RbNa(HC3N3O3)•2H2O exhibiting a strong second harmonic generation response and large birefringence as a new potential UV nonlinear optical material

A new mixed alkali hydro-isocyanurate, RbNa(HC3N3O3)center dot 2H(2)O, with the noncentrosymmetric space group Pna2(1) (No. 33), has been successfully grown by a hydrothermal method. The structure can be described as 2D wavy [Na(HC3N3O3)O-4](infinity) layers separated by Rb atoms. The UV-vis diffuse reflection measurement revealed that RbNa(HC3N3O3)center dot 2H(2)O has a large band gap of 5.10 eV, corresponding to the UV cutoff edge of 241 nm. The polarizing microscope measurement of a micron-sized single crystal shows that RbNa(HC3N3O3)center dot 2H(2)O has a large birefringence of 0.194. The powder SHG measurement indicated that RbNa(HC3N3O3)center dot 2H(2)O exhibits a strong SHG effect that is 5.3 times that of KH2PO4 (KDP) and can realize phase-matching in the visible and UV region. Moreover, the differences in the SHG responses between RbNa(HC3N3O3)center dot 2H(2)O and two isostructural compounds have been investigated, which depend heavily on the structural modulation of the (HC3N3O3)(2-) group by cations. Meanwhile, the electronic structures and optical properties were well analyzed using DFT methods.