Luminescent and Structural Analysis of Nanosized Yttrium Aluminum Garnet and Barium Magnesium Aluminate Phosphors Using Synchrotron Radiation Techniques
Date Issued
2004
Date
2004
Author(s)
Huang, Chien-Hao
DOI
en-US
Abstract
Human culture has developed in accordance with communication skills by voice, letter, telephone, radio, and television. TV now is not only a necessary commodity in modern life for communication and entertainment but also one of the most important human-machine interfaces in our daily life. With the progress of technology, various new displays have been developed. The plasma display panel is one of the most promising candidates for its low weight, thinner volume, large view angle, high contrast. Phosphors, which absorb certain energy and emit the energy as visible radiation, play an important role in these newly developed displays.
In this thesis, the solid-state-reaction method and the emulsion process were firstly adopted to prepare the europium-doped yttrium aluminum garnet, which is an important red PDP phosphor. It is observed that the reaction routes are different for the phosphors synthesized via these two processes. Through emulsion method, phase-pure and closely spherical YAG: Eu3+ phosphors with submicron particle size were obtained after calcination at 1400˚C. The morphology and particle size distribution of emulsion-derived phosphors are superior to those obtained via solid-state reaction. From the emission spectra upon the ultra-violet and vacuum ultra-violet radiation, it is found that emulsion-derived YAG: Eu3+ exhibits better luminescent properties.
The reverse-microemulsion technique was employed to prepare nanosized YAG: Eu3+. The application of the obtained YAG: Eu3+ phosphors on plasma display panels as red component was examined through the measurement of emission spectra under the excitation of VUV radiation. The synthesis temperature of YAG: Eu3+ phosphor was reduced to 1100˚C, and well-dispersed, spherical particles (~30 nm) were obtained. The luminescent intensity of YAG: Eu3+ increased with the rise of calcined temperature due to the increase of the crystallinity of the obtained powders. The concentration quenching phenomenon was observed for the samples with Eu3+ concentration higher than 5%. Moreover, increasing the water to oil ratio (W/O) volume ratio resulted in an increase in the particle size and loss in spherical morphology. The luminescent intensity also reduced with increase in the W/O volume ratio. To investigate the effect of local environment on Eu3+ activators in YAG, X-ray absorption techniques were applied to investigate the local structure, electronic structure, atomic structure disorder, and long range ordering. According to the above results, this technique was considerable to be valuable in synthesizing nanosized phosphors; thereby, gadolinium-ion co-doped YAG: Eu3+ phosphors were prepared via this process. With increase in the Gd3+ doping concentration, the particle size and the morphology of YAG: Eu3+ remained unchanged. However, there are obvious sensitized-enhancements in the luminescence intensity, quantum efficiency, and chromacity.
In the third part of this thesis, europium-doped barium magnesium aluminate (BAM: Eu2+) blue phosphors were prepared via a sol-gel polymer process employing citric acid and ethylene glycol as polymerizing agents. Phase-pure BAM: Eu2+ could be obtained after calcination at 1400˚C. It is observed that after calcined in reducing atmosphere, BAM: Eu2+ exhibits intensive and blue Eu2+ emission while samples before reducing treatment exhibit weak and red Eu3+ emission. The electron paramagnetic resonance (EPR) spectra confirmed the presence of Eu2+ ions in samples subjected to reducing atmosphere. The Eu2+ signals in sol-gel derived samples suggested the lower symmetry of Eu2+ ions in these samples. In samples subjected to additional 500˚C heat-treatment. The EPR signals for Eu2+ ions were reduced indicating that oxidation of Eu2+ took place to form Eu3+. Furthermore, Eu2+ ions substituted into different sites also had effects on the thermal stability.
Subjects
鎂鋁酸鋇
釔鋁柘榴石
同步輻射
螢光材料
奈米
Nano
Synchrotron radiation
Barium magnesium aluminate
Yttrium aluminum garnet
Phosphor
Type
thesis