progenitor. The XRD patterns, TEM images and nitrogen absorption ability of the $TiO_2$ photocatalyst sol(LT) were compared with the commercial $TiO_2$ photocatalyst P-25. The experimental specimens were coated with the mixture of the $TiO_2$ photocatalyst sol(LT) and binder material (silane) using dip-coater, and uncoated resin plates were used as the control group. Crystallinity of $TiO_2$ of the specimen was tested by the XRD. Size, shape and chemical compositions were also analyzed using the FE-SEM/ EDS. The angle and methylene blue degradation efsciency were measured for evaluating the photocatalytic activity of the $TiO_2$ film. Finally, the antifungal activity of the specimen was tested. Candida albicans KCTC 7629(1 ml, initial concentration $10^5$ cells/ ml) were applied to the experiment and control group specimens and subsequently two UVA light source with 10W, 353 nm peak emission were illuminated to the specimens from 15cm above. The extracted $2{\mu}l$ of sample was plated on nutrient agar plate ($Bacto^{TM}$ Brain Heart Infusion; BD, USA) with 10 minute intervals for 120 minute, respectively. It was incubated for 24 hours at $37^{\circ}C$ and the colony forming units (CFUs) were then counted. Results. Compared the characteristics of LT photocatalyst with commercial P-25 photocatalyst, LT were shown higher activity than P-25. The LT coated experimental specimen surface had anatase crystal form, less than 20 nm of particle size and wide specific surface area. To evaluate the photocatalytic activity of specimens, methylene blue degradation reaction were used and about 5% of degradation rate were measured after 2 hours. The average contact angle was less than $20^{\circ}$ indicating that the LT photocatalyst had hydrophilicity. In the antifungal activity test for Candida albicans, 0% survival rate were measured within 30 minute after irradiation of UVA light. Conclusion. From the results reported above, it is concluded that the UVA-LT photocatalytic reaction have an antifungal effect on the denture surface Candida albicans, and so that could be applicable to the clinical use as a cleaning method.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.4
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• pp.42-49
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• 2009

This paper proposes a driving current control method for a back light unit (BLU), consisting of red, green, and blue (RGB) light-emitting diodes (LEDs), whereby an RGB optical sensor is used to check the output color stimulus variation to enable a time-stable color stimulus for light emission by the RGB LED BLU. First, to obtain the present color stimulus information of the RGB LED BLU, an RGB to XYZ transform matrix is derived to enable CIEXYZ values to be calculated for the RGB LED BLU from the output values of an RGB optical sensor. The elements of the RGB to XYZ transform matrix are polynomial coefficients resulting from a polynomial regression. Next, to obtain the proper duty control values for the current supplied to the RGB LEDs, an XYZ to Duty transform matrix is derived to calculate the duty control values for the RGB LEDs from the target CIEXYZ values. The data used to derive the XYZ to Duty transform matrix are the CIEXYZ values for the RGB LED BLU estimated from the output values of the RGB optical sensor and corresponding duty control values applied to the RGB LEDs for the present, first preceding, and second preceding sequential check points. With every fixed-interval check of the color stimulus of the RGB LED BLU, the XYZ to Duty transform matrix changes adaptively according to the present lighting condition of the RGB LED BLU, thereby allowing the RGB LED BLU to emit the target color stimulus in a time-stable format regardless of changes in the lighting condition of the RGB LEDs.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.263-272
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• 2011

