• Title/Summary/Keyword: Red-emitting phosphor

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Efficient Red-Color Emission of InGaN/GaN Double Hetero-Structure Formed on Nano-Pyramid Structure

  • Go, Yeong-Ho;Kim, Je-Hyeong;Gong, Su-Hyeon;Kim, Ju-Seong;Kim, Taek;Jo, Yong-Hun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.174-175
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    • 2012
  • (In, Ga) N-based III-nitride semiconductor materials have been viewed as the most promising materials for the applications of blue and green light emitting devices such as light-emitting diodes (LEDs) and laser diodes. Although the InGaN alloy can have wide range of visible wavelength by changing the In composition, it is very hard to grow high quality epilayers of In-rich InGaN because of the thermal instability as well as the large lattice and thermal mismatches. In order to avoid phase separation of InGaN, various kinds of structures of InGaN have been studied. If high-quality In-rich InGaN/GaN multiple quantum well (MQW) structures are available, it is expected to achieve highly efficient phosphor-free white LEDs. In this study, we proposed a novel InGaN double hetero-structure grown on GaN nano-pyramids to generate broad-band red-color emission with high quantum efficiency. In this work, we systematically studied the optical properties of the InGaN pyramid structures. The nano-sized hexagonal pyramid structures were grown on the n-type GaN template by metalorganic chemical vapor deposition. SiNx mask was formed on the n-type GaN template with uniformly patterned circle pattern by laser holography. GaN pyramid structures were selectively grown on the opening area of mask by lateral over-growth followed by growth of InGaN/GaN double hetero-structure. The bird's eye-view scanning electron microscope (SEM) image shows that uniform hexagonal pyramid structures are well arranged. We showed that the pyramid structures have high crystal quality and the thickness of InGaN is varied along the height of pyramids via transmission electron microscope. Because the InGaN/GaN double hetero-structure was grown on the nano-pyramid GaN and on the planar GaN, simultaneously, we investigated the comparative study of the optical properties. Photoluminescence (PL) spectra of nano-pyramid sample and planar sample measured at 10 K. Although the growth condition were exactly the same for two samples, the nano-pyramid sample have much lower energy emission centered at 615 nm, compared to 438 nm for planar sample. Moreover, nano-pyramid sample shows broad-band spectrum, which is originate from structural properties of nano-pyramid structure. To study thermal activation energy and potential fluctuation, we measured PL with changing temperature from 10 K to 300 K. We also measured PL with changing the excitation power from 48 ${\mu}W$ to 48 mW. We can discriminate the origin of the broad-band spectra from the defect-related yellow luminescence of GaN by carrying out PL excitation experiments. The nano-pyramid structure provided highly efficient broad-band red-color emission for the future applications of phosphor-free white LEDs.

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Synthesis and Photoluminescence Properties of Y1-x(P1-y-zNbyVz)O4:Eux Phosphors by Modified Combinatorial Chemistry Method (조합화학 기법을 이용한 Y1-x(P1-y-zNbyVz)O4:Eux 형광체의 합성 및 빛 발광 특성)

  • Zeon, Il-Woon;Sohn, Kee-Sun;Park, Hee-Dong
    • Journal of the Korean Chemical Society
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    • v.46 no.1
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    • pp.69-75
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    • 2002
  • The $Y_{1-x}(P_{1-y-z}Nb_yV_z)O_4:Eu_x$ blue and red emitting phosphors were prepared by the combinatorial chemistry method. The combinatorial library was designed to investigate the luminescence of the $Y_{1-x}(P_{1-y-z}Nb_yV_z)O_4:Eu_x$ phosphors under 254 nm and 147 nm excitations. In addition, the crystallinity and morphology of phosphors were checked by XRD and SEM. Based on the results from the combinatorial screenings, luminescent properties of phosphors are strongly dependent on the concentration of doping metal ions. It was found that a new phosphor $Y_{0.88}(P_{0.92}Nb_{0.05}V_{0.03})O_4:Eu_{0.12}$ shows excellent luminescent efficiency comparing to the $Y_{0.88}PO_4:Eu_{0.12}$ red phosphor.

