• 한국재료학회지
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• 제21권11호
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• pp.604-610
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• 2011

The effect of $BaF_2$ flux in $Y_3Al_5O_{12}:Ce^{3+}$(YAG:Ce) formation was investigated. Phase transformation of $Y_3Al_5O_{12}$(YAG) was characterized by using XRD, SEM, and TEM-EDS, and it was revealed that the sequential formation of the $Y_4Al_2O_9$(YAM), $YAlO_3$(YAP) and $Y_3Al_5O_{12}$(YAG) in the temperature range of 1000-1500$^{\circ}C$. Single phase of YAG was revealed from 1300$^{\circ}C$. In order to find out the effect of $BaF_2$ flux, three modeling experiments between starting materials (1.5$Al_2O_3$-2.5$Y_2O_3$, $Y_2O_3$-$BaF_2$, and $Al_2O_3$-$BaF_2$) were done. These modeling experiments showed that the nucleation process occurs via the dissolution-precipitation mechanism, whereas the grain growth process is controlled via the liquid-phase diffusion route. YAG:Ce phosphor particles prepared using a proposed technique exhibit a spherical shape, high crystallinity, and an emission intensity. According to the experimental results conducted in this investigation, 5% of $BaF_2$ was the best concentration for physical, chemical and optical properties of $Y_3Al_5O_{12}:Ce^{3+}$(YAG:Ce) that is approximately 10-15% greater than that of commercial phosphor powder.

• 한국재료학회지
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• 제23권1호
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• pp.31-34
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• 2013

Trivalent cerium-ion-doped $Y_3(Al,\;Ga)_5O_{12}$ nanoparticle phosphor nanoparticles were synthesized using the reverse micelle process. The Ce doped $Y_3(Al,\;Ga)_5O_{12}$ particles were obtained from nitrate solutions dispersed in the nanosized aqueous domains of a micro emulsion consisting of cyclohexane as the oil phase and poly(oxyethylene) nonylphenyl ether (Igepal CO-520) as the non-ionic surfactant. The crystallinity, morphology, and thermal properties of the synthesized $Y_3(Al,\;Ga)_5O_{12}:Ce^{3+}$ powders were characterized by thermogravimetry-differential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscopy. The crystallinity, morphology, and chemical states of the ions were characterized; the photo-physical properties were studied by taking absorption, excitation, and emission spectra for various concentrations of cerium. The photo physical properties of the synthesized $Y_3(Al,\;Ga)_5O_{12}:Ce^{3+}$ powders were studied by taking the excitation and emission spectra for various concentrations of cerium. The average particle size of the synthesized YAG powders was below $1{\mu}m$. Excitation spectra of the $Y_3Al_5O_{12}$ and $Y_3Al_{3.97}Ga_{1.03}O_{12}$ samples were 485 nm and 475 nm, respectively. The emission spectra of the $Y_3Al_5O_{12}$ and $Y_3Al_{3.97}Ga_{1.03}O_{12}$ were around 560 nm and 545 nm, respectively. $Y_3(Al,\;Ga)_5O_{12}:Ce^{3+}$ is a red-emitting phosphor; it has a high efficiency for operation under near UV excitation, and may be a promising candidate for photonic applications.

• 대한환경공학회지
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• 제37권12호
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• pp.668-673
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• 2015

마이크로파 열분해 시스템을 이용하여 Ce 담지량이 다른 알루미나 촉매의 $CF_4$ 분해에 대한 연구를 실시하였다. 마이크로파 발열체로는 실리콘카바이드를 사용하였다. 각 촉매의 결정상은 XRD로 관찰하였으며 $CF_4$의 분해율은 GC-TCD를 사용하였다. $500^{\circ}C$ 반응온도에서 10 wt% Ce로 개질화한 알루미나가 개질화하지 않은 알루미나에 비해 $CF_4$ 분해율이 높았다. 반응속도상수 k값은 $Ce(20)/Al_2O_3=Ce(0)/Al_2O_3 순이었다. XRD 패턴은 $Ce(0)/Al_2O_3$에서는 반응 전후의 차이가 나타나지 않았으며 $Al_2O_3$의 결정구조만 관찰되었다. 반면에 Ce를 담지한 촉매에서는 산화알루미늄와 산화세륨의 혼합형으로 나타났다. 본 연구의 결과 Ce를 담지한 $Al_2O_3$촉매는 Ce를 담지하지 않은 촉매에 비해 동일한 분해율을 가지면서 반응온도를 $200^{\circ}C$ 정도를 낮출 수 있음을 보여주었다. 또한 cerium sulfate의 적정비율은 5~10 wt%임을 보여주었다.

