β-BaGa4Se7: a promising IR nonlinear optical crystal designed by predictable structural rearrangement

Abstract

Rationally designing new inorganic materials with specific functional properties is a fascinating challenge. This is particularly true with the nonlinear optical (NLO) crystals, which can expand the spectral ranges of solid-state lasers from ultraviolet (UV) to infrared (IR) through a second harmonic generation (SHG) or optical parametric oscillation (OPO) process. Herein, a high-performance IR NLO crystal, β-BaGa₄Se₇, has been successfully predicted and synthesized by the optimal rearrangement of the NLO-active basic structure units. The stability and functional properties of the material were simulated by first-principles calculations, and eventually it was also successfully synthesized via a high-temperature solid-state reaction in a sealed silica tube. More importantly, this material can exhibit exceedingly excellent NLO properties, including strong SHG response (5 × AgGaS₂), wide transmission range (0.44–20 μm) and high laser damage threshold (680 MW cm⁻², 20 × AgGaS₂), as well as stable physicochemical properties. These indicate that β-BaGa₄Se₇ is a promising IR NLO crystal. The discovery of β-BaGa₄Se₇ can also provide new insights into the rational design of IR NLO crystals based on the predictable structural rearrangement.