• Journal of the Korean Ceramic Society
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• v.42 no.6 s.277
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• pp.377-383
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• 2005

Generally, the strength achieved of glass-ceramics is higher as is the fracture toughness, as compared with the original glass. This improvement is due to the microstructure consisting of very small crystals. In this study, Ag-doped $45SiO_2-24CaO-24Na_2O-4P_2O_5$ glasses were irradiated to strengthen by the crystallization using Femto second laser Pulses. Through the UV/VIS spectroscope, XRD, Nano-indenter and SEM etc., heat-treated and irradiation of laser pulses without heat-treated samples were analyzed. Two kinds of samples, heat-treated and laser irradiated without heat-treated samples, showed the peaks in the same wavelength near 360 nm. Especially, samples irradiated by 140 mW laser with XYZ stage having at the rate of 100$\~$l000 $\mu$m/s had the largest absorption peak among them, and heat-treated samples was shown lower absorption range than over 90 mW laser irradiated samples. Moreover, samples irradiated by laser had higher values ($4.4\~4.56{\times}10^{-3}(Pa)$) of elastic modulus which related with strength of glass than values of heat-treated samples and these are 1.2$\~$1 .5 times higher values than them of mother glass.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.311-316
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• 2015

This paper presents a design method for thin but wideband absorbers using resistive sheets. Its equivalent circuit consists of a series RLC resonant circuit and a short-terminated transmission line. Based on this equivalent circuit, we presented the three conditions for an electromagnetic absorber which has a thickness less than a quarter wavelength and wide absorption bandwidth at center frequency. By using an root-finding algorithm, the equivalent resistance, capacitance, and inductance of the absorbers are obtained. These equivalent circuit values for the absorber surface can be realized by a 2D periodic cross-shaped structure which has required surface resistance. Using the design method, we have designed the absorber which has 18.75 mm($67.5^{\circ}$ electrical length) thickness and 90 % absorption bandwidth of 116 % bandwidth at 3 GHz.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.1
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• pp.35-40
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• 2015

In this study, an n-ZnO/p-Si heterojunction diode with embedded Ag nanoparticles was fabricated to investigate the possible improvement of light trapping via the surface plasmon resonance effect for solar cell applications. The Ag nanoparticles were fabricated by the physical sputtering method. The acquired current-voltage curves and optical absorption spectra demonstrated that the application of Ag nanoparticles in the n-ZnO/p-Si interface increased the photo current, particularly in specific wavelength regions. The results indicate that the enhancement of the photo current was caused by the surface plasmon resonance effect generated by the Ag nanoparticles. In addition, minority carrier lifetime measurements showed that the recombination losses caused by the Ag nanoparticles were negligible. These results suggest that the embedding of Ag nanoparticles is a powerful method to improve the performance of n-ZnO/p-Si heterojunction solar cells.

• Korean Journal of Materials Research
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• v.22 no.3
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• pp.140-144
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• 2012

Compared with bulk material, quantum dots have received increasing attention due to their fascinating physical properties, including optical and electronic properties, which are due to the quantum confinement effect. Especially, Luminescent CdSe quantum dots have been highly investigated due to their tunable size-dependent photoluminescence across the visible spectrum. They are of great interest for technical applications such as light-emitting devices, lasers, and fluorescent labels. In particular, quantum dot-based light-emitting diodes emit high luminance. Quantum dots have very high luminescence properties because of their absorption coefficient and quantum efficiency, which are higher than those of typical dyes. CdSe quantum dots were synthesized as a function of the synthesis time and synthesis temperature. The photoluminescence properties were found strongly to depend on the reaction time and the temperature due to the core size changing. It was also observed that the photoluminescence intensity is decreased with the synthesis time due to the temperature dependence of the band gap. The wavelength of the synthesized quantum dots was about 550-700 nm and the intensity of the photoluminescence increased about 22~70%. After the CdSe quantum dots were synthesized, the particles were found to have grown until reaching a saturated concentration as time increased. Red shift occurred because of the particle growth. The microstructure and phase developments were measured by transmission electron microscopy (TEM) and X-ray diffractometry (XRD), respectively.