• The Korean Journal of Ceramics
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• 제4권4호
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• pp.297-303
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• 1998

The effect of aliovalent dopants, $ Nb_2O_5$ and MnO, on the phase stability of 12 mol% ceria partially-stabilized zirconia (Ce-TZP) polycrystals was studied. Both dopants (MnO and $ Nb_2O_5$) significantly increased the stability of the tetragonal zirconia phase (Mb temperature lower than liquid nitrogen temperature). The enhancement of the stability of the tetragonal phase in Ce-TZP doped with 1 mol% of Mno(Ce-TZP/MnO) andCe-TZP doped with 1 mol% of $ Nb_2O_5$(Ce-TZP/$ Nb_2O_5$) were explained by the significant reduction of the driving force, -${\Delta}$Gchem, for the tetragonal-to-mono-clinic phase transformation caused by the addition of MnO and $ Nb_2O_5$. The enhanced stability of the tetragonal phase in the Ce-TZP and Al2O3 composite (Ce-TZP/$Al_2O_3$) is believed to be caused by smaller grain size, moderate reduction in the chemical driving force and increase in the strain energy barrier to the transformation. Mechanical properties of the Ce-TZP and the Ce-TZP/$Al_2O_3$ with (i) the same grain size and (ii) the same Mb temperature were examined by measuring stress-strain behavior in 3 point bending. The Ce-TZP/$Al_2O_3$ composite doped with 1.3w% MnO (Ce-TZP/$Al_2O_3$/MnO), which had the same grain size as the Ce-TZP and De-TZP/$Al_2O_3$ showed more transformation plasticity than either the Ce-TZP or the Ce-TZP/$Al_2O_3$ composite. The Ce-TZP wihch had the same Mb temperature as that of the Ce-TZP/$Al_2O_3$/MnO did not show any transformation plasticity.

• 한국세라믹학회지
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• 제53권4호
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• pp.463-467
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• 2016

$Si^{4+}-N^{3-}$ was incorporated into $Ce^{3+}-doped$ lutetium aluminum garnet ($Lu_{2.965}Ce_{0.035}Al_5O_{12}$, $LuAG:Ce^{3+}$) lattices, resulting in the formation of $Lu_{2.965}Ce_{0.035}Al_{5-x}Si_xO_{12-x}N_x$ [(Lu,Ce)AG:xSN]. For x = 0-0.25, the synthesized powders consisted of the LuAG single phase, and the lattice constant decreased owing to the smaller $Si^{4+}$ ions. However, for x > 0.25, a small amount of unknown impurity phases was observed, and the lattice constant increased. Under 450 nm excitation, the PL spectrum of $LuAG:Ce^{3+}$ exhibited the green band, peaking at 505 nm. The incorporation of $Si^{4+}-N^{3-}$ into the $Al^{3+}-O^{2-}$ sites of $LuAG:Ce^{3+}$ led to a red-shift of the emission peak wavelength from 505 to 570 nm with increasing x. Corresponding CIE chromaticity coordinates varied from the green to yellow regions. These behaviors were discussed based on the modification of the $5d^1$ split levels and crystal field surroundings of $Ce^{3+}$, which arose from the Ce-(O,N)8 bonds.

