Sr-2(OH)(3)NO3: the first nitrate as a deep UV nonlinear optical material with large SHG responses

A noncentrosymmetric nitrate, Sr-2(OH)(3)NO3, 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 Sr-2(OH)(3)NO3 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 Sr-2(OH)(3)NO3 is the first nitrate as a promising deep-UV nonlinear optical material.