Theoretical study of spin singlets contributions to zero-field splitting and local lattice structure of Cr2+ in CdGa2S4

A theoretical method for investigating the inter-relation between electronic and the molecular structures of a d4 ion in a tetragonal ligand-field has been established on the basis of 210 x 210 complete energy matrix within a weak-field-representation. Using the method, the local structure parameters of CdGa2S4:Cr2+ system are determined by the experimental EPR zero-field splitting (ZFS) spectra. Our results show that the local structure around Cr2+ is a compression distortion and the local lattice structure parameters R = 2.46 A and θ = 57.63 deg. are determined. Moreover, the contributions of the spin singlets to ZFS parameters of Cr2+ ions in CdGa2S4 crystals are investigated for the first time. The results indicate that the spin singlets contributions to ZFS parameter D are negligible, but the contributions to ZFS parameters a and F cannot be neglected.