• Advances in nano research
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• v.3 no.3
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• pp.133-141
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• 2015

Influence of Ag nanoparticles on optical and photovoltaic properties of, silicon substrates, silicon solar cells and glass have been investigated. Silver nanoparticles have been fabricated by evaporation of thin Ag layers followed by the thermal annealing. The surface plasmon resonance peak was observed in the absorbance spectrum at 470 nm of glass with deposited silver nanoparticles. It is demonstrated that deposition of silver nanoparticles on silicon substrates was accompanied with a significant decrease in reflectance at the wavelength 360-1100 nm and increase of the absorption at wavelengths close to the band gap for Si substrates. We studied influence of Ag nanoparticles on photovoltaic characteristics of silicon solar cells without and with common use antireflection coating (ARC). It is shown that silver nanoparticles deposited onto the front surface of the solar cells without ARC led to increase in the photocurrent density by 39% comparing to cells without Ag nanoparticles. Contrary to this, solar cells with Ag nanoparticles deposited on front surface with ARC discovered decrease in photocurrent density. The improved performance of investigated cells was attributed to Ag-plasmonic excitations that reduce the reflectance from the silicon surface and ultimately leads to the enhanced light absorption in the cell. This study showed possibility of application of Ag nanoparticles for the improvement of the conversion efficiency of waferbased silicon solar cells instead of usual ARC.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.4
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• pp.180-183
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• 2001

$YVO_{4}$ and Nd:$YVO_{4}$ single crystals have been grown developed Edge-defined film-fed growth (EFG) method and the crystals were measured on optical properties. $YVO_{4}$ and Nd:$YVO_{4}$ single crystal were transparent, high quality due to homogeneity of surface temperature of the melt and stability of meniscus during crystal growth. In transmittance and absorption spectra, Nd:$YVO_{4}$ single crystals had absorption peaks at wavelengths of 532, 593, 753, 808, 888 though $YVO_{4}$ single crystal had a broad transmittance at wavelength ranging from 340 to 1000nm. Also, Nd:$YVO_{4}$ single crystals had emissions of energy at range of 800~900 nm in photoluminescence (PL) spectrum.

• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.695-702
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• 1994

Current study was undertaken to explain the structural evolution and corresponding changes in the properties of calcium aluminate glasses with the variation of SiO2 doping concentration. Calcium aluminate glasses in the compositional ranges of (100-x)(0.6CaO+0.4Al2O3)+xSiO2(where x=0~60) were fabricated. DTA analysis confirmed an anomalous behavior in glass transition temperature (Tg) with the maximum of 887$^{\circ}C$ and minimum of 859$^{\circ}C$ when x=5 and 50, respectively. densities and refractive indices monotonically decreased with increasing SiO2 content and IR transmitting cutoff shifted to shorter wavelength side when the amount of added SiO2 exceeded 5 mole%. IR fundamental vibration absorption peaks showed the change that NBOs were inclined to SiO4 tetrahedron in the low-silica region and NBO per SiO4 tetrahedra changed from 2 to 0 with increasing silica content. Based on the analysis of IR fundamental vibration absorption peaks, the model of the structural change can be proposed in three step: 1) SiO4 scavenged the NBOs located at AlO4-tetrahedra, which resulted in the increased of Tg values, 2) NBOs located in the main network again with a decrease in Tg, and 3) dominated by the decrease in the relative amount of NBOs in the glass system, where Tg re-increased.

