• 반도체디스플레이기술학회지
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• 제22권1호
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• pp.83-87
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• 2023

Y₂SiO₅ Powder based on silicon and yttrium is well known as powder phosphors due to their excellent sustainability and efficiency. A new electroluminescence device was fabricated with Y₂SiO₅:Eu³⁺ powder phosphors though a simple screen printing method. The powder-dispersed electroluminescence device consisted of the Y₂SiO₅:Eu³⁺ powder-dispersed phosphor layer and BaTiO₃-dispersed dielectric layer. The annealing temperature of the phosphor for the best powder electroluminescence performance was optimized to high temperature in ambient atmosphere though a solid-state reaction. The Eu³⁺ concentration for the best device performance was also investigated and furthermore, the thermal dependence of the electroluminescence intensity was investigated at the operating voltage at 100℃, which is the Curie temperature of the BaTiO₃ layer. And the intensity was exponentially increased with voltage and increased linearly with frequency.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4642-4646
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• 2023

The Tb³⁺ or Eu³⁺-doped Lu₂Gd₁Ga₂Al₃O₁₂ phosphor were fabricated by funace at 1500 ℃ for 12 h using a solid state reaction. The XRD (X-ray diffraction_Panalytical X'Pert Pro) and FE-SEM (field emission scanning electron microscope) are measured to confirm the crystalline structure and surface morphology of the phosphor. The Tb³⁺-doped Lu₂Gd₁Ga₂Al₃O₁₂ phosphor emits the lights in 470~650 nm wavelength range due to transitions from ⁵D₄ to ⁷F_j. Therefore, it shows the green region in the CIE chromaticity diagram under both UV and X-rays excitations. The Eu³⁺-doped Lu₂Gd₁Ga₂Al₃O₁₂ phosphor emits the lights in 550~750 nm wavelength range because of ⁵D_i to ⁷F_j. The emission is confirmed to be in the red region using the CIE chromaticity diagram. The Tb³⁺ or Eu³⁺-doped Lu₂Gd₁Ga₂Al₃O₁₂ phosphor shows the characteristic f-f transition with a long decay time, which is about several milliseconds. They have the high efficiency of light emission for X-ray because of their high effective Z number (Z_eff = 58.5) and density. Therefore, they are very much promising phosphors for X-ray imaging application in medical fields.

• 한국세라믹학회지
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• 제47권2호
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• pp.122-126
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• 2010

In this article photoluminescence of the $Al_2O_3:xCr_2O_3$ solid solutions prepared by solid state reaction method are represented. The effect of $Cr_2O_3$-activator concentration and heat treatment time on the PL characteristics have been discussed in conjunction with microstructure of phosphor samples. The $Al_2O_3:xCr_2O_3$ phosphors show the highest PL intensity at x=0.003 mole when the samples are reacted at $1600^{\circ}C$ for 5 h. The PL emission and absorption spectra show the maximum peaks at 698 nm and at 398 nm respectively. The CIE color coordinate is (x=0.646, y=0.316) at 0.003 mole $Cr_2O_3$, which value is very close to the NTSC coordinate of red color. This characteristic feature of $Al_2O_3:xCr_2O_3$ has been applied for an additive to improve the color characteristic of other red phosphor $LiEuW_2O_8$ which has a relatively poor color purity with an emission peak centered at 615 nm and with a CIE coordinate (x=0.530, y=0.280). The $Al_2O_3:0.003Cr_2O_3$ phosphor has been mixed with the $LiEuW_2O_8$ phosphor powder and the PL characteristics and CIE color coordinates are characterized. The $Al_2O_3:xCr_2O_3$ phosphor was found effective for improving the CRI (color rendering index) of $LiEuW_2O_8$ phosphor.

• 한국결정성장학회지
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• 제22권5호
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• pp.233-240
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• 2012

백색 발광다이오드(white light-emitting diodes)를 이용한 광소자는 소비전력이 상대적으로 작고, 안정적이며, 수은과 같은 유해 중금속을 포함하지 않기 때문에, 에너지 절약 및 친환경 산업측면에서 유망한 산업으로 급속히 발전하고 있다. 국내의 경우 LED 조명의 효율, 신뢰성, 연색성을 향상시키는데 필수 소재인 형광체의 기술 확보에 대한 관심이 높아지고 있다. 이러한 관점에서 기존의 YAG, TAG, silicate 계열 산화물 형광체 뿐만 아니라 고온특성이 우수한 산/질화물계 형광체 개발에 대한 관심이 높아지고 있다. 특히 산/질화물계 형광체 조성에서 $M_2Si_5N_8$ : $Eu^{2+}$, $MAlSiN_3$ : $Eu^{2+}$ M-SiON(M = Ca, Sr, Ba), ${\alpha}/{\beta}$-SiAlON : $Eu^{2+}$과 같은 재료는 440~460 nm 영역에서의 넓은 여기파장과 우수한 발광효율로 청색 LED 칩을 이용한 백색 LED에 넓게 사용되고 있다. 이 논문에서는 이러한 산/질화물계 형광체 조성의 결정학적, 광학적 특성 및 응용에 대해서 정리하였다. 또한 최근에 주목받고 있는 양자점(quantum dots) 형광체를 응용한 white LEDs의 개발동향에 대해서도 알아보도록 한다.

