• Journal of the Microelectronics and Packaging Society
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• v.12 no.2 s.35
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• pp.155-159
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• 2005

In this report, Polymer light emitting diodes (PLEDs) with an ITO/PEDOT:PSS/MEH-PPV/Al structure were prepared by spin coating method on the glass substrate patterned ITO (indium tin oxide), using PEDOT:PSS(poly(3,4=ethylenedioxythiophene):poly(styrene sulfolnate)) as the hole transfer material and MEH-PPV(poly(2-methoxy-5-(2-ethyhexoxy)-1,4-phenylenvinylene)) having a different concentration (0.1, 0.3, 0.5, 0.7, 0.9, 1.5 wt$\%$) as the emitting material. The electrical and optical properties of the prepared PLED samples were investigated. The good electrical and optical properties were observed for the PLED samples with a MEH-PPV concentration ranging from 0.5 to $0.9 wt\%$. However, the current and luminance values for PLED sample with $1.5 wt\%$ of MEH-PPV decreased greatly. The maximum luminance and light efficiency for the PLEDs with concentration of $0.5 wt\%$ MEH-PPV were $409 cd/m^2$ and 4.90 Im/W at 9 V, respectively. The emission spectrums were found to be $560{\~}585 nm$ in wavelength showing orange color.

• Korean Journal of Optics and Photonics
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• v.28 no.3
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• pp.116-121
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• 2017

In this paper, a Raman spectrometer is designed to detect chemicals contaminating the ground. The system is based on Raman spectroscopy, which is spectral analysis of scattered light from chemicals, induced by a laser. The system consists of a transmitting-optics module with a laser to induce Raman-scattered light from the sample, a receiving-optics module to collect the scattered light, and a spectrograph to separate the collected light into a wavelength spectrum. The telescope, a part of the receiving-optics module, is designed to produce a focal spot in the same position for variable measurement distances using the code V simulator, considering the distance change between the system and the road. The Raman spectra of 12 chemicals on a glass surface and on a concrete sample were measured. Intensity differences between the Raman spectra acquired on a glass surface and on a concrete sample were observed, but the characteristics of the spectra according to the chemicals on them were similar. Additionally, the Raman spectrum of PTFE (polytetrafluoroethylene) was measured at various distances. The measured and simulated optical throughputs were similar. In conclusion, it is confirmed that with this system the Raman spectrum can be measured, irrespective of the distance change.

• Journal of Korean Academy of Oral Health
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• v.41 no.4
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• pp.290-295
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• 2017

Objectives: Dental plaque emits red fluorescence under a visible blue light near the ultra-violet end of the light spectrum. The fluorescence characteristics of each microorganism have been reported in several studies. The aim of this study was to evaluate changes in red fluorescence of oral microorganisms that is affected by blood in the culture media. Methods: The gram-positive Actinomyces naeslundii (AN, KCTC 5525) and Lactobacillus casei (LC, KCTC 3109) and gram negative Prevotella intermedia (PI, KCTC 3692) that are known to emit red fluorescence were used in this study. Each bacterium was activated in broth and cultivated in different agar media at $37^{\circ}C$ for 7 days. Tryptic soy agar with hemin and vitamin $K_3$ (TSA), TSA with sheep blood (TSAB), basal medium mucin (BMM) medium, and BMM with sheep blood (BMMB) were used in this study. Fluorescence due to bacterial growth was observed under 405-nm wavelength blue light using the quantitative light-induced fluorescence-digital (QLF-D) device. The red, green, and blue fluorescence values of colonies were obtained using image-analysis software and the red to green ratio (R/G value) and red to total RGB ratio (R/RGB value) were calculated for quantitative comparison. Results: The QLF-D images of the AN, LC, and PI colonies showed red fluorescence in all media, but the fluorescence of all bacteria was reduced in TSA and BMM media, compared with in TSAB and BMMB media. Both the R/G and the R/RGB values of all bacteria were significantly reduced in growth media without blood (P<0.001). Conclusions: Based on this in vitro study, it can be concluded that red fluorescence of oral bacteria can be affected by growth components, especially blood. Blood-containing medium could be a significant factor influencing red fluorescence of oral bacteria. It can be further hypothesized that bleeding in the oral cavity can increase the red fluorescence of dental plaque.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.3
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• pp.78-82
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• 2023

A fabrication of smart windows with controllable visible light transmittance in three steps by using λ/2 retardation films based on a reactive mesogen (RM) material and polarizing films is demonstrated. The phase retardation films with a Δn·d value of λ/2 (λ: wavelength) convert the direction of a traveling light to the optical axis of the film symmetrically. In this work, the retardation characteristics according to the RM thickness were evaluated and henceλ/2 phase retardation film can be fabricated. The phase retardation film with Δn·d of 276.1 nm, which is close to λ/2 (=275 nm @550 nm), was fabricated. The light transmittance of a smart window with the structure of (polarizing film)/(glass)/(alignment layer)/(λ/2 retardation film) was measured in the transmission mode, half mode and blocking mode. The evaluation results show that the transmittance of the smart window can be controlled in three steps with 35.8%, 27.8%, and 18.2% at each mode, respectively. In addition, by fabricating a smart window with a size of 15×200 mm², the feasibility of use in various fields such as buildings and automobiles was verified.

