Sr2(OH)3NO3: the first nitrate as a deep UV nonlinear optical material with large SHG responses

Abstract

A noncentrosymmetric nitrate, Sr₂(OH)₃NO₃, has been obtained using a hydrothermal method. The structure is built up of nine coordinated SrO₃(OH)₆ polyhedra and triangular NO₃ groups. The SrO₃(OH)₆ polyhedra share their three equatorial oxygen atoms with three separate NO₃ groups to form SrO₃–NO₃ layers, and the layers are linked by the apical oxygen atoms in the third dimension. Owing to its special coordination, SrO₃(OH)₆ forces its three neighboring NO₃ groups to arrange into a perfect parallel alignment in the plane to give the maximum contribution to the nonlinear optical effect. Powder second-harmonic generation (SHG) using the Kurtz–Perry technique shows that Sr₂(OH)₃NO₃ is type I phase-matchable, and the measured SHG coefficient was 3.6 times that of KH₂PO₄. The result from the UV-vis diffuse reflectance spectroscopy study of the powder samples indicated that the short-wavelength absorption edge was below 200 nm, suggesting that Sr₂(OH)₃NO₃ is the first nitrate as a promising deep-UV nonlinear optical material.