• 한국진공학회지
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• 제22권2호
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• pp.79-85
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• 2013

희토류 이온 $Eu^{3+}$와 $Dy^{3+}$가 각각 도핑된 $CaMoO_4$ 광체 분말을 고상반응법으로 합성하였다. 모든 형광체 분말의 결정 구조는 활성제 이온의 종류와 농도비에 관계없이 주 회절 피크(112)를 갖는 정방 정계이었다. $Eu^{3+}$ 이온이 도핑된 형광체의 경우에, $Eu^{3+}$ 이온의 농도가 0.01~0.10 mol 영역에서 결정 입자의 크기는 전반적으로 증가하였고, 비교적 균일한 크기 분포를 가지면서 조약돌 형태를 나타내었으며, 흡광 스펙트럼은 311 nm를 정점으로 넓게 퍼져있는 전하 전달 밴드와 파장 영역 360~470nm에서 약한 피크를 갖는 다수의 흡수선이 관측되었으며, 주 발광 스펙트럼은 $Eu^{3+}$ 이온의 $^5D_0{\rightarrow}^7F_2$ 전이에 의한 618 nm에 피크를 갖는 강한 적색 발광이었다. $Dy^{3+}$ 이온이 도핑된 분말의 경우에, 흡광 스펙트럼은 303 nm에 피크를 갖는 전하 전달 밴드와 상대적으로 세기가 약한 다수의 $Dy^{3+}$ 이온의 전이 신호가 발생하였으며, 주 발광 스펙트럼은 $^4F_{9/2}{\rightarrow}^7H_{13/2}$ 전이에 의한 578 nm에 피크를 갖는 황색 발광 스펙트럼이 관측되었다.

• 한국세라믹학회지
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• 제44권3호
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• pp.147-151
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• 2007

An improvement for the efficiency of the $Sr_{2}SiO_{4}:Eu$ yellow phosphor under the $450{\sim}470\;nm$ excitation range have been achieved by adding the co-doping element ($Mg^{2+}\;and\;Ba^{2+}$) in the host. White LEDs were fabricated through an integration of an blue (InGaN) chip (${\lambda}_{cm}=450\;nm$) and a blend of two phosphors ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) in a single package. The InGaN-based two phosphor blends ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) LEDs showed three bands at 450 nm, 550 nm and 640 nm, respectively. The 450 nm emission band was due to a radiative recombination from an InGaN active layer. This 450 nm emission was used as an optical transition of the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor. As a consequence of a preparation of white LEDs using the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor yellow phosphor and CaS:Eu red phosphor, the highest luminescence efficiency was obtained at the 0.03 mol $Ba^{2+}$ concentration. At this time, the white LEDs showed the CCT (5300 K), CRI (89.9) and luminous efficacy (17.34 lm/W).

• 한국재료학회지
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• 제24권11호
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• pp.599-603
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• 2014

$NaLa_{1-x}(MoO_4)_2:Eu^{3+}/Yb^3$ phosphors with doping concentrations of $Eu^{3+}$ and $Yb^{3+}$ ($x= Eu^{3+}+Yb^{3+}$, $Eu^{3+}=0.05$, 0.1, 0.2 and $Yb^{3+}= 0.2$, 0.45) were successfully synthesized by the microwave-modified sol-gel method, and the upconversion and spectroscopic properties were investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of $2-5{\mu}m$. Under excitation at 980 nm, $NaLa_{0.5}(MoO_4)_2:Eu_{0.05}Yb_{0.45}$ particles exhibited a strong 525-nm emission band and a weak 550-nm emission band in the green region, and a very weak 665-nm emission band in the red region. The strong 525-nm emission in the green region corresponds to the $^7F_1{\rightarrow}^5D_1$ transition and the weak 550-nm emission in the green region corresponds to the $^7F_0{\rightarrow}^5D_2$ transition, while the very weak emission 665-nm band in the red region corresponds to the $^5D_0{\rightarrow}^7F_3$ transition. The Raman spectra of the doped particles indicated the domination of strong peaks at higher frequencies of 762, 890, 1358 and $1430cm^{-1}$ and weak peaks at lower frequencies of 323, 388 and $450cm^{-1}$ induced by the disorder of the $[MoO4]^{2-}$ groups with the incorporation of the $Eu^{3+}$ and $Yb^{3+}$ elements into the crystal lattice or by a new phase formation.

