• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.1
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• pp.27-31
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• 2011

ZnS:Mn yellow phosphors doped with Sm for white light emitting diodes were synthesized by solid state reaction method. These sample showed the characteristic X-ray diffraction patterns for main peak (110) of ZnS:Mn,Sm. Photoluminescence excitation spectra originated from $Mn^{2+}$ were ranged from 450 nm to 500 nm. The yellow emission at around 580 nm was associated with $^4T_1{\rightarrow}^6A_1$ transition of $Mn^{2+}$ ions in ZnS:Mn,Sm phosphors. The highest photolum inescence intensity of the phosphors under 405 nm and 450 nm excitation was obtained at Sm concentration of 1 mol%. The enhanced photoluminescent intensity in the ZnS:Mn,Sm phosphors was interpreted by energy transfer from Sm to Mn. The highest luminescent intensity of white LED was obtained at the epoxy-to-yellow phosphor ratio of 1:3. At this ratio, the CIE chromaticity of the white LED was X=0.3886 and Y=0.2928.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.11
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• pp.870-875
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• 2011

The $(Na_{0.52}K_{0.44})(Nb_{0.9}Sb_{0.06})O_3-0.04dLiTaO_3$ (NKNS-LT) ceramics with various $Cu_2O$ concentration were prepared by the conventional solid state reaction method. The $Cu_2O$ content was varied in the range of 0.1~0.4 wt%. The effects of Cu on microstructure, crystallographic phase transition, and piezoelectric properties were investigated. The material with perovskite structure had a tetragonal phase (T1) when $Cu_2O$ concentration was less than 0.3 wt% and it transformed to another tetragonal phase (T2) when the $Cu_2O$ amount was greater than 0.3 wt%. The phase boundary between T1 and T2 phases appeared at around 0.3 wt% of $Cu_2O$ concentration. The piezoelectric properties were shown the maximum values at the composition of the phase boundary. The electro-mechanical coupling factor ($k_p$) was 0.42 and the piezoelectric charge constant ($d_{33}$) was 245 pC/N at the 0.3 wt% of $Cu_2O$ concentration.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.321-321
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• 2008

To obtaingood resolution in PDP, one of the important factors is to achieve the accuracy of barrier ribs. The photolithographic process can be used to form patterns of barrier rib with high accuracy and a high aspect ratio. The composition for photolithography is based on the $B_2O_3-SiO_2-Al_2O_3$ glass system including additives such as alkali oxides and alkali earth oxides. The refractive index and thermal properties in glass system are changed by amount of alkali oxides and alkali earth oxides. Therefore, it is important that additives are controlled to have proper refractive index and thermal properties. The additives are contributed to non-bridging oxygen within the glass network, causing a change of density. In addition to a change of the structural cross-link density, the refractive index, dielectric and thermal properties glass are correlated with ionic radius and polarizability of cations. In this study, we investigated the refractive index and the thermal properties such as glass transition temperature, glass softening temperature and coefficient of thermal expansion by changing composition in the $B_2O_3-SiO_2-Al_2O_3$ glass system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.2
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• pp.104-108
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• 2013

In this paper, the $0.95(Na_{0.5}K_{0.5})_{0.04}[(Nb_{0.8}Ta_{0.20})_{0.994}Co_{0.015}]O_3$(abbreviated as NKNT) + $0.05KNbO_3$ lead-free piezoelectric ceramics were synthesized by the conventional mixed oxide method route with normal sintering. And also, the effects of calcination temperature on the microstructure, dielectric properties, and piezoelectric properties were investigated. A polymorphic phase transition(PPT) between orthorhombic and tetragonal phases was observed in specimens calcined at $810^{\circ}C{\sim}850^{\circ}C$. The ceramics calcined at $830^{\circ}C$ showed excellent piezoelectric properties: $d_{33}$= 179 pC/N, $k_p$= 0.384, $Q_m$= 79.73). These results indicate that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.38 no.4
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• pp.10-21
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• 2001

This paper develops a logical simulation method for by dyversity of situations. Most existing systems, for example, games and infant tutoring systems lead users to virtual environment with unfolding situations, but are not designed to induce the change of the environment itself. In this paper, a logically simulated environment is created by defining situations and single events based on situation hierarchy structure. We elaborate the occurrence of events by classifying the causality. The occurrence or natural phenomena is dictated by physical laws and natural phenomena are expressed as the transition of the event based on event association. Specifically we define the source of the event for natural phenomena and we consider the existence of objects as a primary factor in event occurrence. The advantages of this approach include the reuse of events, that is, different events can be generated in the same flow with fresh conditions. This allows us to implement a more practical and logical environment. A drawback to this method is the difficulty in dividing a situation into events. The proposed method was implemented in the context of the change of season among natural phenomena.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.4
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• pp.298-303
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• 2012

