Growth, Structure and Optical Characterization of Rb(3)Ti(3)P(5)O(20) Single Crystal

Phosphate crystals attract much attention on account of their rich crystal structures and excellent physical and chemical properties. Herein, Rb(3)Ti(3)P(5)O(20) single crystals were grown by the high temperature solution method using Rb(2)CO(3) and NH(4)H(2)PO(4) as the fluxes. This crystal, with non-centrosymmetric Pca2(1) space group, presents a three-dimensional framework structure composed of [TiO(6)] octahedron, [PO(4)] tetrahedra, and [P(2)O(7)] dimers. The electronic structure was measured via X-ray photoelectron spectroscopy. The measurements found that Rb(3)Ti(3)P(5)O(20) has stronger Ti–O ionic bonding properties and weaker P–O covalent bonding properties compared to RbTiOPO(4). Optical measurements indicated that Rb(3)Ti(3)P(5)O(20) has a 3.54 eV band gap and a wide transmission range (0.33–4.5 μm). Theoretical calculations showed that Rb(3)Ti(3)P(5)O(20) crystals have a moderate birefringence of 0.079 at 1064 nm. In addition, the relationship of the structure–property was studied using first-principles method. The results demonstrated that TiO(6) octahedron played a significant role for the optical properties.