β-LaTeBO5 and RETeBO5 (RE = Y, Gd, Tb): Explorations of New Optical Materials in the RE(III)-Te(IV)-B-O System

Abstract

Exploring new materials and enhancing their optical properties is an endeavor of great significance. Combining different types of optical functional groups such as borate and tellurite anions into a same compound can produce new material with novel structure and enhanced optical performance. In the RE(III)-Te(IV)-B-O system, a borate tellurite, namely, β-LaTeBO₅ (β-LTBO) and a series of lanthanide borotellurites, namely, RETeBO₅ (RE = Y, Gd, Tb), have been successfully synthesized by using the high-temperature solution method. β-LTBO crystallizes in the space group of P2₁/c (No. 14) and its structure features [LaTeO₃]_∞ layers composed of La³⁺ cations and the [TeO₃]^2- anions, such layers are interconnected by the ¹[BO₂]_∞ chains consisting of [BO₃]^3- planer triangles into a novel 3D structure. RETeBO₅ (RE = Gd, Tb, Y) feature 0D [Te₂B₂O₁₀]^6- clusters in which a central [Te₂O₆]^4- dimer connects with two [BO₃]^3- groups on both sides of the dimer via Te-O-B bridges, and these 0D [Te₂B₂O₁₀]^6- clusters were interconnected by lanthanide ions to form the 3D structure. A phase transition from β phase to α phase was observed at 700 °C for LaTeBO₅ based on DSC and temperature dependent XRD studies. Excitingly, the birefringence of β-LTBO of 0.134@546 nm is much larger than those of RETeBO₅ (RE = Y, Gd) (0.08, 0.074@546 nm), which is the largest in the borate tellurite system. Theoretical calculations indicate that the ¹[BO₂]_∞ chains made a considerable contribution to the enhanced birefringence for β-LaTeBO₅. Furthermore, the luminescent and magnetic properties of RETeBO₅ (RE = Y, Gd, Tb) were also studied. The present study proposes that the investigation of the metal-Te(IV)-B-O system may potentially result in the identification of numerous novel multifunctional materials.