Fabrication and Luminescence Characterization of Rare Earth Based Phosphors for X-ray Imaging : X-선 영상을 위한 희토류계 형광체의 제조와 발광 특성

국문 초록 (Abstract)

이 연구는 디지털 방사선 영상 및 X-선 영상판 및 증감지 등의 의료 방사선 영상에 사용되는 새로운 형광체를 개발하는 것이 주목적이다. 형광체는 이 밖에도 다양한 산업 분야 즉, 램프나 플라즈마 디스플레이, 레이저 물질, 음극관 튜브 및 비파괴 검사 분야에서 다양하게 이용된다. 이 실험에서Eu 또는Sm 이 도핑된 LLBO (Li6Lu(BO3)3) 와 Ln3+ 이 도핑된 Gd2GeO5, Eu 또는 Ce 이 도핑된 GGAG (Gd3Ga2Al3O12) 그리고 Gd를 도핑한 LYBO (Li6Y(BO3)3) 을 각각 제조하였다. 이 원료 물질들은 희토류계 원소로 다른 물질과 비교하여 높은 유효 원자번호를 가지기 때문에 의료 방사선 영상 분야에서 사용되는 X-선과 감마선에 대한 흡수효율이 매우 우수하다. 높은 순도의 주 물질과 활성제로 이루어진 대부분의 형광체는 고체 반응법을 이용하여 전기로에서 높은 온도로 소성한다. 그런 다음 제조된 형광체는UV, X-선 그리고, 양성자선을 이용하여 발광 스펙트럼 특성을 조사하였으며, 형광 붕괴 시간, 상대적 발광량, 엑스선회절시험 (X-ray diffraction, XRD), 전계방사형주사전자현미경(field emission scanning electron microscope, FE-SEM) 등을 측정하였다. 제조된 형광체의 각각의 발광 스펙트럼은 대략 500~700 nm로 장파장 영역에서 발생하였으며 이것은 광전자증배관(PMT)과 같은 광 센서보다 전하결합소자 (charge coupled device, CCD), 상보성금속산화 (complementary metal-oxide semiconductor; CMOS) 소자, 광다이오드 (photodiode, PD) 혹은 박막트랜지스터(thin film transistor, TFT) 와 같은 광센서의 양자효율 특성에 잘 매칭되므로 이들 수광 소자를 이용한 X=선 영상 장비에 유용하다. 상대적 발광량은 형광체의 특성을 결정하는 가장 중요한 요소 중 하나이다. 실험 결과 GGAG (Gd3Ga2Al3O12) 와 LLBO (Li6Lu(BO3)3) 형광체는 상용화된 가독스(Gd2O2S:Tb) 형광체와 비교하여 높은 효율의 빛을 방출하였다.

다국어 초록 (Multilingual Abstract)

The purpose of this study is to develop the novel phosphor for medical radiographic imaging, such as digital radiography (DR), X-ray imaging plate (IP) and intensifiers etc. Besides, the phosphor can be used various industrial fields, such as various lamps, plasma display, laser materials, cathode-ray tubes and non-destructive inspection and etc.
In this experiment, the novel phosphors such as Eu3+ or Sm3+ doped Lithium Lutetium Borate; LLBO (Li6Lu(BO3)3), Ln3+ doped Gd2GeO5, Eu3+ or Ce3+ doped Gadolinium Gallium Aluminum Garnet; GGAG (Gd3Ga2Al3O12) and Gd3+ doped Lithium Yttrium Borate; LYBO (Li6Y(BO3)3) are fabricated. These raw materials made up of rare earth elements have a high effective Z-number (Zeff) in comparison to other phosphors and the high effective Z-number led to the high absorption efficiency for X-ray or gamma rays in medical radiation imaging fields.
Most of phosphor are synthesized by solid state reaction with high purity of the host and activator materials at high temperature by using electric furnace. Then, the luminescent properties of the phosphor were characterized bys photoluminescence, X-ray induced luminescence, proton induced luminescence, decay time, relative light yield, X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) measurements.
The emission spectra of fabricated phosphors show the long wavelength at 500~700 nm roughly. The long wavelength is well matched to silicon based light sensor such as photo diode (PD), charge coupled devices (CCDs), thin film transistor (TFT) and complementary metal oxide semiconductor (CMOS) sensor because of their high quantum efficiency compared to the photomultiplier tube (PMT) and another light detectors. Therefore fabricated phosphors are suitable for X-ray imaging application using CCD, CMOS, PD or TFT which is the high quantum efficiency in the wavelength range of 500~700 nm.
The relative light yield is one of the most important parameter to determine the characteristic of phosphor. As a result, GGAG (Gd3Ga2Al3O12) and LLBO (Li6Lu(BO3)3) phosphor shows the high effective light compared to reference phosphor such as Gadox (Gd2O2S:Tb).

