[1] [1] Miyajima Y, Sugawa T, Fukasaku Y. Electron. Lett., 1991, 27: 1706.

[2] [2] Chen J, Gong X, Lin Y, et al. J. Alloys Compd., 2010, 492: 667.

[3] [3] Pappalardo R. J. Lumin., 1976, 14: 159.

[5] [5] Peacock R D. Struct. Bond.， 1975, 22: 83.

[6] [6] Dunina E B, Kaminskii A A, Kornienko A A, et al. Sov. Phys. Solid State, 1990, 32: 920.

[7] [7] Chen X B, Song Z F, Hu L L, et al. Opt. Express, 2007, 15: 13422.

[8] [8] Génova R T, Martin I R. Journal of Alloys and Compounds, 2004, 380: 167.

[9] [9] Carnall W T, Fields P R, Rajnak K. J. Chem. Phys., 1968, 49: 4412.

[10] [10] Weber M J. J. Chem. Phys., 1968, 48: 4774.

[11] [11] Kuck S, Sokolska I, Henke M. Phys. Rev. B, 2005, 71: 165112.

[12] [12] Jorgensen C K, Reisfeld R. J. Less-Common Met., 1983, 93: 107.

[13] [13] Quimby R S, Tick P A, et al. J. Appl. Phys., 1998, 83(3): 1648.

[14] [14] Wang Y, Li J F, You Z Y, et al. J. Alloys Compd., 2010, 502: 184.

[15] [15] Weber M J, Varitimos T E, Matsiner B H. Phys. Rev. B, 1973, 8: 47.

[16] [16] Cao J F, Wang Y, Ma X H, et al. J. Alloys Compd., 2011, 509: 185.

[17] [17] Maria C, Sabina B. Optical Materials, 2009, 31: 1898.

[18] [18] Krupke W F. IEEE J. Quantum Electron., 1974, 10: 450.