1. Institute of Electro-Optical Science and Technology, National Taiwan Normal University, Taipei 116, Taiwan
2. Department of Materials Engineering, Kun Shan University, Tainan 710, Taiwan
3. Department of Physics, National Chung Hsing University, Taichung 402, Taiwan
4. Department of Electro-Optical Engineering, Kun Shan University, Tainan 710, Taiwan