Growth and EPR and optical properties of Li2B4O7 single crystals doped with Co2+ ions

Li2B4O7 single crystals doped with Co ions were grown by the Czochralski method. The electron paramagnetic resonance (EPR) and optical absorption spectra of Li2B4O7 (LBO) single crystals doped with Co2+ ions were measured. The EPR spectra could be described by the spin-Hamiltonian with an effective spin of S=12 in octahedral symmetry. The values of g and A tensors and direction cosines characterizing Co2+ centers in the LBO crystal were determined for the first time also. The EPR data reveals at least two types of Co2+ centers. Optical absorption was measured in the range of 200 to 3200 nm for “as-grown” and γ-irradiated samples of Co:Li2B4O7 crystals confirming octahedral coordination of Co2+ ions and cation vacancies arising in the “as-grown” crystal.