An Empirical Relationship between Optical Properties and the Nuclear Quadrupole Coupling Parameters in the Boron Sites in the Nonlinear Optical CsLiB₆O₁₀

Abstract

The rotation patterns of the nuclear magnetic resonance of ¹¹B (I=3⁄2) in a nonlinear optical CsLiB₆O₁₀ single crystal were measured in three mutually perpendicular crystal planes. We observed sixteen different spectra which could be divided into two groups corresponding to two kinds of boron atoms, B(1) and B(2), having different boron–oxygen rings and lying at crystallographically inequivalent sites. From these results, the quadrupole coupling constants and the asymmetry parameters were determined at room temperature for the first time. For the 4-coordinated B(1), e²qQ⁄h=0.23±0.03 MHz and η=0.456±0.004, and for the 3-coordinated B(2), e²qQ⁄h=2.58±0.03 MHz and η=0.276±0.004. The directions of the principal axes of the electric field gradient tensors were also determined. The spectra for the two groups have different principal values of the electric field gradient tensor and originate from magnetically inequivalent sites. The principal Z-axis of the EFG tensor nearly coincides with the normal to the plane of the boron–oxygen triangle. We found an interesting correlation between the asymmetry parameter and the largest nonlinear optical coefficient.