Li7SrScB12O24 and Li7Ba0.6Ca0.4ScB12O24: two new quaternary rare-earth borates with short UV cutoff edges

Abstract

Two new quaternary rare-earth borates, Li₇M^IIScB₁₂O₂₄ (M^II = Sr, Ba_0.6Ca_0.4), crystallizing in the centrosymmetric space group R were synthesized by a high-temperature solution method and characterized. They are isostructural and exhibit a three-dimensional anionic [ScB₁₂O₂₄]⁹⁻ framework composed of B₆O₁₄ groups and ScO₆ octahedra with alkali- and alkaline-earth metal cations occupying the cavities and keeping the charge balance. The UV-Vis-NIR diffuse reflectance spectrum shows that the cutoff edge of Li₇SrScB₁₂O₂₄ is less than 200 nm, which indicates its potential application in the deep UV region. Li₇M^IIScB₁₂O₂₄ (M^II = Sr, Ba_0.6Ca_0.4) will become a new type of rare-earth borates that have a deep-UV cutoff edge (≤200 nm). Furthermore, infrared spectroscopy and thermal analysis were carried out and the results were analyzed.