High Efficiency Wavelength Converting Nanophosphors: A Study on Size Control, Optical Properties and Applications
- 주제(키워드) Nanostructured materials , Wavelength conversion , Red phosphors , Greenhouse effect , High quantum efficiency
- 발행기관 Department of Chemistry, Sogang University, Seoul
- 지도교수 Professor Young Soo Kang
- 발행년도 2013
- 학위수여년월 2013. 2
- 학위명 박사
- 학과 및 전공 일반대학원 화학과
- 실제URI http://www.dcollection.net/handler/sogang/000000049428
- 본문언어 영어
- 저작권 서강대학교 논문은 저작권 보호를 받습니다.
초록/요약
Chapter 1: Size controlled synthesis of metal oxide nanoparticles by wet chemical methods: Synthesis of phosphor material has been carried out by two kinds of methods such as conventional solid-state reactions and by wet chemical method. The synthesis of phosphor material strongly affects its optical properties and its technological use. Most of the properties of these phosphor materials are dependent on its size. We will investigate the details of each method to understand why chemical methods are more preferred over conventional solid-state methods for high end application of these oxide materials.
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Chapter 2: Effect of different surfactant on the size control and optical properties of Y2O3:Eu3+ nanoparticles prepared by co-precipitation method: Nanoparticles of europium-doped yttrium oxide (Y2O3:Eu3+) were synthesized by co-precipitation method with use of different surfactants like butanol, hexanol, and oleic acid. The as-prepared Y2O3:Eu3+ samples were annealed at 800 °C and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and UV-visible and photoluminescence (PL) spectroscopy techniques. The nanoparticle shows cubic phase structure. Surfactant helps to inhibit or control the particle growth and avoids agglomeration of nanoparticles effectively by reducing the oxygen bridge bonds between the particles. The most intense red emission peak occurs at 614 nm at an excitation wavelength of λ = 200 nm. Nanoparticles of Y2O3:Eu3+ with a particle size of 30 nm synthesized by using oleic acid with NaCl show a 73% rise in PL intensity of the 614 nm peak.
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Chapter 4: Y2O3:Eu3+ nanophosphors with above 80% down conversion efficiency: Obtaining nanophosphors of controlled size and shape with high quantum efficiency is the current challenge for optical display and bio-imaging industries. Though the surface state induced luminescence quenching in nanophosphors could be compensated to some extent by incorporating activators like rare-earth ions, or by exploiting their quantum size effect, obtaining nanophosphors with quantum efficiencies as high as their bulk counterparts remained elusive. In the present communication we report on the synthesis of uniform Eu-doped Y2O3 nanoparticles of 20 - 53 nm size range with down conversion efficiency as high as 86% utilizing a simple chemical precipitation technique. Along with size control, the effects of Eu3+ content on their emission behaviors have been discussed. We believe the low-cost synthesis of these nanoparticles would greatly enhance their application potentials in optical display and bio-imaging technologies.
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Chapter 3: Effect of different additives on the size control and emission properties of Y2O3:Eu3+ nanoparticles prepared through the co-precipitation method: Nanoparticles of europium doped yttrium oxide (Y2O3:Eu3+) were synthesized by the co-precipitation method using oleic acid as a surfactant in the presence of other additives. Incorporation of additives like ethylenediaminetetraacetic acid (EDTA) and NaCl in the reaction mixture drastically affects the particle size, size homogeneity, and emission behavior of the nanophosphors. Photoluminescence emission of the nanophosphors drastically enhances and quenches on addition of NaCl and EDTA in the reaction mixture, respectively. Such emission behaviors of the nanophosphors are explained considering the nephelauxetic effect induced by the incorporated ions in the reaction solution.
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Chapter 5: Synthesis of monodispersed red emitting LiAl5O8:Fe3+ nanophosphors: Efficient wavelength converting nanophosphors are of high demand for their applications in energy conversion devices. We report on the synthesis of well dispersed LiAl5O8:Fe3+ nanoparticles of homogeneous size and different morphologies by sol？gel method suitable for efficient wavelength converting devices. Nanoparticles of phase pure Fe3+ doped LiAl5O8 with different shapes and sizes were obtained by varying the pH of the solution in the range of 3？11. X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy were used to analyze the structure, morphology and composition of the nanoparticles. Incorporation of Fe3+ ions in the LiAl5O8 host lattice has been studied using X-ray photoelectron spectroscopy and electron spin resonance spectroscopy. Emission behavior of the nanophosphors has been studied at room temperature using photoluminescence spectroscopy.
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Chapter 6: Wavelength conversion using rare earth and transition metal doped oxides in polyolefin based nanocomposite films Nanocomposites are a new class of polymeric materials which include organic or inorganic nano-phase materials. These nanocomposite films can show interesting properties which have many applications for wavelength conversion and energy saving. In this paper, we present polyolefin based nanocomposite films prepared using wavelength-converting red ‘phosphors’ such as Y2O3: Eu3+ and LiAl5O8:Fe3+. The durability of the polymer chain is unaffected by incorporation of inorganic nanoparticles as there is no direct interaction between them. The addition of surfactant in the nanocomposite film helps to improve the dispersion ability of the nanoparticles and increase the flexibility of the polymer film. Wavelength-converting ‘nanophosphors’ incorporated in a polymer matrix help to increase the tensile strength of the film. The films show excellent wavelength conversion ability of UV light into the visible and near IR range. These nanocomposite films have great application in energy saving devices.
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