• 한국광학회지
• /
• 제24권3호
• /
• pp.135-142
• /
• 2013

본 논문에서는 YAG:Ce와 $(Sr,Ba)_2SiO4:Eu$ 등 두 종류의 형광체를 사용하여 백색 LED를 제작하고 온도변화에 따라 각각의 백색 LED의 발광 특성이 어떻게 변하는지 조사하였다. 상온에서 $80^{\circ}C$ 사이의 구간에서 측정된 두 백색 LED의 발광 스펙트럼을 분석하기 위해 asymmetric double sigmoidal 함수를 활용하였다. 이 함수를 백색 LED의 청색 발광 및 황색 발광 피크에 적용해서 각 피크의 중심파장과 진폭, 반치폭 및 비대칭성을 온도의 함수로 구하였다. 그 결과 온도가 증가할수록 청색 피크의 중심파장이 장파장 쪽으로 천이되고 황색피크의 중심파장이 단파장 쪽으로 천이되며 비대칭성 또한 증가한다는 것을 확인할 수 있었다. 이러한 결과는 두 백색 LED의 색도변화에 반영되었는데, 실리케이트계 형광체 기반 LED의 색도 변화가 더 큼을 알 수 있었다. 발광효율 역시 온도가 증가할수록 크게 떨어지는 것을 볼 수 있었는데 YAG 형광체 기반 LED의 발광효율 저하 폭이 더 적음을 확인하였다. 이상의 결과는 YAG 형광체 기반 백색 LED가 실리케이트계 형광체 기반 LED에 비해 색도안정성, 발광효율, 연색지수 측면에서 더 뛰어나다는 것을 의미한다.

• Korean Chemical Engineering Research
• /
• 제44권6호
• /
• pp.609-613
• /
• 2006

분무열분해법에 의해 장파장 UV 여기원 하에서 높은 발광세기를 가지는 $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ 형광체를 제조하였다. 분무열분해공정 의해 제조된 $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ 형광체의 발광특성, 분말 형태 및 결정성에 대해 조사하였다. 분무열분해 공정에 의해 제조된 $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ 형광체는 모체를 구성하는 바륨과 스트론튬의 비에 따라 청녹색에서 황색에 이르기까지 다양한 파장대의 색을 구현할 수 있었다. x = 0인 $Ba_2SiO_4:Eu^{2+}$ 형광체의 경우 발광 중심파장이 500 nm였으며, x = 2인 $Sr_2SiO_4:Eu^{2+}$ 형광체의 경우 발광중심 파장이 554 nm였다. 분무열분해 공정에 의해 제조된 $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ 형광체는 구형의 형상을 띄지만 중공성의 입자 특성을 가졌다. 반면에 후열처리 과정을 거친 $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ 형광체는 큰 입자 크기와 불규칙한 형태를 가졌다. $Ba_{1.488}Sr_{0.5}SiO_4:Eu_{0.012}{^{2+}}$ 형광체가 환원분위기 하에서 후열처리 온도 $1,200^{\circ}C$에서 3시간 동안 후열처리 과정을 거쳤을 때 최적의 발광 세기를 가졌다.

• 한국재료학회지
• /
• 제27권6호
• /
• pp.339-344
• /
• 2017

A series of $CaNb_2O_6:Dy^{3+}$, $CaNb_2O_6$:$Eu^{3+}$ and $CaNb_2O_6:Dy^{3+}$, $Eu^{3+}$ phosphors were prepared by solid-state reaction process. The effects of activator ions on the structural, morphological and optical properties of the phosphor particles were investigated. XRD patterns showed that all the phosphors had an orthorhombic system with a main (131) diffraction peak. For the $Dy^{3+}$-doped $CaNb_2O_6$ phosphor powders, the excitation spectra consisted of one broad band centered at 267 nm in the range of 210-310 nm and three weak peaks; the main emission band showed an intense yellow band at 575 nm that corresponded to the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transition of $Dy^{3+}$ ions. For the $Eu^{3+}$-doped $CaNb_2O_6$ phosphor, the emission spectra under ultraviolet excitation at 263 nm exhibited one strong reddish-orange band centered at 612 nm and four weak bands at 536, 593, 650, and 705 nm. For the $Dy^{3+}$ and $Eu^{3+}$-codoped $CaNb_2O_6$ phosphor powders, blue and yellow emission bands due to the $^4F_{9/2}{\rightarrow}^6H_{15/2}$ and $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transitions of $Dy^{3+}$ ions and a main reddish-orange emission line at 612 nm resulting from the $^5D_0{\rightarrow}^7F_2$ transition of $Eu^{3+}$ ions were observed. As the concentration of $Eu^{3+}$ ions increased from 1 mol% to 10 mol%, the intensities of the emissions due to $Dy^{3+}$ ions rapidly decreased, while those of the emission bands originating from the $Eu^{3+}$ ions gradually increased, reached maxima at 10 mol%, and then slightly decreased at 15 mol% of $Eu^{3+}$. These results indicate that white light emission can be achieved by modulating the concentrations of the $Eu^{3+}$ ions incorporated into the $Dy^{3+}$-doped $CaNb_2O_6$ host lattice.

