Correlation between NMR and nonlinear optical properties at boron sites in nonlinear optical β-BaB2O4 single crystals

To obtain detailed information about the nonlinear optical (NLO) properties of β-BaB2O4 crystals, the spin–lattice relaxation time T1 of 11B was measured. In addition, the T1 values for 11B in Li2B4O7, LiCsB6O10, LiB3O5, and BaB2O4 crystals were obtained. We analyzed the correlation between the parameters of the quadrupole interaction, the number of 3-coordinated borons, T1, and the NLO properties at the boron sites in these crystals. A correlation seems to exist between the asymmetry parameter of the 3-coordinated boron nucleus, the ratio of the number of 3-coordinated borons to the number of both 3-coordinated and 4-coordinated borons, and the NLO coefficient of each crystal, whereas the quadrupole coupling constant and T1 showed no correlation with the NLO coefficient.