Second-order optical nonlinearities of metastable BiBO 3 phases in crystallized glasses R. Ihara, T. Honma, Y. Benino, T. Fujiwara, T. Komatsu * Department of Chemistry, Nagaoka University of Technology, 1603-1 Kamitomioka-cho, Nagaoka 940-2188, Japan Received 25 November 2003; accepted 11 February 2004 Available online 11 September 2004 Abstract Metastable BiBO 3 and rare-earth (RE)-doped RE x Bi 1Àx BO 3 crystals were prepared through the crystallization of 50Bi 2 O 3 Æ 50B 2 O 3 and xRE 2 O 3 Æ (50Àx)Bi 2 O 3 Æ 50B 2 O 3 glasses (RE = Y, La, Gd, Yb), and their second harmonic (SH) intensities were examined using the Kurtz powder method. It was confirmed that BiBO 3 has two different crystalline forms, i.e., BiBO 3 (I) and BiBO 3 (II), and that BiBO 3 (I) transforms into BiBO 3 (II) at temperatures around 500 °C. Both phases were found to be nonlinear optical crystals with a phase matchable character, and the SH intensity of BiBO 3 (II) powders was approximately 110 times as large as a-quartz powders. The incorporation of RE 3+ into BiBO 3 (II) was confirmed from X-ray dif- fraction analysis, and in particular, Gd x Bi 1Àx BO 3 (II) showed an enhanced SH intensity of approximately 145 times as large as a-quartz. Ó 2004 Elsevier B.V. All rights reserved. PACS: 42.65.Ky; 42.70.Nq; 81.05.Kf; 81.05.Pj Keywords: Second harmonic generation; Bismuth borate crystal; Crystallized glass 1. Introduction The phase diagram of the binary system of Bi 2 O 3 – B 2 O 3 has been examined by Levin and McDaniel [1], and it has been determined that five compounds of 12Bi 2 O 3 Æ B 2 O 3 (i.e., Bi 24 B 2 O 39 ), 2Bi 2 O 3 Æ B 2 O 3 (Bi 4 B 2 O 9 ), 3Bi 2 O 3 Æ 5B 2 O 3 (Bi 3 B 5 O 12 ), Bi 2 O 3 Æ 3B 2 O 3 (BiB 3 O 6 ) and Bi 2 O 3 Æ 4B 2 O 3 (Bi 2 B 8 O 15 ) exist as thermodynamically sta- ble phases. Among these compounds, it is well known that BiB 3 O 6 exhibits a large second-order optical nonlin- earity, and numerous studies on its single crystal growth and optical properties have been carried out [2,3]. On the other hand, Pottier [4] has reported the presence of bismuth orthoborate BiBO 3 as a metastable phase. This phase can be prepared by cooling of a melt with the composition of 50B 2 O 3 Æ 50B 2 O 3 , and it has been con- firmed that the metastable BiBO 3 phase decomposes into a mixture of the stable Bi 4 B 2 O 9 and Bi 3 B 5 O 12 phases at 600 °C [4]. Recently, Becker [5] has reported that the metastable BiBO 3 phase is also obtained through the crystallization of binary Bi 2 O 3 –B 2 O 3 glasses. There has been, however, no report on optical properties of a metastable BiBO 3 phase. Recently, Honma et al. [6–8] have discovered new nonlinear optical crystalline phases RE x Bi 1Àx BO 3 in the crystallized glasses of RE 2 O 3 –Bi 2 O 3 –B 2 O 3 (RE: La, Gd, Sm) and, furthermore, found that some glasses such as 12.5Sm 2 O 3 Æ 30Bi 2 O 3 Æ 57.5B 2 O 3 are crystallized by irradiation of Nd:YAG laser with a wavelength of k = 1064 nm, giving the formation of nonlinear optical crystal dots and lines in the glasses. These results suggest 0925-3467/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2004.07.002 * Corresponding author. Tel.: +81 258 47 9313; fax: +81 258 47 9300. E-mail address: komatsu@chem.nagaokaut.ac.jp (T. Komatsu). www.elsevier.com/locate/optmat Optical Materials 27 (2004) 403–408