Linear and nonlinear optical properties of Na3La2(BO3)3 crystal

A 30×20×8 mm3 Na3La2(BO3)3 crystal has been grown by the top-seeded solution growth method (TSSG) using Na2O-B2O3-NaF as flux. The refractive indices at thirteen wavelengths from 0.2537 to 2.325 μm were accurately measured by the minimum deviation method, and the Sellmeier equations were accordingly constructed. The nonlinear optical (NLO) coefficients were measured by the Maker fringe method, which gave results of d31=1.45 pm/V, d32=0.67 pm/V, and d33=−1.06 pm/V, respectively. For second-harmonic generation (SHG) of 1064 nm, the effective NLO coefficient (deff) of type I phase-matching reaches the maximum value (1.44 pm/V) at the phase-matching angles θ=77.0°, ϕ=212.1°, which is larger than that of LiB3O5 (LBO). First-principle calculations suggest that Na3La2(BO3)3 possesses two types of NLO-active atom groups, BO3 group with π-orbital system and La-centered polyhedron with large polar displacement, of which the latter could be considered as a new type of NLO-active atom group.