• 한국재료학회지
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• 제10권5호
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• pp.321-327
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• 2000

다공성 알루미나 소결체내부로 3Y-TZP 및 12Ce-TZP 전구체를 각각 액상침투시킴으로써 2종류의 $Al_2O_3/TZP$복합체를 제조하였다. 소량의 (~11.0 wt%) TZP의 첨가는 Al2O3소결체 ($1600^{\circ}C$, 2시간)의 강도 (19~59%)와 파괴인성(14~157%)을 증가시켰다. 3Y-TZP의 첨가는 복합체의 강도의 향상에 12Ce-TZP의 첨가는 인성의 향상에 보다 효과적이었다. 침투도니 TZP는 복합체의 내부보다 표면에 집중되었으며, 그 결과 이곳에서의 입성장에 빨랐고 $Al_2O_3$의입성장 억제효과도 상대적으로 뛰어났다. 입계 및 입내균열전파가 일어났으나 $Al_2O_3/12Ce-TZP$의 경우가 $Al_2O_3/3Y-TZP$에 비하여 입계파괴가 우세하였다

• 반도체디스플레이기술학회지
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• 제18권4호
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• pp.51-56
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• 2019

LuAG:Ce(Lu₃Al₅O₁₂:Ce³⁺) nano phosphor were synthesized by applying the coprecipitation method. It is used to increase the color rendering of phosphor ceramic plate for high power LEDs and laser lighting. Internal quantum efficiency and absorption of LuAG:Ce nano phosphor are 51.5 % and 64.4 %, respectively, which is higher than the previously studied nano phosphors. The maximum absorption wavelength of this phosphor is 450 nm blue light, and the emission wavelength is 510 nm. The emission wavelength shifted to longer wavelength when the concentration of Ce increased in the heat treatment of the reducing atmosphere. Thermal quenching of LuAG nano phosphor was 70 % at 200 ℃, it was explained by their significant quenching of all raman scattering modes, implying the restriction of electron-phonon couplings caused by their defects.

• 한국결정성장학회지
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• 제25권3호
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• pp.121-126
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• 2015

A novel $Ce^{3+}$ doped $Lu_3MgAl_3SiO_{12}$ phosphor ($Lu_{2.94}Ce_{0.06}MgAl_3SiO_{12}$) was successfully synthesized by a conventional solid-state reaction at $1450^{\circ}C$ for 5 h. The crystal structure of the synthesized phosphor powder was characterized by X-ray diffraction and Rietveld refinement. The prepared phosphor powder showed a broad peak at 550 nm, and the temperature dependence on photoluminescence properties of the prepared $Lu_{2.94}Ce_{0.06}MgAl_3SiO_{12}$ phosphor was investigated from 300 to 525 K. The activation energy for thermal quenching was determined by Arrhenius fitting. The experimental results clearly indicate that prepared $Lu_{2.94}Ce_{0.06}MgAl_3SiO_{12}$ phosphor has great potential for a down-conversion yellow phosphor in white light-emitting diodes.

• Bulletin of the Korean Chemical Society
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• 제23권10호
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• pp.1435-1454
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• 2002

Bright yellow ${(Y_{1-x}Gd_x)}_{3-z}{(Al_{1-y}Ga_y)}_5O_{12}:Ce_z$ phosphors were synthesized. White LED was obtained by the combination of non-absorbed blue emission from a blue L ED itself and yellow emission from ${(Y_{1-x}Gd_x)}_{3-z}{(Al_{1-y}Ga_y)}_5O_{12}:Ce_z$ phosphors. The crystal structures and optical properties of ${(Y_{1-x}Gd_x)}_{3-z}{(Al_{1-y}Ga_y)}_5O_{12}:Ce_z$ phosphors were investigated.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권2호
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• pp.1593-1596
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• 2007

Various yellow-emitting $Y_3Al_5O_{12}:Ce^{3+}$ (YAG:Ce) nanocrystalline phosphors, where some $Al^{3+}$ sites are substituted with $Ga^{3+}$ or some Y sites with Gd3+, have been synthesized. The rare earth ions such as $Pr^{3+}$ and $Tb^{3+}$ were also co-doped into YAG:Ce system, leading to the tunability of CIE coordinates of emission.