Synthesis of multi-color emitting upconversion nanophosphors and their applications for bioimaging and transparent display

다국어 초록 (Multilingual Abstract)

Phosphors absorb external energy and emit visible light, and they are applied in various fields such as displays, lighting devices, and bio applications. Well-known luminescent materials, quantum dots and organic dyes emit longer wavelength light than absorbed light. On the other hand, upconversion nanophosphors (UCNPs) shown anti-Stokes shift emission that emit light at wavelengths shorter than the wavelengths they absorb. In particular the lanthanide doped UCNPs absorb near-infrared light and emit visible light. In addition, lanthanide doped UCNPs have several advantages like long life times, high-photo stability, and non-blinking. Thus the UCNPs can be used in a variety of applications such as a security, a RGB printing, a transparent display, and bio-imaging.
Lanthanide doped UCNPs have low cytotoxicity for cellular and biological molecules. UCNPs also show luminescence under NIR excitation. Excitation in the NIR region improves transmission of the light source into biological tissue and minimizes the autofluorescence of the biological molecules. Therefore, UCNPs are very suitable for bio-imaging applications.
In the past, the glasses should be existed to see three-dimensional (3D) images, but nowadays, 3D displays without glasses have been developed. Volumetric 3D transparent displays do not require glasses and are used for education, data visualization, and medical imaging. UCNPs are also suitable for 3D transparent displays because UCNPs absorb invisible near-infrared light and emit visible light.
This thesis contains synthesis of color-tunable UCNPs and their applications for bio-imaging and transparent display. Chapter 2 describes the synthesis of sub-10 nm sized LiYF4 based core/shell (C/S) structured UCNPs. C/S UCNPs shows blue to green emission under 980 nm NIR light. Chapter 3 presents the synthesis of green to red emitting NaGdF4 based UCNPs and red emitting core/double-shell (C/D-S) UCNPs under 800 nm NIR light. Red-emitting C/D-S UCNPs were used for in-vivo imaging. Chapter 4 describes the synthesis of red-emitting LiErF4-based core/triple-shell (C/T-S) UCNPs with red emission. Surface modification of UCNPs was performed and applied to in-vivo imaging. Chapter 5 introduces the synthesis of color tunable LiGdF4-based UCNPs. Blue-emitting C/D-S, red, green, and white emitting-C/T-S UCNPs were synthesized. UCNP-polymer composites were fabricated and displayed blue, red, green, and white-emitting luminescence under 980 nm irradiation.

목차 (Table of Contents)

• CHAPTER I. INTRODUCTION 1
• 1.1 Luminescence mechanisms of UCNPs 2
• 1.2 General preparation of lanthanide doped UCNPs 4
• 1.2.1 Synthesis method of UCNPs 4
• 1.2.2 Morphology and nanostructure control 7
• 1.2.3 Surface modification 9
• 1.3 Luminescence characteristics of lanthanide doped UCNPs 14
• 1.3.1 Enhancing Upconversion photoluminescence 14
• 1.3.2 Color tuning of UCNPs 17
• 1.4 Application of UCNPs 24
• 1.4.1 Bio-imaging using UCNPs. 24
• 1.4.2 Transparent display application using UCNPs 27
• 1.5 Outline of thesis 30
• 1.6 References 32
• CHAPTER II. Synthesis of multicolor emission ultrasmall LiYF4-based upconversion nanophosphors with sub-10 nm size . 37
• CHAPTER III. Synthesis of color tunable NaGdF4-based core/double-shell UCNPs and application of in-vivo bio-imaging 63
• CHAPTER IV. Synthesis of red emitting LiErF4-based UCNPs and their surface modification for bio-imaging application 99
• CHAPTER V. Synthesis of color-tunable UCNPs via energy migration and their transparent display application. 137
• CHAPTER VI. Conclusion. 173