Li3AlSiO5: the first aluminosilicate as a potential deep-ultraviolet nonlinear optical crystal with the quaternary diamond-like structure

Abstract

Deep-ultraviolet (deep-UV) nonlinear optical (NLO) crystals play a crucial role in modern laser frequency conversion technology. Traditionally, the exploration of deep-UV NLO crystals is mainly focused on borates, while, the use of phosphates recently opened up a novel and promising non-boron pathway for designing new deep-UV NLO crystals. Extending this pathway to aluminosilicates led to the discovery of Li₃AlSiO₅, the first NLO crystal in this system. It crystallizes in the polar space group Pna2₁ (no. 33) with a quaternary diamond-like structure composed of LiO₄, AlO₄ and SiO₄ tetrahedral groups. The compound exhibits a deep-UV cut-off edge below 190 nm and is phase matchable with moderate powder second harmonic generation (SHG) intensity (0.8KH₂PO₄). The band gap calculated using PBE0 is 7.29 eV, indicating that the cut-off edge of the Li₃AlSiO₅ crystal can be down to 170 nm. In addition, the compound is nonhygroscopic and thermally stable up to ∼1472 K. These results suggest that Li₃AlSiO₅ is a potential deep-UV NLO crystal. First-principles studies were performed to elucidate the structure–property relationship of Li₃AlSiO₅.