Highly luminescent and monodisperse InP quantum dots (QDs) were prepared by a non-organometallic approach in a non-coordinating solvent. Fatty acids with well-defined chain lengths as the ligand, a non coordinating solvent, and a thorough degassing process are all important factors for the formation of high quality InP QDs. By varying the molar concentration of indium to ligand, QDs of different size were prepared and their absorption and emission behaviors studied. By spin-coating a colloidal solution of InP QD onto a silicon wafer, InP QD thin films were obtained. The thickness of the thin films cured at 60 and $200^{\circ}C$ were nearly identical (approximately 860 nm), whereas at $300^{\circ}C$, the thickness of the thin film was found to be 760 nm. Different contrast regions (A, B, C) were observed in the TEM images, which were found to be unreacted precursors, InP QDs, and indium-rich phases, respectively, through EDX analysis. The optical properties of the thin films were measured at three different curing temperatures (60, 200, $300^{\circ}C$), which showed a blue shift with an increase in temperature. It was proposed that this blue shift may be due to a decrease in the core diameter of the InP QD by oxidation, as confirmed by the XPS studies. Oxidation also passivates the QD surface by reducing the amount of P dangling bonds, thereby increasing luminescence intensity. The dielectric properties of the thin films were also investigated by capacitance-voltage (C-V) measurements in a metal-insulator-semiconductor (MIS) device. At 60 and $300^{\circ}C$, negative flat band shifts (${\Delta}V_{fb}$) were observed, which were explained by the presence of P dangling bonds on the InP QD surface. At $300^{\circ}C$, clockwise hysteresis was observed due to trapping and detrapping of positive charges on the thin film, which was explained by proposing the existence of deep energy levels due to the indium-rich phases.

• Journal of the Korean Electrochemical Society
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• v.2 no.4
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• pp.232-236
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• 1999

A solar cell based on dye-sensitized photoelectric conversion was studied by electrochemical and spec-trofluorometric methods for the purposes of enhancing its efficiency and stability of $TiO_2$ solar cells. Nanocrystalline $TiO_2$ was used to prepare photoelectrodes, and photosensitizing dyes such as malachite green oxalate, basic blue3, rhodamine B, and bromocresol purple were chosen as sensitizers. Electrochemical oxidation potentials and absorption and emission wavelengths of dyes were used to determine energy levels of the dyes. By comparing excited energy levels of the dyes with the conduction band edge potential $(E_{c,s})\;of\;TiO_2$ calculated by using the flat-band potential $(E_{fb})\;of\;TiO_2$, properties of a dye required to fabricate a high efficient photosensitizing solar cell with high short-circuit current $(J_{sc})$ were suggested. Enhanced stability of photocurrent was obtained by coating a $TiO_2|ITO$ electrode with Polypyrrole that Possibly Prevented the recombination between the conduction band electrons and oxidized dyes and suppressed the direct electrode redox reactions of dyes on ITO.

• 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.

• Journal of the Korean Ceramic Society
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• v.44 no.3 s.298
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• pp.147-151
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• 2007

An improvement for the efficiency of the $Sr_{2}SiO_{4}:Eu$ yellow phosphor under the $450{\sim}470\;nm$ excitation range have been achieved by adding the co-doping element ($Mg^{2+}\;and\;Ba^{2+}$) in the host. White LEDs were fabricated through an integration of an blue (InGaN) chip (${\lambda}_{cm}=450\;nm$) and a blend of two phosphors ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) in a single package. The InGaN-based two phosphor blends ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) LEDs showed three bands at 450 nm, 550 nm and 640 nm, respectively. The 450 nm emission band was due to a radiative recombination from an InGaN active layer. This 450 nm emission was used as an optical transition of the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor. As a consequence of a preparation of white LEDs using the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor yellow phosphor and CaS:Eu red phosphor, the highest luminescence efficiency was obtained at the 0.03 mol $Ba^{2+}$ concentration. At this time, the white LEDs showed the CCT (5300 K), CRI (89.9) and luminous efficacy (17.34 lm/W).

• Journal of Sensor Science and Technology
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• v.8 no.1
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• pp.10-15
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• 1999

White emission thin film electroluminescent device was fabricated using ZnS for phosphor layer and BST ferroelectric thin film for insulating layer. For fabrication conditions of BST thin film, stoichiometry of target was $Ba_{0.5}Sr_{0.5}TiO_3$, substrate temperature was $400^{\circ}C$, working pressure was 30 mTorr, and A:$O_2$ ratio was 9:1. At this time, dielectric constant was 209 at 1kHz frequency. For phosphor layer ZnS:Mn, ZnS:Tb, and ZnS:Ag were used. Mixing rates of activators were respectively 0.8, 0.8, and 1 wt%. Total thickness of phosphor tapers was 500 nm, thickness of lower insulating layer was 200 nm, and thickness of upper insulating layer was 400 nm. In this conditions, luminescence threshold voltage of thin film electroluminescent device was $95\;V_{rms}$, maximum brightness was $3,000\;cd/m^2$ at $150\;V_{rms}$. Luminescence spectrum peak was observed at region of blue(450 nm), green(550 nm), and red(600 nm).