$Y_{1-x}VO_4:Eu_x^{3+}$ red phosphors were synthesized with changing the mol ratios of $Eu^{3+}$ ions by using the solid-state reaction method. The crystalline structure of phosphors was found to be a tetragonal system with the maximum diffraction intensity at $25.02^{\circ}$. The grain particles showed the truncated hexagonal patterns with a very homogeneous size distribution at 0.05 mol of $Eu^{3+}$ ion. The excitation spectra of the phosphor ceramics were composed of a broad band centered at 303 nm and weak narrow multilines peaked in the range of 360-420 nm. The dominant emission spectrum was the strong red emission centered at 619 nm due to the $^5D_0{\rightarrow}^7F_2$ electric dipole transition. The experimental results suggest that the optimum doping mol ratio of $Eu^{3+}$ ions for preparing the red phosphors is 0.10 mol with the asymmetry ratio of 5.21.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.210-211
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• 2005

[ $(K_{0.5}Na_{0.5})NbO_3$ ](KNN) 세라믹스의 소결 특성과 압전 특성을 높이기 위해 B-site에 Sb를 치환하여 Sb함량에 따른 특성을 측정 하였다. Sb 의 함량을 0mol $\sim$ 0.1mol 까지 첨가한 결과 소결 밀도는 Sb의 첨가량이 많아질수록 증가하다 Sb-0.08mol에서 4.40g/$cm^3$으로 가장 높은 밀도를 가졌으며, 여기서의 전기기계 결합 계수가(Kp) 0.45로 높은 값을 나타내었다. 상전 이 온도는 375$^{\circ}C$로 순수한 KNN 의 420$^{\circ}C$ 보다 약 45$^{\circ}C$정도 떨어졌으나 orthorhombic에 서 tetragonal 로 바뀌는 전이 온도는 KNN이 220$^{\circ}C$, KNNS 가 225$^{\circ}C$로 크게 변하지 않았다.

• Journal of the Korean Chemical Society
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• v.33 no.6
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• pp.571-576
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• 1989

The relativistically parameterized Extended Huckel (REX) calculations are carried out for $[M(NH_3)_5Cl]^{2+}$ (M = Cr, Co, Ru, Rh, Os, Ir). The calculated orbital and overlap populations agree with experimental data. The REX calculations on the electronic structure have been also compared with nonrelativistic EHT results. A ${\phi}$-bonding in M-Cl bond is founded to be more important for the $d^3$, $d^5$complexes than the $d^6$ system.

• Analytical Science and Technology
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• v.6 no.1
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• pp.39-45
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• 1993

We have examined Raman spectra of cis-peptide model complex, diketopiperazine in water and $D_2O$ with 320 nm through 218 nm excitation. Our study examines assignment of the resonance enhanced amide vibrations and characterizes their enhancement mechanism. Three resonance enhaned cis-peptide marker bands were observed in aqueous solution at 1676, 1533 and $806cm^{-1}$, which were assigned to the cis-amide I, II and S band, respectively. The $1533cm^{-1}$ amide II band, which is almost pure C-N stretching, was most dominant in water and shifted to $1520cm^{-1}$ upon N-deuteration. This band will be probably a potential probe band for cis-peptide moieties in proteins. The excitation profile data and an Albrecht A-term fit indicated that the cis-peptide vibrations derive their intensities from the 188 nm cis-peptide ${\pi}-{\pi}^*$ electronic transition. We Propose that the geometry of cis-peptide ${\pi}^*$ excited state is C-N bond displacement relative to that of electronic ground state.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.08a
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• pp.93-93
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• 2003

Photoluminescence(PL) properties of Silicon nanocrystals (nc-Si) as a function of temperature is reported to consider the mechanism of PL. Nc-Si has been made by $Si^+$ ion-implantation into thermal $SiO_2$ and subsequent annealing. And after gold had been diffused at the same samples above, the resultant PL spectra has been compared to the PL spectra from the non-gold doped nc-Si. PL peak energy variation from nc-Si is same with the variation of energy bandgap of bulk silicon as temperature changes from 6 K to room temperature. This result may mean nc-Si is still indirect transition material like bulk silicon. Gold doped nc-Si reveals short peak wavelength of PL spectrum than gold undoped one. PL peak shift through gold doing process shows clearly the PL mechanism is not from defect or interface states. PL intensity increases from 6K to a certain temperature and then decrease to room temperature. This characteristic with temperature shows that phonon have a role for the luminescence as theory explains that electron and hole can be recombined radiatively by phonon's assist in nc-Si, which is almost impossible in bulk silicon. Therefore luminescence is observed in nc-Si constructed less than a few of unit cell and the peak energy of luminescence can be higher than the bulk bandgap energy by the bandgap widening effect occurs in nanostructure.