Synthesis and Properties of SrMoO4 Phosphors Doped with Various Rare Earth Ions for Anti-Counterfeiting Applications (위조 방지 분야에 응용 가능한 다양한 희토류 이온이 도핑된 SrMoO4 형광체의 제조 및 특성)

  • Moon, Tae-Ok;Jung, Jae-Yong;Cho, Shinho
    • Korean Journal of Materials Research
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    • v.30 no.8
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    • pp.406-412
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    • 2020
  • SrMoO4:RE3+ (RE=Dy, Sm, Tb, Eu, Dy/Sm) phosphors are prepared by co-precipitation method. The effects of the type and the molar ratio of activator ions on the structural, morphological, and optical properties of the phosphor particles are investigated. X-ray diffraction data reveal that all the phosphors have a tetragonal system with a main (112) diffraction peak. The emission spectra of the SrMoO4 phosphors doped with several activator ions indicate different multicolor emissions: strong yellow-emitting light at 573 nm for Dy3+, red light at 643 nm for Sm3+, green light at 545 nm for Tb3+, and reddish orange light at 614 nm for Eu3+ activator ions. The Dy3+ singly-doped SrMoO4 phosphor shows two dominant emission peaks at 479 and 573 nm corresponding to the 4F9/26H15/2 magnetic dipole transition and 4F9/26H13/2 electric dipole transition, respectively. For Dy3+ and Sm3+ doubly-doped SrMoO4 phosphors, two kinds of emission peaks are observed. The two emission peaks at 479 and 573 nm are attributed to 4F9/26H15/2 and 4F9/26H13/2 transitions of Dy3+ and two emission bands centered at 599 and 643 nm are ascribed to 4G5/26H7/2 and 4G5/26H9/2 transitions of Sm3+. As the concentration of Sm3+ increases from 1 to 5 mol%, the intensities of the emission bands of Dy3+ gradually decrease; those of Sm3+ slowly increase and reach maxima at 5 mol% of Sm3+ ions, and then rapidly decrease with increasing molar ratio of Sm3+ ions due to the concentration quenching effect. Fluorescent security inks based on as-prepared phosphors are synthesized and designed to demonstrate an anti-counterfeiting application.

Improving the Color Gamut of a Liquid-crystal Display by Using a Bandpass Filter

  • Sun, Yan;Zhang, Chi;Yang, Yanling;Ma, Hongmei;Sun, Yubao
    • Current Optics and Photonics
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    • v.3 no.6
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    • pp.590-596
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    • 2019
  • To improve the color gamut of a liquid-crystal display (LCD), we propose a bandpass filter that is added to the backlight unit to optimize the backlight spectrum. The bandpass filter can only transmit red, green and blue light in the visible range, while reflecting the unwanted light. We study the optical properties of the bandpass filter using the transfer-matrix method, and the effect of the bandpass filter on the color gamuts of LCDs is also investigated. When a bandpass filter based on a 5-layer configuration comprising low and high refractive indices ((HL)2H) is used in phosphor-converted white-light-emitting diode (pc-WLED), K2SiF6:Mn4+ (KSF-LED), and quantum-dot (QD) backlights, the color gamuts of the LCDs improve from 72% to 95.3% of NTSC, from 92% to 106.7% of NTSC, and from 104.3% to 112.2% of NTSC respectively. When the incident angle of light increases to 30°, the color gamuts of LCDs with pc-WLED and KSF-LED backlights decrease by 2.9% and 1% respectively. For the QD backlight, the color gamut almost does not change. When the (HL)2H structure is coated on the diffusion film, the color gamut can be improved to 92.6% of NTSC (pc-WLED), 105.6% of NTSC (KSF-LED), and 111.9% of NTSC (QD). The diffusion film has no obvious effect on the color gamut. The results have an important potential application in wide-color-gamut LCDs.

