High-resolution optical study of Ho3+Ho3+ pairs in LiY1−xHoxF4 crystals

High-resolution spectra of holmium-doped LiYF4 crystals at low temperatures were investigated. It was shown that weak lines observed near some main lines in the spectra belong to the Ho3+Ho3+ pair centers. These satellites can be explained by two types of pairs with the magnetic dipole coupling within each of them, provided that a change of the crystal field due to lattice distortion is taken into account.