Synthesis and Luminescence Properties of Lanthanide Doped Oxide Phosphors
- Abstract
- Lanthanide ion doped oxide phosphors are an important family of inorganic materials that have been widely used as light emitting devices, catalysts, magnetic materials, fluorescent labels for biological detection and other functional materials based on the electronic, optical and chemical characteristics resulting from their unique 4f electron configuration.
This thesis reports the synthesis and luminescent properties of lanthanide doped and co-doped oxide phosphors (SrAl2O4:Eu2+, CaGd4O7:Eu3+, Sr2CeO4 and Sr2CeO4:Er3+/Yb3+). The oxide phosphors were prepared by solid state reaction, solvothermal method and high-energy ball milling method, respectively.
Initially, Eu2+ doped SrAl2O4 phosphor was prepared by using H3BO3 as flux. The prepared phosphor showed a pure monoclinic SrAl2O4 phase without any other phases as impurity and exhibited an improved crystallinity of the phase. Moreover, the addition of an appropriate amount of flux enhanced the luminescence intensity of the phosphors and reduced the luminescence quenching.
The trivalent Eu ions (Eu3+) doped CaGd4O7 phosphor was made with various concentrations of dopant. Here, the increase in concentration of Eu3+ ions result with the increasing red emission intensity up to the concentration of 6 mol% which is then starts decreasing from the concentration above 6 mol%. The integrated emission intensity of 6 mol% Eu3+ doped CaGd4O7 phosphor excited at 397 nm is about 2.5 times as that of commercial red phosphor Y2O3:Eu3+.
In the same line, the Sr2CeO4 phosphor was prepared and characterized thoroughly. The PL spectra of this phosphor show a broad emission band with a maximum intensity at 478 nm due to the ligand-to-metal Ce4+ charge transfer. Moreover, the long lifetimes of Sr2CeO4 phosphors are also characteristic of a ligand-to-metal charge transfer emission.
At last, the UC phosphor namely Sr2CeO4:Er3+/Yb3+ was made and analyzed its efficacy. The UC emission intensity of this phosphor mainly depends on the doping concentration of Yb3+ ions. The optimal doping concentration of Yb3+ was found to be 7.5 mol%. The considerable enhancement in UC emission was attributed to the efficient energy transfer between Yb3+ and Er3+. The EBT (4S3/2 + 2F7/2 → 4I13/2 + 2F5/2) process contributed to the increased intensity ratio of the red to green emission in Sr2CeO4:Er3+/Yb3+ phosphors.
- Issued Date
- 2015
- Awarded Date
- 2015. 8
- Type
- Dissertation
- Publisher
- 부경대학교 대학원
- Affiliation
- 물리학과
- Department
- 대학원 물리학과
- Advisor
- 정중현
- Table Of Contents
- Abstract x
I. Introduction 1
II. Background 4
2.1 Definition of phosphor 4
2.2 Up-conversion phosphor 5
2.3 Rare-Earth elements 7
2.3.1 Electronic Configuration 7
2.3.2 Selection rules of rare-earth ions 9
2.3.3 Properties of rare-earth ions 10
2.3.4 Luminescence of specific rare-earth ions 13
2.3.4.1 Eu2+ ion 13
2.3.4.2 Eu3+ ion 15
2.3.4.3 Er3+, Yb3+ ions 16
2.4 Luminescence mechanisms 17
2.4.1 Principle 17
2.4.2 Excitation mechanism 20
2.4.3 Emission mechanism 24
2.5 Charge transfer mechanism 25
2.6 Decay of luminescence 26
2.7 UC mechanisms 27
2.7.1 Single-ion process UC mechanism 30
2.7.2 Multi-ion process UC mechanism 32
2.7.3 Rare-earth upconverters 34
2.8 Application areas of phosphor materials 37
III. Experimental 39
3.1 Experimental method 39
3.1.1 Conventional solid-state reaction and high-energy ball milling method
39
3.1.2 Solvothermal method 41
3.2 Characterizations 43
3.2.1 X-ray diffractometer (XRD) 43
3.2.2 Field emission Scanning Electron Microscope (FE-SEM) 45
3.2.3 Photoluminescence spectroscopy 47
3.2.4 Up-conversion spectroscopy 49
IV. Results and Discussions 50
4.1 SrAl2O4:Eu2+ phosphor 50
4.2 CaGd4O7:Eu3+ phosphor 64
4.3 Sr2CeO4 phosphor 84
4.3.1 Luminescence properties of Sr2CeO4 phosphor 84
4.3.2 UC luminescence properties of Er3+ and Yb3+ co-doped Sr2CeO4 phosphor 101
V. Conclusions 121
References 124
- Degree
- Doctor
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