Optical Properties of CaYAlO4:Tb3+/Eu3+/Ce3+ Phosphors (CaYAlO4:Tb3+/Eu3+/Ce3+형광체의 광학적 특성 분석)

  • Kang, Taewook;Ryu, Jongho;Kim, Jongsu;Kim, Gwang Chul
    • Journal of the Semiconductor & Display Technology
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    • v.16 no.4
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    • pp.86-90
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    • 2017
  • $Tb^{3+}$ or $Eu^{3+}$ or $Ce^{3+}$-doped $CaYAlO_4$ phosphor were synthesized by solid-state method. $CaYAlO_4:Tb^{3+}$ is shown that the $Tb^{3+}$-doping concentration has a significant effect on the $^5D_4/^5D_3{\rightarrow}7F_J$ (J=6,...,0) emission intensity of $Tb^{3+}$. The $CaYAlO_4:Tb^{3+}$ phosphors show tunable photoluminescence from blue to yellow with the change of doping concentration of $Tb^{3+}$ ions. The $CaYAlO_4:Eu^{3+}$ phosphors exhibit a red-orange emission of $Eu^{3+}$ corresponding to $^5D_0$, $_{1,2}{\rightarrow}^7F_J$ (J=4,...,0) transitions. The $CaYAlO_4:Ce^{3+}$ phosphors show a blue emission due to $Ce^{3+}$ ions transitions from the 5d excited state to the $^2F_{5/2}$ and $^2F_{7/2}$ ground states. The decay time of $CaYAlO_4:Tb^{3+}$ phosphors decrease from 1.33 ms to 0.97 ms as $Tb^{3+}$ concentration increases from 0.1 mol% to 7 mol%. The decay time of $CaYAlO_4:Eu^{3+}$ phosphors increase from 0.94 ms to 1.17 ms as $Eu^{3+}$ concentration increases from 1 mol% to 9 mol%.

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Structural and Luminescent Properties of Gd2WO6:RE3+ (RE = Dy, Sm, Dy/Sm) Phosphors for White Light Emitting Devices (백색광 소자 응용을 위한 Gd2WO6:RE3+ (RE = Dy, Sm, Dy/Sm) 형광체의 구조 및 발광 특성)

  • Park, Giwon;Jung, Jaeyong;Cho, Shinho
    • Journal of the Korean institute of surface engineering
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    • v.53 no.4
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    • pp.131-137
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    • 2020
  • A series of Dy3+, Sm3+, and Dy3+/Sm3+ doped Gd2WO6 phosphors were synthesized by the conventional solid-state reaction. The X-ray diffraction patterns revealed that all of the diffraction peaks could be attributed to the monoclinic Gd2WO6 crystal structure, irrespective of the type and the concentration of activator ions. The photoluminescence (PL) excitation spectra of Dy3+-doped Gd2WO6 phosphors contained an intense charge transfer band centered at 302 nm in the range of 240-340 nm and two weak peaks at 351 and 386 nm. Under an excitation wavelength of 302 nm, the PL emission spectra consisted of two strong blue and yellow bands centered at 482 nm and 577 nm. The PL emission spectra of the Sm3+-doped Gd2WO6 phosphors had a series of three peaks centered at 568 nm, 613 nm, and 649 nm, corresponding to the 6G5/26H5/2, 6G5/26H9/2, and 6G5/26H11/2 transitions of Sm3+, respectively. The PL emission spectra of the Dy3+- and Sm3+-codoped Gd2WO6 phosphors showed the blue and yellow emission lines originating from the 4F9/26H15/2 and 4F9/24H13/2 transitions of Dy3+ and reddish-orange and red emission bands due to the 4G5/26H7/2 and 4G5/26H9/2 transitions of Sm3+. As the concentration of Sm3+ increased from 1 to 15 mol%, the intensities of two PL spectra emitted by the Dy3+ ions gradually decreased, while those of the three emission bands due to the Sm3+ ions slowly increased, thus producing the color change from white to orange. The CIE color coordinates of Gd2WO6:5 mol% Dy3+, 1 mol% Sm3+ phosphors were (0.406, 0.407), which was located in the warm white light region.