M2Al2Ti(PO4)4 (M = Rb, Cs): Synthesis and Optical Property Investigation of Two Titanium Phosphates with Dissimilar Structural Configuration

Abstract

Inorganic transition metal phosphates are favored materials for various optoelectronic fields such as photoluminescence, optical catalysis, and nonlinear optics, and further exploration of new transition metal phosphates and studying the impact of transition metal atoms on the structure and properties of the compound is a persistent scientific concern. Herein, two new Ti-containing open framework aluminum phosphates, M2Al2Ti(PO4)4 (M = Rb, Cs) were synthesized through a high-temperature flux method. Both structures are orthophosphates containing isolated PO4, AlO4, and TiO6, yet they exhibit dissimilar overall structural configurations. Rb2Al2Ti(PO4)4 features one-dimensional (1D) [Al-P-O]∞ chains which are further bridged by TiO6 to form 2D layers. Whereas, Cs2Al2Ti(PO4)4 displays 2D [Al-P-O]∞ layers, which are further bridged by TiO6 to form a 3D network with large channels. In addition, detailed experimental characterizations and theoretical computations were carried out; both compounds exhibit UV cutoff edges down to 300 nm based on the UV-vis diffuse reflectance test. Based on calculations Cs2Al2Ti(PO4)4 has a birefringence Δn = 0.033 at 1064 nm.