BaF₂TeF₂(OH)₂: A UV Nonlinear Optical Fluorotellurite Material Designed by Band-Gap Engineering

Balancing the wide band gap, large second harmonic generation (SHG) response, and moderate birefringence are significant but addressable challenges for designing nonlinear optical (NLO) materials. Based on the band-gap engineering in perovskite solar cell materials, we have successfully synthesized a new fluorotellurite, BaF₂TeF₂(OH)₂, which exhibits a pseudo-Aurivillius structure and crystallizes in a noncentrosymmetric and polar space group Pmn2₁. The physical property measurements show that this material can effectively balance the requirements among the short UV absorption edge (∼205 nm), large SHG response (∼3 × KDP) and moderate birefringence (∼0.078@350-700 nm) and is a promising ultraviolet NLO crystal.