• 한국결정성장학회지
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• 제18권4호
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• pp.169-173
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• 2008

본 연구에서는 자외선 영역에서 우수한 발광강도를 가지는 적색 형광체를 얻기 위하여 microwave 급속 열처리법으로 합성하여 $Eu^{3+}$와 $Bi^{3+}$가 도핑된 $YVO_4$의 발광특성을 관찰하였다. Microwave 급속 열처리시 입자의 크기는 매우 미세하며, 응집이 매우 심하였으나 열처리 유지시간이 증가할수록 입자 크기는 증가하고 응집현상은 개선되는 경향을 나타내었다. $YVO_4$: $Eu^{3+}$, $Bi^{3+}$ 적색 형광체의 발광 peak는 $Eu^{3+}$ ion의 영향에 의해 594.9 nm와 602.3 nm에서 $^5D_0{\longrightarrow}^7F_1$ 전자 천이에 의한 약한 발광 peak와 616.7 nm와 620.0 nm에서 $^5D_0{\longrightarrow}^7F_2$ 전자 천이에 의한 강한 발광 peak이 관찰 되었다. Microwave 급속 열처리법을 형광체 합성시 장시간 열처리 시간이 필요하지 않으면서 균일한 activator의 확산으로 인하여 발광특성을 향상시키는 것을 확인 할 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4321-4326
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• 2011

A new series of heteroleptic cyclometalated iridium(III) complexes has been synthesized and characterized by absorption, emission and cyclic voltammetry studies: $(pqx)_2Ir(acac)$ (1), $(dmpqx)_2Ir(acac)$ (2) and $(dfpqx)_2Ir(acac)$ (3) where pqx=2-phenylquinoxalinate, dmpqx=2-(2,4-dimethoxyphenyl)quinoxalinate, dfpqx=2-(2,4-difluorophenyl) quinoxalinate and acac=acetylacetonate anion. The reaction of excess acetylacetone with ${\mu}$-chloride-bridged dimeric iridium complex, $[(C\^N)_2Ir({\mu}-Cl)]_2$, gives a complex 1 and an unusual hydridoiridium(III) complex, $(pqx)IrH(acac)_2$ (4). The complex 1, 2 and 3 show their emissions in an orangered region (${\lambda}_{PL,max}$ = 583-616 nm), and the emission maxima can be tuned by the change of substituent at phenyl ring of 2-phenylquinoxaline ligand. The phosphorescent line shape indicates that the emissions originate predominantly from $^3MLCT$ states with little admixture of ligand-based $^3({\pi}-{\pi}^*)$ excited states. The structures of complex 3 and 4 are additionally characterized by a single crystal X-ray diffraction method. The complex 3 shows a distorted octahedral geometry around iridium(III) metal ion. A strong trans influence of the phenyl ring is examined. In complex 4, there are two discrete molecules which are mirror images each other at the ratio of 1:1 in an unit cell. We propose that the phosphorescent complex 1, 2 and 3 are possible candidates for the phosphors in OLEDs applications.

• 한국재료학회지
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• 제29권2호
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• pp.116-120
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• 2019

We prepared $Y_3Al_5O_{12};Ce^{3+},Pr3^{+}$ transparent ceramic phosphor using a solid state reaction method. By XRD pattern analysis and SEM measurement, our phosphors reveal an Ia-3d(230) space group of cubic structure, and the transparent ceramic phosphor has a polycrystal state with some internal cracks and pores. In the Raman scattering measurement with an increasing temperature, lattice vibrations of the transparent ceramic phosphor decrease due to its more perfect crystal structure and symmetry. Thus, low phonon generation is possible at high temperature. Optical properties of the transparent ceramic phosphor have broader excitation spectra due to a large internal reflection. There is a wide emission band from the green to yellow region, and the red color emission between 610 nm and 640 nm is also observed. The red-yellow phosphor optical characteristics enable a high Color Rendering Index (CRI) in combination with blue emitting LED or LD. Due to its good thermal properties of low phonon generation at high temperature and a wide emission range for high CRI characteristics, the transparent ceramic phosphor is shown to be a good candidate for high power solid state white lighting.