갈륨 K 흡수단의 저온 EXAFS를 이용한 PbO-Ga$_2$O$_3$ 유리의 구조 해석

최용규,김경헌,허종,Choi, Yong-Gyu,Kim, Kyong-Hon,Chernov, Vladimir A,Heo, Jong 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.11

Ga K-edge EXAFS spectra of PbO-Ga2O3 glasses were recorded at liquid nitrogen temperature and analyz-ed in order to quantitatively understand the medium-range-order arrangement around gallium in the glasses. The second peak was generated from a backscattering of the neighbor balliums and the Ga-Ga distance is ~3.13 A with Ga coordination number of ~2.7 Therefore GaO4 tetrahedra are connected through the cor-ner~sharing mode and form their own clusters made of the tetrahedra sharing more than 3 corners while some chains or rings are also present. These connection schemes of the GaO4 tetrahedra are believed to form the substantial part of the network structure.

$GeO_2$의 첨가가 $PbO-Bi_2O_3-Ga_2O_3$ 유리의 안정화에 미치는 영향

최용규,허종,류선윤,Choi, Yong-Gyu,Heo, Jong,Ryou, Sun-Youn 한국세라믹학회 1995 한국세라믹학회지 Vol.32 No.11

Effects of GeO2 addition on the thermal and structural stabilities of PbO-Bi2O3-Ga2O3 glasses were studied. Thermal stabilities, as assessed by the weighted thermal stability factors [(Tx-Tg)/Tg], increased with GeO2 concentraton from 0.097 to 0.210 with the addition of 20 mol% GeO2. Increasing GeO2 content resulted in the decrease of apparent density, molar volume, refractive index and thermal expansion. On the other hand, IR transmission cut-off (λT=50%) moved from 6.73${\mu}{\textrm}{m}$ for the ternary PbO-Bi2O3-Ga2O3 glass to shorter wavelength side, 5.98${\mu}{\textrm}{m}$ for a glass containing 20mol% GeO2. There were little change with GeO2 content, however, in the activation energies for the viscous flow of approximately 140 kcal/mole within the temperature interval of 300~50$0^{\circ}C$. Addition of GeO2 to PbO-Bi2O3-Ga2O3 glasses enhanced the thermal and structural stabilities significantly at the expense of their infrared transmittance. An appropriate compsomise between these two opposite trends should be made following the specifications of the final applications.

희토류 첨가 광소재의 나노구조 : Dy 첨가 Ge-As-S 유리의 X-선 흡수 스펙트럼 분석

최용규,송재혁,신용범,허종,Choi, Yong-Gyu,Song, Jay-Hyok,Shin, Yong-Beom,Chernov, Vladimir A.,Heo, Jong 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.3

Dy $L_3$-edge XANES and EXAFS spectra of chalcogenide Ge-As-S glass doped with ca. 0.2 wt% dysprosium have been investigated along with some reference Dy-containing crystals. Amplitude of the white-line peak in XANES spectrum of the glass sample turns out to be stronger than that of other reference crystals, i.e., $DY_2S_3,\;Dy_2O_3\;and\;DyBr_3$. It has been verified from the Dy $L_3$-edge EXAFS spectra that a central Dy atom is surrounded by $6.7{\pm}0.5$ sulfur atoms in its first coordination shell in the Ge-As-S glass, which is relatively smaller than 7.5 of the $Dy_2S_3$ crystal. Averaged Dy-S inter-atomic-distance of the glass ($2.78{\pm}0.01{\AA}$) also turns out to be somewhat shorter than that of the $Dy_2S_3$ crystal ($2.82{\pm}0.01{\AA}$). Such nanostructural changes occurring at Dy atoms imply there being stronger covalency of Dy-S chemical bonds in the Ge-As-S glass than in the crystal counterpart. The enhanced covalency in the nanostructural environment of $Dy^{3+}$ ions inside the glass would then be responsible for optical characteristics of the $4f{\leftrightarrow}4f$ transitions of the dopants, i.e., increase of oscillator strengths and spontaneous radiative transition probabilities.

