Second Harmonic Generation in β-K₂TeW₃O₁₂: An Acentric Crystal Designed from Centric Phase via Pressure Modulation

The latent value of nonlinear optical (NLO) crystals applied in solid-state laser equipment necessitates the development of applicable strategies for constructing noncentrosymmetric (NCS) crystals. By modulating the synthetic temperature and pressure to achieve the rearrangement of [TeO₃]^2- groups, a new NCS tellurium tungstate, β-K₂TeW₃O₁₂ (β-KTW), with a strong second harmonic generation (SHG) response was synthesized based on its centrosymmetric polymorphic phase α-K₂TeW₃O₁₂ (α-KTW). Computational calculation reveals that the large SHG response of β-KTW (15 × KH₂PO₄@1064 and 1.5 × KTiOPO₄@1950 nm) could be attributed to the uniform arrangement of the NLO-active [TeO₃]^2- and [WO₆]^6- groups. β-KTW also exhibits enlarged birefringence (0.196@1064 nm) and a high laser damage threshold (42.3 MW cm^-2), showing great potential as a nonlinear crystalline material. This work also provides a new route for the construction of NLO crystals based on centric structure, i.e., reverse pressure regulation.