• Journal of dental hygiene science
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• v.14 no.3
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• pp.319-324
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• 2014

The aim of this study was to evaluate influences of titanium dioxide ($TiO_2$) concentrations and irradiation times on growth of Streptococcus mutans when irradiated by visible light (405 nm wavelength) and by ultraviolet light (254 nm wavelength). To find the optimal antibacterial concentration of $TiO_2$, 0.01, 0.1, 1.0, and 10.0 mg/ml $TiO_2$ suspension was prepared with sterilized distilled water. S. mutans cultured media was added to $TiO_2$ solution to set the final cell count to $10^4CFU/ml$. The photocatalytic reaction was induced by irradiating 254 nm and 405 nm lights for 10 minutes. To compare the bactericidal activities according to irradiation times, all photocatalytic reaction was carried out with 0.1 mg/ml $TiO_2$ for 0, 10, 20, 30, and 40 minutes with both lights. After the photocatalytic reaction, $100{\mu}m$ of the reaction mixture was immediately plated on brain heart infusion agar. These plates were placed at 5% $CO_2$, $37^{\circ}C$, for 24 hours and the bacterial colonies were counted. All experiments were performed in quintuplicate. One-way ANOVA was used to determine whether there were any significant differences between the $TiO_2$ concentrations or the irradiation times. The most effective concentration of $TiO_2$ for its photocatalytic bactericidal effect on S. mutans was 0.1 mg/ml when irradiated with 254 nm and 405 nm lights. The longer the irradiation time, the bigger the bactericidal effect for both wavelengths. Over 99% of bacteria in the inoculum were killed after irradiation with 254 nm for 20 minutes and with 405 nm for 40 minutes. In conclusion, a photocatalytic reaction of $TiO_2$ induced by visible light of 405 nm constitutes the bactericidal effect on S. mutans.

• Journal of Photoscience
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• v.9 no.2
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• pp.436-438
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• 2002

Since solar radiation contains wavelength essential for photosynthesis accompanying with near-UV light, UV-B effects on biological parameters and acclimation mechanisms are influenced by photosynthetically active radiation (PAR). Therefore, to elucidate near-UV shielding mechanism in higher plants, we cultivated cauliflower under usual solar radiation and increased UV-B from fluorescent lamps, two- or three-fold excess over continuously estimated UV-B dose in PAR during daytime, using computer regulated systems. Increased UV-B radiation had little effect on growth expressed as fresh weigh and leaf area. Water soluble low molecular weight compounds showing absorption in near UV region were enhanced according to the irradiated UV-B dose. One of compounds in cauliflower leaves was identified as chlorogenic acid. This was found to have no near-UV photosenSitizerable activity and is known to have an ability to scavenge a wide species of active oxygen. Another pro-oxidant compound that generates superoxide anion radical under near-UV irradiation was not induced by increased UV-B during cultivation, and identified as lumazine, a degradation product from folic acid.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.465-472
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• 1997

An extension of new test methods for surfaces with an apparatus based on photon-induced desorption and ionisation in the electric field, is constructed and tested, It also investigates how to show the efficiency of the arrangement adsorbates $H_2$ and He on W(110). The field emitter temperature was 80 K. The wavelength of light used was 193 nm with field strengths between 10 and 50 V/nm. Many ion fragments($CO^+, He^+, H_2^^+, H_2O^+, W^{3+}\; and\; W^{2+}$) were produced by an electronic stimulation of the adsorbate with the help of a photon energy of 6.4 eV at He and $H_2$/W(110). A transient recorder enables the registration of the entire mass spectrum.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1703-1705
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• 2004

New luminescent material, 6.11-dihydoxy-5.12-naphtacene-dione $Alq_3$ complex($Alq_2$-Ncd), 1.4-dihydoxy-5.8-naphtaquinone $Alq_3$ complex ($Al_2Nq_4$) was synthesized. The $Alq_2-$ Ncd and $Al_2Nq_4$ has big molecular weight and many ${\pi}$-electrons more than widely known $Alq_3$. And extended efforts have been made to obtain high-performance electro luminescent(EL) devices. We used hole transfer layer of powdered TPD to improve hole transfer and characteristics of interface in OLED. This study indicates not only the sterical effect but also some other effects that would be responsible for the change of the emission wavelength. improvement of luminance and etc.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.359-359
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• 2012

Trivalent rare-earth ($RE^{3+}=Eu^{3+}\;and\;Tb^{3+}$) ions activated $CaGd_4O_7$ phosphors were synthesized by a sol-gel process. After annealing at $1,500^{\circ}C$, the XRD patterns of the phosphor confirmed their monoclinic structure. The photoluminescence excitation spectra of $Eu^{3+}$ and $Tb^{3+}$ doped $CaGd_4O_7$ phosphor shows the broad-band excitations in the shorter wavelength region due to charge transfer band of completely filled $O^{2-}$ to the partially filled $Eu^{3+}$ ions and f-d transitions of $Tb^{3+}$ ions, respectively. The photoluminescence spectra show that the reddish-orange ions and green emission for $Eu^{3+}$ and $Tb^{3+}$ ions, respectively. Owing to the importance of thermal quenching property in the technological parameters, the temperature-dependent luminescence properties of these phosphors were measured for examing the suitability of their applications in the development of light emitting diodes (LEDs). In addition to those measurements, the cathodoluminescence properties were examined by changing the acceleration voltage and filament current. The calculated chromaticity coordinates of these phosphors were close proximity to those of commercially available phosphors for LED and field emission display devices.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.2041-2044
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• 2004

A pyroelectric sensor using $PbTiO_3$/P(VDF/TrFE) nanocomposites thin film for sensing materials has been fabricated and evaluated with other commercial pyroelectric sensors that use ceramic materials for sensing. The device was mounted in a TO-5 housing to detect infrared light of 5.5 ~ 14 ${\mu}m$ wavelength. The NEP (noise equivalent power) and specific detectivity D of the device were 1.30 ${\times}$ $10^{-8}$W and 1.53 ${\times}$ $10^7$cm /W respectively under emission energy of 13 ${\mu}$W/c$m^2$ respectively. This result shows a better characteristic than the other commercial pyroelectric infrared sensors.