1. Y. Kan, H.F. Bo, X.M. Lu et al., Appl. Phys. Lett. 172910, 92 (2008)
2. X.K. He, K. Li, M. Liu et al., Opt. Commun. 2531, 281 (2008)
3. S.H. Yao, J.Y. Wang, H. Liu et al., J. Alloy. Compd. 501, 455 (2008)
4. D. Xue, K. Kitamura, J. Cryst. Growth 507, 249 (2003)
5. K. Niwa, Y. Furukawa, S. Takakawa, K. Kitamura, J. Cryst. Growth 493, 208 (2000)