[1] Heo J 2002 C. R. Chim. 5 739

[2] Fujimoto Y and Nakatsuka M 2003 Appl. Phys. Lett. 82 3325

[3] Peng M Y, Qiu J R, Chen D P, Meng X G, Yang I Y, Jiang X W and
Zhu C S 2004 Opt. Lett. 29 1998

[4] Meng X G, Qiu J R, Peng M Y, Chen D P, Zhao Q Z, Jiang X W and Zhu
C S 2005 Opt. Exp. 13 1635

[5] Meng X G, Qiu J R, Chen D P, Zhao Q Z, Jiang X W and Zhu C S 2005
Opt. Exp. 13 1628

[6] Ren J, Yang G, Zeng H, Zhang X H, Yang Y X and Chen G R 2006
J. Am. Ceram. Soc. 89 2486

[7] Koughia K, Singh J, Kasap S O and Ruda H E 2006 Optical
Properties of Condensed Matter and Application ed Singh J (New York:
Wiley) chap 2 p 31

[8] Wang J, Brocklesby W S, Lincoln J R, Townsend J E and Payne D N
1993 J. Non-Cryst. Solids 163 261

[9] Fragoso W D, Donega C M and Long R L 2003 J. Lumin.
105 97

[10] Ren J J, Yang I Y, Qiu J R, Chen D P, Jiang X W and Zhu C S 2006
Solid State Commun. 140 38

[11] Peng M Y, Chen D P, Qiu J R, Jiang X W and Zhu C S 2007 Opt.
Mater. 29 556

[12] Beutel M, Setzer K D, Shestakov O and Fink E H 1996 J.
Mol. Spectrosc. 175 48

[13] Shestakov O, Breidohr R, Demes H, Setzer K D and Fink E H
1998 J. Mol. Spectrosc. 190 28

[14] Yang Z Y, Luo L and Chen W 2006 J. Opt. Soc. Am. B
23 358