목차 (Table of Contents)

• CHAPTER Ⅰ 1
• INTRODUCTION 1
• CHAPTER Ⅱ 4
• THEORY 4
• 2.1. Radiation interaction with matter 4
• 2.1.1. Interaction of gamma-rays 5
• 2.1.2. Interaction of neutrons 10
• 2.2. Fundamentals of luminescence 13
• 2.2.1. The energy band structure 14
• 2.2.2. The energy level of phosphor 16
• 2.2.3. The selection rules 24
• 2.2.4. The f-f and f-d transitions of lanthanide 26
• 2.2.5. The Dieke diagram 28
• 2.2.6. The energy level of various trivalent rare-earth ions 31
• 2.3. The Luminescence characterization of phosphor 54
• 2.3.1. Decay time 54
• 2.3.2. Light yield 55
• 2.3.3. Quantum efficiency 57
• 2.3.4. Radiation damage 58
• 2.3.5. γ-ray absorption power 59
• 2.3.6. Quenching mechanism 60
• 2.3.7. Cost consideration 62
• 2.4. Application of phosphors in medical fields 63
• 2.4.1. Computed tomography (CT) 64
• 2.4.2. Digital radiography (DR) 65
• CHAPTER Ⅲ 70
• EXPERIMENTAL TECHNIQUES 70
• 3.1. Sample preparation 70
• 3.2. Measurement systems 72
• 3.2.1. X-ray induced luminescence spectrum 73
• 3.2.2. Photoluminescence spectrum 74
• 3.2.3. Proton induced emission spectrum 75
• 3.2.4. X-ray diffraction (XRD) 75
• 3.2.5. Field emission scanning electron microscopy (FE-SEM) 77
• CHAPTER Ⅳ 78
• THE LUMINESCENCE PROPERTIES OF Ln3+ DOPED Gd2GeO5 PHOSPHOR 78
• 4.1. The fabrication and measurement of Ln3+ doped Gd2GeO5 phosphor 78
• 4.2. Results 80
• 4.2.1. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) 80
• 4.2.2. Luminescence spectra of Eu3+ doped Gd2GeO5 phosphor 81
• 4.2.3. Luminescence spectra of Dy3+ doped Gd2GeO5 phosphor 83
• 4.2.4. Luminescence spectra of Tb3+ doped Gd2GeO5 phosphor 85
• 4.2.5. Luminescence spectra of Sm3+ doped Gd2GeO5 phosphor 87
• 4.2.6. Relative light yield 90
• CHAPTER Ⅴ 91
• THE PROPERTIES OF Eu3+ or Ce3+ DOPED GGAG (Gd3Ga2Al3O12) PHOSPHOR 91
• 5.1. The fabrication and measurement of Eu3+ or Ce3+ doped GGAG (Gd3Ga2Al3O12) phosphor 92
• 5.2. Results 93
• 5.2.1. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) 93
• 5.2.2. Luminescence spectrum 95
• 5.2.3. Relative light yield 101
• CHAPTER Ⅵ 102
• THE PROPERTIES OF Eu3+ OR Sm3+ DOPED LLBO (Li6Lu(BO3)3) PHOSPHOR 102
• 6.1. The fabrication and measurement of Eu3+ or Sm3+ Li6Lu(BO3) 3 phosphor 103
• 6.2. Results 105
• 6.2.1. X-ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM) 105
• 6.2.2. Luminescence spectrum 107
• 6.2.3. Relative light yield 112
• CHAPTER Ⅶ 114
• THE PROPERTIES OF Gd3+ DOPED LYBO (Li6Y (BO3)3) PHOSPHOR 114
• 7.1. The fabrication and measurement of Gd3+ doped Li6Y (BO3) 3 phosphor. 115
• 7.2. Results 117
• 7.2.1. X-ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM) 117
• 7.2. 2. Luminescence spectrum 118
• 7.2. 3. Relative light yield 121
• CHAPTER Ⅷ 123
• CONCLUSIONS 123
• REFERENCES 128
• ABSTRACT(Korean) 135
• ACKNOWLEDGEMENTS 138