Micro/nano-structured phosphor materials for white light-emitting diodes and biomedical applications

다국어 초록 (Multilingual Abstract)

The fascinating scientific and technological developments, especially, the
rapidly growing technology in the solid-state lighting market creates a need for the development of novel phosphors with high conversion efficiencies, excellent thermal quenching behavior and the proficient emissions in the visible spectral range. Particularly, oxide-based phosphors activated with trivalent rare-earth ions are recognized as promising materials for next-generation display devices and white
light-emitting diodes due to their environmental friendly nature with stable physical and chemical properties. Currently, a big challenge is to develop novel phosphor materials with high efficiency, thermal stability and reliability for indoor and outdoor illuminations.
Besides, efforts have been focused on the development of nontoxic
multifunctional mesoporous materials for biomedical applications. Several biocompatible materials with different morphologies and compositions, such as metals, metal oxides, and polymers, have been employed as multifunctional biomaterials to target cancer and other diseased cells. Due to the lack of permeable capability, the majority of these materials concentrate in the cytoplasm. Therefore, research efforts have been focused on targeting the cell nucleus by improving the
penetration capability of the particles.
In this thesis, various trivalent rare-earth ions (Eu3+, Tb3+, Sm3+, Dy3+, Er3+, Tm3+, and Yb3+) activated SrY2O4 (SY) nanocrystalline phosphors were synthesized using a modified sol-gel technique. The X-ray diffraction (XRD) patterns confirmed their orthorhombic structure and scanning electron microscope (SEM) image showed the closely packed particles. SY: Eu3+ phosphor showed the reddish-orange emission and SY: Tb3+ phosphor exhibited the bright green color. For the first time, in the case of Eu3+/Tb3+ ions co-doped SY phosphors, concentration independent white light emission was achieved by controlling the energy transfer between Tb3+ and Eu3+ ions and excitation induced emissions were observed from the Sm3+ co-doped SY: Tb3+ phosphor. The Er3+ ions doped phosphors displayed intense green emission and Dy3+/Er3+ ions co-doped phosphors showed yellowish green emission. While, the Er3+/Dy3+/Sm3+ ions triple-doped SY phosphors exhibited a fair white light emission due to the energy transfer from both Dy3+ and Er3+ ions to Sm3+ ions. The upconversion emission properties were also studied for Er3+/Tm3+/Yb3+ ions tri-doped SY host lattice at different pump powers. The achieved results suggest that these SY nanocrystalline phosphors were efficient materials for solid-state lighting applications.
It is well known that, the phosphors with spherical morphology have many advantages like higher packing density, lower scattering of light, and brighter luminescence performance. Also, the suitable morphology and excitation wavelengths are very important for mixing with Y3Al5O12 (YAG):Ce3+ to generate perfect white light emission. In this context, we established the synthesis of Eu3+ ions activated Y2Ti2O7 spheres with two efficient excitations in the excitation and
emission regions of YAG:Ce3+. Likewise, Eu3+ ions doped Gd2O3 nanoflowers were synthesized by facile large-scale route. The structural and morphological properties were carried out by XRD and SEM investigations. The emission intensity and asymmetric ratio between red and orange (R/O) are higher for our Gd2O3:Eu3+ when
compared with the commercial Y2O3:Eu3+.
Nowadays, there is increasing demand for novel yellow phosphor materials with excitation in near-ultra violet (UV) region. So, a novel self-activated yellow Ca5Zn3.92In0.08(V0.99Ta0.01O4)6 (CZIVT) phosphor which efficiently convert violet excitation light into yellow luminescence was synthesized. The crystal structure and
lattice parameters of these CZIVT phosphors are elucidated by Rietveld refinement. By doping the In3+ and Ta5+ ions, the emission intensity is enhanced in the red region and the Stokes shift is controlled to acquire good color rendition. When a near-UV LED chip is coated with the combination of CZIVT and commercial blue phosphors, a pleasant WLED is achieved with high CRI of 82.51 and low CCT of 5231 K which are essential for indoor illuminations.
In this present study, we reported the PEGylated -Gd2(MoO4)3 (GMO) ternary complex compound mesoporous flowers using two-step synthesis such as solvothermal for amorphous precursor and hydrothermal for crystalline with PEGylated precursor. The growth mechanism of flower-like morphology has been explained by taking SEM images of the intermediate products. PEGylation was verified by the XRD patterns and FTIR spectra and the nitrogen adsorptiondesorption isotherms of PEGylated -GMO particles established their mesoporous nature. When exciting with UV or visible wavelengths these mesoporous particles displayed gorgeous red emission. These mesoporous particles are proved to be promising biomaterials with hydrophilic nature and have the capacity to penetrate
cells, translocate to the nucleus, and trigger high-quality signals from the cellular compartment than earlier nanoparticles. Likewise, size tunable mesoporous Gd:Eu3+@mSiO2@FA core-shell nanoparticles were synthesized and these core-shell nanoparticles exhibited high quality red emission in the near-UV and visible regions. The preliminary results confirmed that, after conjugated with folic acid, increased number of Gd:Eu3+@mSiO2@FA core-shell nanoparticles were entered in to the both nuclear and cytoplasm in U2OS cell lines due to the increased hydrophilic nature of the particles.

