[1] J. Qiu and K. Hirao, Solid State Commun. 106, 795 (1998).
[2] J. Qiu, M. Kawasaki, K. Tanaka, Y. Shimizugawa, and K. Hirao, J. Phys. Chem. Solids 59, 1521 (1998).
[3] M. Yamazaki, Y. Yamamoto, S. Nagahama, N. Sawanobori, M. Mizuguchi, and H. Hosono, J. Non-Cryst. Solids 241, 71 (1998).
[4] G. Lin, G. Dong, D. Tan, X. Liu, Q. Zhang, D. Chen, J. Qiu, Q. Zhao, and Z. Xu, J. Alloys Comp. 504, 177 (2010).
[5] C. Li, Q. Su, and S. Wang, Mater. Res. Bull. 37, 1443 (2002).
[7] C. Yu, D. He, G. Wang, J. Zhang, and L. Hu, Chin. Opt. Lett. 8, 197 (2010).
[8] T. Kinoshita, M. Yamazaki, H. Kawazoe, and H. Hosono, J. Appl. Phys. 86, 3729 (1999).
[9] W. Hoogenstraaten, Philips Res. Repts. 13, 515 (1958).