LaBS3 revisited: a promising mid-infrared nonlinear optical material

Thioborates are considered new potential mid-infrared nonlinear optical (NLO) crystals with wide band gaps and large second-harmonic generation (SHG) coefficients. Despite the fact that many rare-earth thioborates are structurally non-centrosymmetric, their SHG properties have only been studied very recently and their mid-infrared (Mid-IR) nonlinear optical properties have not yet been studied. In this work, we provide a new synthetic route for LaBS3 (LBS) by solid state reactions of La2S3, B and S with Li2S as flux, and we further study its thermal and optical properties, and theoretically explore the origin of its IR nonlinear optical properties by DFT calculations. Remarkably, LBS possesses balanced properties required for a good Mid-IR NLO crystal, a large SHG effect (1.2 x AgGaS2@2.05 mu m - the largest among all known ortho-thioborates), a high laser induced-damage threshold (14 times of AgGaS2), a wide band gap (3.18 eV), a wide infrared transmission range (0.35-25 mu m) and high thermal stability. Theoretical calculations suggest that its large SHG effect originates from the synergy effects of the pi-conjugated [BS3](3-) anions (41.82%) and the [LaS9](15-) groups (58.18%).

Automated summary

Researchers report a new synthetic route to prepare LaBS3, a crystal with excellent mid-infrared nonlinear optical properties. The experimental results show that LaBS3 exhibits a large second-harmonic generation effect, high laser induced-damage threshold, wide band gap, wide infrared transmission range, and high thermal stability. Theoretical calculations suggest that the large second-harmonic generation effect of this material originates from the synergy effects of the pi-conjugated [BS3](3-) anions and [LaS9](15-) groups.