LiASi2O5 (A = K, Rb): Effects of cations on crystal structure and optical properties

Abstract

Tetrahedral basic building units are important for the design of new nonlinear optical materials. In this paper, two alkali metal silicates have been reported to have differentiated symmetry and optical properties. LiKSi2O5 crystallizes in the monoclinic system of P21 with the ultraviolet cutoff of 255 nm; LiRbSi2O5 crystallizes in the orthorhombic system of Pca21 with the ultraviolet cutoff of 240 nm. The calculation results show that the second harmonic generation coefficients and the wavelengths of phase matching for LiKSi2O5 are d16 = 0.30 pm/V and 585 nm, while that for LiRbSi2O5 are d24 = 0.38 pm/V and 446 nm, respectively. Hence, the different radii of cations lead to different coordination environments, which will affect the connection styles further influences the symmetries and optical properties of the compounds. It is confirmed that simple ion substitution can change the optical properties, which provides a feasible way for the modulation of nonlinear optical property.