$Zn_{2-x}Mn_xSiO_4$ 형광체의 망간 K 흡수단 엑스선 흡수 분광 분석

최용규,임동성,김경현,손기선,박희동,Choi, Yong Gyu,Lim, Dong Sung,Kim, Kyong Hon,Sohn, Kee Sun,Park, Hee Dong 대한화학회 1999 대한화학회지 Vol.43 No.6

PDP(plasma display panel)의 녹색 광원으로 유망한 $Zn_{2-x}Mn_xSiO_4$ 헝광체를 1300$^{\circ}C$에서 고상반응법으로 제조한 후 900$^{\circ}C$에서 후속 열처리를 실시하면 녹색 형광의 강도가 현저히 증가한다. 열처리를 통한 형광 강도의 향상과 망간의 산화 상태 및 국부 구조 변화와의 관계를 파악하고자 망간 K 흡수단의 엑스선 흡수 스펙트럼을 분석하였다. $1s{\rightarrow}3d$ 전이에 해당하는 프리엣지(preedge) 봉우리와 XANES 스펙트럼을 분석한 결과, 망간은 열처리와 무관하게 +2가의 산화 상태를 유지하였으며 Zn 자리를 치환하는 것으로 밝혀졌다. 또한 EXAFS 스펙트럼의 분석을 통하여, Mn은 $MnO_4$ 사면체를 형성하고 Mn-O 쌍의 결합 길이와 디바이월러 인자(Debye-Waller factor)는 열처리 후 공히 감소함을 알 수 있었다. Green-emission intensity of a $Zn_{2-x}Mn_xSiO_4$ phosphor, which is a potential candidate as a green component in PDP device, significantly increases provided that the compound is additionally heat treated at 900$^{\circ}C$ after solid state reaction at 1300$^{\circ}C$. In order to verify origin of such an intensity enhancement after the additional heat treatment in association with the electronic and local structural change at around Mn ions, the Mn K-edge X-ray absorption spectra were recorded. From the analyses of the preedge peak corresponding to $1s{\rightarrow}3d$ bound state transition and XANES spectrum, it is known that most Mn ions are in +2 oxidation state and substitute Zn ion site regardless of the thermal treatment. In addition, EXAFS analyses revealed that Mn ions formed $MnO_4$ tetrahedra with the Mn-O bond length shortened by 0.01${\AA}$ and with reduced Debye-Waller factor in the thermally treated sample.

희토류 원소 첨가 비정질 찰코지나이드 : 형광 수명과 유리 구조 변화의 관계

최용규,Choi Yong Gyu 한국세라믹학회 2004 한국세라믹학회지 Vol.41 No.9

Lifetime of excited electronic states inside the 4f configuration of rare-earth elements embedded in chalcogenide glasses is very sensitive to medium-range structural changes of the host glasses. We have measured lifetimes of the 1.6$\mu\textrm{m}$ emission originating from Pr$\^$3+/ : ($^3$F$_3$, $^3$F$_4$)\longrightarrow$^3$H$_4$ transition in amorphous chalcogenide samples consisting of Ge, Sb, and Se elements. The measured lifetimes fumed out to have their maximum at the mean coordination number of -2.67, which arises accordingly from structural changes of the host glasses from 2 dimensional layers to 3 dimensional networks. This new finding supports that the so-called topological structure model together with chemically ordered network model is adequate to explain relationship between the emission properties of rare-earth elements and the medium-range structures of amorphous chalcogenide hosts with a large covalent bond nature. Thus, it is validated to predict site distribution and lifetime of rare-earth elements doped in chalcogenide glasses simply based on their mean coordination number.

중금속 산화물 유리내 희토류 원소의 Multiphonon Relaxation 현상

최용규,허종,Choi, Yong-Gyu,Heo, Jong 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.4

Er 첨가 황화물계 광섬유의 제조 및 분광학적 특성

최용규,임동성,김경헌,박세호,허종,Choi, Yong-Gyu,Lim, Dong-Sung,Kim, Kyong-Hon,Park, Se-Ho,Heo, Jong 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.8

