1. Department of Materials Science and Engineering, KAIST, 335 Gwahangno, Yuseong-gu, Daejeon, 305-701, South Korea
2. Photonics Technology Research Institute, Department of Materials Science and Engineering, Chonnam National University, 300 Yongbong-Dong, Buk-Gu, Gwangju 500-757, South Korea
3. Department of Physics, Shivaji University, Kolhapur 416 004, M.S., India
4. Development of Advanced Components & Materials, Korea Institute of Industrial Technology, Gwangju,500-480, South Korea