Studies of the optical and EPR spectral data for the trigonal strong field Cr3+ centers in Cr3+-doped Ca3Ga2Ge4O14 and Sr3Ga2Ge4O14 crystals

This paper represents the unified theoretical computations for the trigonal strong field Cr3+ centers (assigned to Cr3+ at octahedral Ga3+ sites) in Cr3+-doped Ca3Ga2Ge4O14 and Sr3Ga2Ge4O14 crystals. The computations adopt the complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model where the contributions from both the spin-orbit parameter of central dn ion (in the classical crystal field theory) and that of ligand ion are contained. The calculated six optical bands and three spin-Hamiltonian parameters (g factors g//, g⊥ and zero-field splitting D) with only three adjustable parameters are reasonably coincident with the observed values. The very small local lattice relaxation in the Cr3+ centers in both crystals indicates the similarities of valence and ionic radius between Cr3+ ion and the replaced host ion. This supports the assignment that the trigonal strong field Cr3+ centers in both crystals are due to Cr3+ at octahedral Ga3+ site rather than octahedral Ge4+ site (the latter may be the weak field Cr3+ center).