A Model of New VUV NLO Materials Based on Borate: A Novel Noncentrosymmetric Borophosphate Compound Be 3 BPO 7
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A Model of New VUV NLO Materials Based on Borate: A Novel Noncentrosymmetric Borophosphate Compound Be3BPO7 Zhangzhen He† and Hiroshi Moriyama* Department of Chemistry, Toho University, Funabashi 274-8510, Japan † Present Address: Materials & Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
ABSTRACT A favorable borate anionic group can be selected as the basic structural unit for VUV NLO materials, in terms of the properties of known inorganic NLO crystals and the features of their anionic groups, based on anionic group theory from SHG coefficients, UV absorption edge and moderate birefringence. Considering the coordination chemistry of atoms in some inorganic compounds, and the relationship between a noncentrosymmetric structural arrangement and the composition of compounds, a suitable theoretical model that aids the search for new VUV NLO materials has been proposed. The model compounds, formulated as MxA1,2(BO3)1,2Oy, may be prospective candidates for new VUV NLO materials considering their SHG coefficients, UV absorption edge, and moderate birefringence. The model suggests that investigation for a new VUV NLO material would be profitably conducted by focusing on boroberylate, boroaluminate, and borophosphate, on the basis of anionic group theory. For example, a novel noncentrosymmetric beryllium borophosphate compound, Be3BPO7 was synthesized by solidstate reaction. Microcrystalline Be3BPO7 has a hexagonal system and contains the BO3 anionic group as its basic structural unit, which should play an important role for SHG coefficients. In fact, Be3BPO7 powder was found to have a significant SHG effect. INTRODUCTION When second harmonic generation (SHG) was detected by Franken and co-workers [1] in 1961 by passing a ruby laser beam through a quartz crystal, a great deal of activity in nonlinear optics was initiated. Since then, intensive research has been carried out in the field of nonlinear optical devices, as they are functional in the frequency range accessed by common laser sources. Nonlinear optical (NLO) materials are usually used to generate the requisite frequency and power for new laser sources that cannot be obtained directly from common laser sources. NLO materials have been playing an increasing, as well as an important, role both in laser science and technology. There has been a constant search for new and better NLO crystals in order to study and develop new laser sources and their practical applications over the past four decades. As a result of intensive studies, many excellent inorganic NLO crystals such as β-BaB2O4 (BBO) [2], LiB3O5 (LBO) [3], KTiOPO4 (KTP) [4], and KH2PO4 (KDP) [5] have been discovered. These crystals can be used for frequency conversion of Nd:YAG lasers from the visible to the UV range in many practical applications. The efficient frequency conversion of a NLO crystal depends on the field strength and frequency of the incident beam, effective NLO coefficients, refractive indices, and phase-matching properties of the crystal. As a general
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