| Author: | Li, Hiu-ling |
| Title: | Luminescence of phosphors based on novel oxides for field emission display |
| Degree: | M.Phil. |
| Year: | 2009 |
| Subject: | Hong Kong Polytechnic University -- Dissertations Phosphors. Luminescence. Metallic oxides Field emission |
| Department: | Department of Applied Physics |
| Pages: | x, 90, xii leaves : ill. (some col.) ; 31 cm. |
| Language: | English |
| Abstract: | This thesis presents studies on the synthesis, structural and optical characterization of rare-earth doped tungstates and binary oxide phosphors. Photoluminescence (PL) and low-voltage cathodoluminescence (CL) are used to investigate these promising phosphors for use in field emission display. The imperfection performance of sulfide-base phosphors has motivated us to investigate the more chemically and physically stable oxide-based phosphors. In our work, a variety of properties of the phosphors were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, low-voltage CL, PL spectra and lifetime. In our work, the luminescent properties of BaWO₄-based and ZnWO₄-based phosphors were investigated. Rare-earth ions (Eu³⁺ , Tb³⁺ , Tm³⁺) doped BaWO₄phosphors were prepared by a polyol-mediated method. Spherical morphology of the scheelite-structured particles was observed. While excited by ultra-violet (UV) light or low-voltage electron beam, red, green and blue emissions were observed in Eu³⁺, Tb³⁺ and Tm³⁺ doped phosphors, respectively. These emissions are attributed to the characteristic intraconfigurational 4f transitions in Eu³⁺, Tb³⁺ and Tm³⁺. Among them, the luminance of BaWO₄: Tb³⁺ was as high as 4866 cd/m² under excitation of electron beam (4.5 kV). The investigation on the chromaticity of BaWO₄: Tm³⁺ indicated that it had extremely high color purity (97%) and showed its potential as a promising blue-emitting phosphor. For the Eu³⁺ doped BaWO₄, very high intensity ratio of ⁵D₀ → ⁷F₂and ⁵Do → ⁷F₁transitions (R-value) indicates that Eu³⁺ ions may locate at a crystallographic site without inversion symmetry. Wolframite nanostructural ZnWO₄and ZnWO₄: Eu³⁺ were synthesized by refluxing in a water solution and followed by annealing at different temperatures. Different colors of emission were observed from the ZnWO₄- based phosphors. Blue-green CL emission of the annealed ZnWO₄is attributed to the highly emissive WO⁶⁻₆ ion complex. As-synthesized and annealed ZnWO₄: Eu³⁺ phosphors exhibit red and white emissions, respectively. The dynamic of emissions between WO⁶⁻₆ ion complex and Eu³⁺ ions with increasing annealing temperature were discussed. Luminescence of binary oxides was also studied in this work. A urea precipitation method was used to synthesize nanostructural ZrO₂: RE³⁺ (RE=Eu, Tb, Tm) phosphors. The characteristic red-green-blue (RGB) emissions of the rare earth ions were observed in the PL spectrum. Comparing to BaWO₄: Eu³⁺, ZrO₂: Eu³⁺ phosphor has a relatively small R-value, which indicates that Eu³⁺ ions may be distorted slightly and occupy a site without inversion symmetry. Similar result was observed in the CL spectrum. Regarding the Tm³⁺ doped ZrO₂, both emissions from defects of ZrO₂and Tm³⁺ ions was observed; however, such emission was observed in CL. Intrinsic emission in ZnO was also studied via PL and CL. Different morphologies of ZnO particles were synthesized by a hydrothermal method. Defect-related emission of the ZnO particles as a function of crystal size and morphology was discussed. |
| Rights: | All rights reserved |
| Access: | open access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| b2343000x.pdf | For All Users | 14.64 MB | Adobe PDF | View/Open |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/5671