• Journal of the Korean Ceramic Society
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• v.11 no.2
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• pp.3-10
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• 1974

For the manufacture of the silver-yellow glass, silver nitrate was used as a colorant in the base glass of $K_2O$-CaO-$SiO_2$ system. The latter in which the optimum condition was revealed showing beautiful yellow color had been selected among others after the preparatory studies to choose base glass. Other base glass systems considered were $Na_2O$-CaO-$SiO_2$, $R_2O$-PbO-$SiO_2$ and $R_2O$-PbO-BaO-$SiO_2$. The color developed on the specimen in various conditions was examined, using spectorphotometer, in term of the changes in absorbance with wavelength in the visible range. Experimental variables were the amount of the colorant and the additives, reheating temperature and time. The additives such as ZnO, BaO, $B_2O_3$ and $As_2O_3$ were added to increase the coloring action. It was observed that as the amount of silver increased in the base glass the absorbance around $410{\mu}m$ showed the increasing tendency, but the width of absorption curve was wider. Hence, the optimum amount of silver appeared to be 0.11~0.12%. It was found that ZnO was effective additive when present about 0.1%, while $As_2O_3$ ineffective rather retarding the coloration. Borax and $BaCO_3$ were proved effective when contained separately, but appeared ineffective when coexisted. Proper reheating temperature and time was ranged 550~$580^{\circ}C$ and 50~60 minutes. The higher the reheating temperature and the longer the reheating time, the absorbance was increased, while the width of absorption curve was wider. The colored glass prepared in the present experimental condition was found to have good water-resistance for the decorative purpose.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.821-826
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• 2008

Nanocrystallized glasses with the composition of $(50-x)BaO-xTiO_2-50SiO_2$ (x=10, 15, 16.7 and 20) have been prepared by heat-treatment at $T_x$ (crystallization onset temperature) for 3 h, and their optical properties, photoluminescence (PL), XRD and Raman spectra have been examined. The absorption edges of the glasses were red-shifted and the absorption coefficient increased with an increase of $TiO_2$. The glass subjected to the heat-treatment showed a dense formation of ${Ba_2}{TiSi_2}{O_8}$ crystals. The XRD and Raman results show that the nanocrystallized glasses formed fresnoite phase up to $TiO_2$ concentrations of 15 mol%. Further-more, blue luminescence with a peak at the wavelength of around 470nm was observed in the nanocrystallized glass, demon strating the optical multifunctional nanocrystallized material such as non-linear optics and photo-luminescence. It is thought that the blue luminescence from the ${Ba_2}{TiSi_2}{O_8}$ nanocrystallized glass originated from the presence of $Ti^{4+}$ incorporated into the fresnoite-type structure.

• Fashion & Textile Research Journal
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• v.16 no.3
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• pp.492-498
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• 2014

Lotus(Nelumbo nucifera gaertn) is intimate plant to many people that it has clean and noble characteristics despite growth in the mud. Especially Lotus seedpods, byproduct of lotus, are rich in oligometric procyanidins and could be a new source of procyanidins. Procyanidins, also known as condensed tannins, are a class of polyphenols. In other words lotus seedpod contains plenty of tannins. Commonly tannins colorants could increase adsorption and fastness properties in fabric dyeing. This study was made to investigate colorants characteristics of lotus seedpod and various colorfastness properties of dyed silk fabrics. The wavelength of maximum absorption of lotus seedpod solution appeared at 273.5 nm from UV-vis spectrophotometer. From the results of FT-IR spectra measurements, IR absorption band of lotus seedpod colorants appeared at $3415cm^{-1}$, $2900cm^{-1}$ and $1620cm^{-1}$ by tannin structure. And tannin ingredient contents was the highest at pH 9 and flavonoid at pH 11. Lotus seedpod colorants showed relatively good affinity at pH 3 on silk fabrics and optimum dyeing temperature and time for silk was for 50 min, at $80^{\circ}C$. K/s of Light fastness according to different washing method was the highest at process including ironing and ${\Delta}E$ was the lowest. All of fastness(Light rubbing laundering perspiration dry cleaning) showed excellent results over 4 or 4-5 grades.