• 한국재료학회지
• /
• 제26권3호
• /
• pp.143-148
• /
• 2016

$CaAl_2O_4:RE^{3+}$(RE = Tb or Dy) phosphor powders were synthesized with different contents of activator ions $Tb^{3+}$ and $Dy^{3+}$ by using the solid-state reaction method. The effects of the content of activator ions on the crystal structure, morphology, and emission and excitation properties of the resulting phosphor particles were investigated. XRD patterns showed that all the synthesized phosphors had a monoclinic system with a main (220) diffraction peak, irrespective of the content and type of $Tb^{3+}$ and $Dy^{3+}$ ions. For the $Tb^{3+}$-doped $CaAl_2O_4$ phosphor powders, the excitation spectra consisted of one broad band centered at 271 nm in the range of 220-320 nm and several weak peaks; the main emission band showed a strong green band at 552 nm that originated from the $^5D_4{\rightarrow}^7F_5$ transition of $Tb^{3+}$ ions. For the $Dy^{3+}$-doped $CaAl_2O_4$ phosphor, the emission spectra under ultraviolet excitation at 298 nm exhibited one strong yellow band centered at 581 nm and two weak bands at 488 and 672 nm. Concentration-dependent quenching was observed at 0.05 mol of $Tb^{3+}$ and $Dy^{3+}$ contents in the $CaAl_2O_4$ host lattice.

• 반도체디스플레이기술학회지
• /
• 제5권3호
• /
• pp.1-4
• /
• 2006

White-light-emitting ZnS:Mn, Cu, Cl phosphors with spherical shape and the size of $20\;{\mu}m$ are successfully synthesized. They have the double phases of cubic and hexagonal structures. They are applied to electroluminescent (EL) devices by silk screen method with the following structure: $electrode/BaTiO_3$ insulator layer ($50{\sim}60\;{\mu}m$)/ ZnS:Mn, Cu, Cl phosphor layer ($30{\sim}50\;{\mu}m$)/ITO glass. The EL devices are driven with the voltage of 100 V and the frequency of 400 Hz. The EL devices show the three emission peaks. The blue and green emission bands are originated from $CICu^{2+}$ transition and $ClCu^+$ transition, respectively. The yellow emission band results from $^4T^6A$ transition of $Mn^{2+}$ ion. As an increase of Cu concentrations, the blue and green emission intensities decrease whereas the yellow emission intensity increases; the quality becomes warm white. It is due to the energy transfer from the blue and green bands to the yellow band.

• 한국표면공학회지
• /
• 제48권3호
• /
• pp.82-86
• /
• 2015

$Dy^{3+}$- and $Eu^{3+}$-codoped $CaMoO_4$ Phosphors were synthesized by using the solid-state reaction method. The crystal structure, morphology, and optical properties of the resulting phosphor particles were investigated by using the X-ray diffraction, field-emission scanning electron microscopy, and photoluminescence spectroscopy. XRD patterns exhibited that all the synthesized phosphors showed a tetragonal system with a main (112) diffraction peak, irrespective of the content of $Eu^{3+}$ ions. As the content of $Eu^{3+}$ ions increased, the grains showed a tendency to agglomerate. The excitation spectra of the synthesized powders were composed of one strong broad band centered at 305 nm in the range of 220 - 350 nm and several weak peaks in the range of 350 - 500 nm resulting from the 4f transitions of activator ions. Upon ultraviolet excitation at 305 nm, the yellow emission line due to the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transition of $Dy^{3+}$ ions and the main red emission spectrum resulting from the $^5D_0{\rightarrow}^7F_2$ transition of $Eu^{3+}$ ions were observed. With the increase of the content of $Eu^{3+}$, the intensity of the yellow emission band gradually decreased while that of the red emission increased. These results indicated that the emission intensities of yellow and red emissions could be modulated by changing the content of the $Dy^{3+}$ and $Eu^{3+}$ ions incorporated into the host crystal.

