[1] Venkatachalam N, Saito Y, Soga K. Journal of American Ceramic Society, 2009, 92(5): 1006.

[2] Eilers H. Journal of Alloys and Compounds, 2009, 474(1-2): 569.

[3] Martín-Rodríguez R, Valiente R, Pesquera C, et al. Journal of Luminescence, 2009, 129(9): 1109.

[4] Fang L Shuang, et al. Optics Express, 2010, 18(3): 2309.

[5] Sharma P K, Jilavi M H, Varadan V K, et al. Journal of Physics and Chemistry of Solids, 2002, 63(1): 171.

[6] Muresan L, Popovici E J, Grecu R, et al. Journal of Alloys and Compounds, 2009, 471(1-2): 421.

[7] Wu Y, Li J, Pan Y, et al. Ceramics International, 2009, 35(1): 25.

[8] Chen Q, Shi Y, An L, et al. Journal of American Ceramic Society, 2006, 89(6): 2038.

[9] Saito N, Matsuda S I, Ikegami T. Journal of American Ceramic Society, 1998, 81(8): 2023.

[12] Tanner P A, SUN Waiyin. Journal of Materials Science, 2001, 36(9): 2253.