1. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Aoba, Sendai 980-8577, Japan
2. Applied Spectroscopy Systems Department, Hamamatsu Photonics K. K., Higashiku, Hamamatsu 431-3196, Japan
3. LED Materials Department, Mitsubishi Chemical Corporation, Ushiku, Ibaraki 300-1295, Japan