Optical and Magnetic Properties of Cu-Containing Borates with “Antizeolite” Structure

Crystals of copper-doped barium fluoride borate solid solutions Ba3(BO3)2–xF3x:Cu were grown from high-temperature solution. Using X-ray single-crystal diffraction, the structure was solved and refined in Pbam space group. These crystals are colored in brown, revealing linear dichroism. Optical and electron spin resonance spectroscopic investigations concluded that the light absorption of Ba3(BO3)2–xF3x:Cu crystals is caused by both the exciton and free charge carriers. This phenomenon is similar to those observed in other colored “antizeolites” built with the positively charged framework of porous [Ba12(BO3)6]6+ building blocks (hence named as antizeolites). The coloring of Ba3(BO3)2–xF3x:Cu crystals is associated with the absorption of Cu2+ ions as well. For the first time, constants of the hyperfine interaction of copper ions Cu2+ in octahedral fluorine surroundings [CuF6]4– have been determined.