• Journal of the Korean institute of surface engineering
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• v.39 no.3
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• pp.93-97
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• 2006

Polymer light emitting diodes (PLEDs) are expected to be commercialized as next generation displays by advantages of the fast response time, low driving voltage and easy manufacturing process for large sized flexible display. Generally, the electrical and optical properties of PLEDs are affected by the surface conditions of transparent electrode. The PLED devices with ITO/PEDOT:PSS/PVK/PFO-poss/LiF/Al structures were prepared by using the spin coating method. For this, PEDOT:PSS(poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)) Al 4083 and PVK(N-vinylcabozole) were used as hole injection and transport layers. The PFO-poss(poly(9,9-dioctylfluorene)) was used as the emitting layer. The dependence of $O_2$ plasma treatment of ITO electrode on the electrical and optical properties of PLEDs were investigated. The sheet resistances increased slightly with an improved surface roughness of ITO electrode as the RF power increased during $O_2$ plasma treatment. The PLED devices prepared on the ITO/Glass substrates, which were plasma-treated at 40 watt in RF power for 30 seconds under 40 mtorr $O_2$ pressure, showed the maximum external emission efficiency of 0.86 lm/W and the maximum luminance of $250\;cd/m^2$, respectively. The CIE color coordinates are ranged $X\;=\;0.13{\sim}0.18$ and $Y\;=\;0.10{\sim}0.16$, showing blue color. emission.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.3
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• pp.110-114
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• 2017

$NiO/NiCo_2O_4$ nanocubes were successfully synthesized via the calcination process of $Ni_3[Co(CN)_6]_2$ PBAs. The prepared monodispersed $Ni_3[Co(CN)_6]_2$ PBAs were aggregated by 'self-assembly' of the nuclei generated during the synthesis reaction. The self-assembly rate of the particles is affected by the temperature and the amount of surfactant SDBS (sodium dodecylbenzenesulfonate). FESEM analysis shows that monodispersed 200 nm PBA nanocubes are obtained at 0.25 g SDBS and $60^{\circ}C$ temperature. Thermal behavior was confirmed by thermogravimetric-differential thermal analysis (TG-DTA) to determine optimal calcination conditions. Then, field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analyzes were performed to investigate the morphology and crystallinity of the particles precursors and $NiO/NiCo_2O_4$ nanocubes.

• Journal of Radiation Protection and Research
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• v.26 no.1
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• pp.7-12
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• 2001

Sintered LiF:Mg,Cu,Na,Si thermoluminescence (TL) pellets were developed for application in radiation dosimetry. In the present study, the TL dosimetric properties of LiF:Mg,Cu,Na,Si TL pellets have been investigated for emission spectrum, dose response, energy response, and fading characteristics. LiF:Mg,Cu,Na,Si TL pellets were made by using a sintering process, that is, pressing and heat treatment from TL powders. Photon irradiations for the experiments were carried out using X-ray beams and a $^{137}Cs$ gamma source at the Korea Atomic Energy Research Institute (KAERI). The average energies and the dose were in the range of 20-662 keV and $10^{-6}-10^{-2}\;Gy$, respectively. The glow curves were measured with a manual type TLD reader(System 310, Teledyne) at a constant nitrogen flux and a linear heating rate. For a constant heating rate of $5^{\circ}C\;s^{-1}$, the main dosimetric peak of glow curve appeared at $234^{\circ}C$, the activation energy was 2.34 eV and frequency factor was $1.00{\times}10^{23}$. TL emission spectrum is appeared at the blue region centered at 410 nm. A linearity of photon dose response was maintained up to 100 Gy. The photon energy responses relative to $^{137}Cs$ response were within ${\pm}20%$ at overall photon energy region. The fading of TL sensitivity of the pellets stored at the room temperature was not found for one year.