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.