Nonlinear optical properties of borate crystals

We have studied the effect of different chemical bonding structures of boron atoms on the second-order nonlinear optical behavior of borate crystals from the chemical bond viewpoint. Several typical borate crystals, including LiB3O5, β-BaB2O4, BiB3O6, NdAl3(BO3)4, Ca4LnO(BO3)3, K[B5O6(OH)4]·2H2O, Eu2B5O9Cl and Ca2B5O9Br, with different chemical bonding structures of boron atoms are investigated. The results show that the different chemical bonding structures of boron atoms have a strong effect on the second-order nonlinear optical behavior of borate crystals. Further, the calculated values show that forming B–O rings would decrease the NLO response of borate crystals and that [BO3]3− groups possess larger nonlinear optical contributions than [BO4]5− groups.