• 한국세라믹학회지
• /
• 제49권1호
• /
• pp.105-110
• /
• 2012

In this paper, a yellow phosphor $Sr_3SiO_5:Eu^{2+}$ that emits efficiently at the 450 nm excitation for warm white LED is studied. In addition, the effects of various flux $BaF_2$, $NH_4Cl$ on the emission spectra were investigated. The samples were synthesized through conventional solid state reaction under reducing atmosphere of 95% $N_2$-5% $H_2$ mixture at the high temperature. All phosphors showed a excitation band from 450 nm and broad band emission peaking at region of 580 nm. The optimal concentration of $BaF_2$ flux is 3 wt% for $Sr_3SiO_5$ with doping 0.05mol Eu phosphors fired in a reductive atmosphere. The phosphor showed highest emission peaking at 582 nm.

• Bulletin of the Korean Chemical Society
• /
• 제35권10호
• /
• pp.2917-2921
• /
• 2014

Cerium-activated yttrium aluminate ($Y_3Al_5O_{12}:Ce^{3+}$) exhibiting a garnet structure has been widely utilized in the production of light emitting diodes (LEDs) as a yellow emitting phosphor. The commercialized yttrium aluminum garnet (YAG) phosphor is typically synthesized by a solid-state reaction, which produces irregular shape particles with a size of several tens of micrometers by using the top-down method. To control the shape and size of particles, which had been the primary disadvantage of top-down synthetic methods, we synthesized YAG:Ce nanoparticles with a diameter of 500 nm using a coprecipitation method under the atmospheric pressure without the use of template or special equipment. The precursor particles were formed by refluxing an aqueous solution of the nitrate salts of Y, Al, and Ce, urea, and polyvinylpyrrolidone (55 K) at $100^{\circ}C$ for 12 h. YAG:Ce nanoparticles were formed by the calcination of precursor particles at $1100^{\circ}C$ for 10 h under atmospheric conditions. The phase identification, microstructure, and photoluminescent properties of the products were evaluated by X-ray powder diffraction, scanning electron microscopy, absorption spectrum and photoluminescence analyses.

• 한국재료학회지
• /
• 제15권8호
• /
• pp.548-553
• /
• 2005

Trivalent cerium$(Ce^{3+})$ activated YAG (yttrium aluminum garnet, $Y_3Al_5O_{12})$) thin films phosphor were deposited on quartz glass substrates by rf magnetron sputtering. The effects of sputtering parameters, annealing atmosphere, and substrates on growing behaviors and luminescent properties were investigated. The sputtering parameters were $O_2/(Ar+O_2)$ gas ratio, rf power, and deposition time. XRD (X-ray diffractometery) spectra exhibited that as-deposited films were amorphous, while they were transformed to the crystalline phases by post-annealing. The crystallinity and the atomic ratio strongly depended on the sputtering gas ratio $O_2/(Ar+O_2)$. High quality YAG:Ce thin films could be obtained at the gas ratio of $50\%$ oxygen. After annealing process, PL (Photoluminescence) spectra excited at 450nm showed a yellow single band at 550nm. The films deposited at the sputtering gas ratio of 50% oxygen exhibited the highest PL intensity.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
• /
• pp.56-59
• /
• 2009

In the nineties the invention of the InGaN blue LED has innovated illumination technology. Currently LCD backlighting and more and more general lighting applications are based on white LEDs comprising of inorganic phosphors and blue emitting InGaN chip. Well established phosphor materials are ortho silicates and garnets like yellow emitting YAG:Ce. In our paper we demonstrate that garnet materials also allow for green light emission for both, general lighting and backlighting LED applications.