목차 (Table of Contents)

• Chapter 1
• 1. Introduction 1
• 1.1. The basic mechanism of luminescence 1
• 1.2. Luminescence theory of rare-earth ions 4
• 1.2.1. Properties of Rare-earth ions 7
• 1.2.2. Selection rules of rare-earth ions 8
• 1.2.3. Applications of rare-earth ions in optical materials 11
• 1.3. Luminescence mechanism in phosphors 12
• 1.3.1. Excitation mechanism of phosphors 13
• 1.3.2. Emission mechanism of phosphors 16
• 1.4. Applications of phosphors 18
• 1.4.1. Significance of phosphor host matrix for solid-state lighting applications 20
• 1.4.2. Significance of mesoporous /PEGylated materials for biomedical applications 21
• References 23
• Chapter 2 26
• 2. Various Rare-earth ions Activated SrY2O4 Phosphor for Monochromatic and White-light Based Solid-state Lighting Applications 26
• 2.1. Synthesis of SY:RE3+ by a sol-gel method 27
• 2.2. Structural studies of SY nanocrystalline phosphors 28
• 2.3. A novel Strategy for controllable emissions from Eu3+ or Sm3+ ions co-doped SY:Tb3+ phosphors and tunable emissions from Dy3+/Sm3+/Er3+ ions tri-doped SY phosphors 31
• 2.3.1. Emission investigation of Eu3+ ions activated SY 31
• 2.3.2. Emission analysis of Tb3+ ions activated SY 36
• 2.3.3. Emission analysis of Sm3+ ions doped SY 40
• 2.3.4. Luminescent properties of Sm3+ ions activated SY 43
• 2.3.5. Luminescent exploration of Er3+ ions activated SY 45
• 2.3.6. Controllable energy transfer between Tb3+ and Eu3+ ions: an approach for concentration independent white-light emission 48
• 2.3.7. Luminescent study of Tb3+ and Sm3+ ions co-activated SY phosphors 52
• 2.3.8. Emission analysis of Er3+ and Dy3+ ions co-activated SY 58
• 2.3.9. Warm white-light emission from Er3+/Dy3+/Sm3+ ions triple-doped SY phosphors 61
• 2.4. Pump power induced tunable up-conversion emissions from Er3+/Tm3+/Yb3+ ions tri-doped SY nanocrystalline phosphors 64
• 2.4.1. Up-conversion (UC) emission analysis of Er3+ ions single-doped SY phosphors 64
• 2.4.2. UC emission Study of 1Er3+/3Yb3+ ions co-doped SY 65
• 2.4.3. UC emission investigation of 1Er3+/1Tm3+/3Yb3+ ions tri-doped SY 67
• 2.4.4. UC emission efficiency versus pump power analysis 71
• 2.5. Conclusion 74
• References 76
• Chapter 3 80
• 3. Nanoparticles Synthesis by Novel Wet-chemical Methods 80
• 3.1. Solvothermal synthesis and luminescent properties of Y2Ti2O7:Eu3+ spheres 81
• 3.1.1. Synthesis of YT:Eu3+ spheres by a solvothermal route 81
• 3.1.2. Morphological and structural evaluation of YT:Eu3+ spheres 82
• 3.1.3. Luminescent examination of YT:Eu3+ spheres 85
• 3.2. A facile large-scale synthesis and luminescence properties of Gd2O3:Eu3+ nanoflowers 88
• 3.2.1. Synthesis of Gd2O3:Eu3+ nanoflowers by a facile large-scale technique 88
• 3.2.2. Morphological and structural analysis of Gd2O3:Eu3+ nanoflowers 89
• 3.2.3. Luminescent study of Gd2O3:Eu3+ nanoflowers 93
• 3.3. Conclusion 95
• References 96
• Chapter 4 98
• 4. Rare-earth Free Novel Yellow CZIVT Phosphor for Dazzling White Light-Emitting Diodes 98
• 4.1. Experimental procedure 99
• 4.1.1. Synthesis of yellow phosphor by sol-gel route 99
• 4.1.2. Fabrication of phosphor-converted (pc)-LEDs 100
• 4.2. Morphological and structural properties of CZIVT phosphors 101
• 4.3. Luminescent analysis of CZIVT phosphors 107
• 4.4. Fabrication and electroluminescence analysis of pc-LEDs 116
• 4.5. Investigation of CRI, CCT, and CIE values 119
• 4.6. Conclusion 121
• References 122
• Chapter 5 124
• 5. Mesoporous Nanoparticles for Bioimaging Applications 124
• 5.1. PEGylated -Gd2(MoO4)3 mesoporous flowers: its synthesis, characterization and biological applications 125
• 5.1.1. Experimental procedure 125
• 5.1.2. Morphological and structural properties of GMR marigold-like flowers 127
• 5.1.3. Luminescent properties of GMR marigold-like flowers 137
• 5.1.4. Bioimaging (in vitro) properties of GMR flowers 139
• 5.2. Size tunable Gd:Eu3+@mSiO2@FA core-shell mesoporous particles for bioimaging applications 142
• 5.2.1. Experimental Procedure 142
• 5.2.2. Morphological and structural properties of Gd@mSi core-shell nanoparticles 146
• 5.2.3. Luminescent study of Gd@mSi Core-Shell nanospheres and nanoparticles 149
• 5.2.4. Bioimaging (in vitro) properties of Gd@mSi and Gd@mSi@FA core-shell nanoparticles 152
• 5.3. Conclusion 155
• References 157
• Chapter 6 161
• Conclusions 161
• Appendix
• List of Publications 164