An Er-doped sulfide fiber was drawn, and its spectroscopic properties were analyzed. Compositions of a 1000 ppmwt Er3+-doped core and an undoped clad were Ge30-Ga1-Asg-S61 and Ge30-As8-S62, in at.%, respectively. Refractive index of the core composition was approximately 0.01 high than that of the clad. In order to enhance the mechanical stability as well as to prevent infiltration of impurity ions such as OH-, an UV-curable polymer was used for the coating. The optical loss of a fiber formed directly from a polymer coated core rod without cladding was ∼15 dB/m at 1.06$\mu\textrm{m}$. In the case of a fiber with core/clad structure, the optical loss was so high that the stimulated emission of erbium fluorescence was not evident. It is believed that presence of inhomogeneous core/clad interface and crystalline aggregates precipitated in the clad region were responsible for the high optical loss. On the other hand, fluorescence characteristics of Er3+ embedded in the core region were more or loss deteriorate compared to fiber preform, which is attributed to the redistribution of the Er ions along with the partial crystallization of the core glass during the fiberization process.

PbO-$Bi_2O_3-Ga_2O_3$ 유리내 $Nd_{3+}$와 $OH_-$ 사이의 에너지 전달 현상

최용규,허종,Choi, Yong-Gyu,Heo, Jong 한국세라믹학회 1996 한국세라믹학회지 Vol.33 No.8

저주파 능동 반향음 저감 연구

최용규(Yong-Gyu Choi),천원종(Won-jong Chun),김재필(Jae-Pil Kim),서영수(Young-Soo Seo) 한국소음진동공학회 2016 한국소음진동공학회 학술대회논문집 Vol.2016 No.10

Er³+ 첨가 중금속 산화물 유리의 다중포논 완화와 주파수 상향 전이 현상

최용규(Yong Gyu Choi),김경헌(Kyong Hon Kim),허종(Jong Heo) 한국광학회 1998 한국광학회지 Vol.9 No.4

Er₂O₃를 첨가한 PbO-Bi₂O₃-Ga₂O₃ 삼성분계 중금속 산화물 유리로부터 발생하는 1.5㎛와 2.7㎛ 등의 형광에 대하여 복사 천이율, 형광 수명, 흡수 및 유도 방출 단면적 등을 조사하였다. 중금속 산화물 유리의 낮은 포논 에너지 (~500㎝-¹)로 인하여 기존 산화물 유리로부터 관찰할 수 없었던 형광들의 양자 효율이 크게 높아졌으며 방출 단면적도 증가하였다. 한편, 798㎚ 여기광의 상향 전이를 통한 녹색과 적색의 형광이 방출됨을 확인하였고, 각 에너지 준위의 형광 수명을 이용하여 다중포논 완화(multiphonon relaxation)를 정량적으로 규명하였다. Er³+: ⁴S_(3/2) → ⁴I_(15/2) 천이에 의한 녹색 형광은 기지 유리 (host glass)의 밴드 갭(band gap) 흡수에 의한 비복사 천이의 영향을 받으므로 이 형광의 양자 효율을 높이기 위해서는 유리를 불활성 기체 분위기에서 용융하거나 자외선쪽 투과단이 짧은 유리 망목 형성제 (glass-network former)가 첨가된 기지 조성을 선택하는 것이 바람직하다. Ternary heavy metal oxide glasses in the PbO-Bi₂O₃-Ga₂O₃ system doped with Er₂O₃ were prepared and their spectroscopic properties, such as radiative transition probability, calculated and measured radiative lifetimes and cross-sections of 1.5㎛ and 2.7㎛ emissions were analyzed. Enhanced quantum efficiencies of some electronic transitions were evident mainly because of the low vibrational phonon energy (~500㎝-¹) inherent in the host glasses. This seems to be the main reason for obtaining the 2.7㎛ luminescence which is normally quenched in the conventional oxide glasses. In addition, green and red fluorescence emissions were observed through the frequency upconversion processes of the 798㎚ excitation. Non-radiative transition due to the multiphonon relaxation is a dominant lifetime-shortening mechanism in the 4f-4f transitions in Er³+ ion except for the ⁴S_(3/2) → ⁴I_(15/2) transition where a non-radiative transfer to band-gap excitation of the host glasses is dominant. Melting of glasses under an inert gas atmosphere and (or) addition of the typical glass-network former into glasses is necessary in order to enhance the quantum efficiency of the transition.