EPR and optical absorption study of Mn2+-doped zinc ammonium phosphate hexahydrate single crystals

EPR study of Mn2+-doped zinc ammonium phosphate hexahydrate (ZAPH) is done at room temperature. The Mn2+ spin Hamiltonian parameters are evaluated employing a large number of resonant line positions observed for different orientations of the external magnetic field. The evaluated value of g-factor is 1.9527±0.0002 and the values of other parameters D, E, a, A and B (in 10−4 cm−1) are, 175±2, 58±2, 10±1, 92±2 and 86±2, respectively. The optical absorption study of the crystal is also done. The observed bands are assigned as transitions from the 6A1g(S) ground state to various excited quartet levels of Mn2+ ion in a cubic crystal field. These bands are fitted with four parameters: inter-electronic repulsion parameters (B and C), cubic crystal field splitting parameter (Dq), and Tree's correction (α). The values obtained for the parameters are B=917, C=2254, Dq=756 and α=76 cm−1. From the data obtained the surrounding crystal field and the nature of metal-ligand bonding are discussed. The considerable decrease in the values of B and C from their free ion values indicates the existence of a fair amount of covalent bonding between the central metal ion and the ligand. On the basis of the deviations Δg=g−2.0023, the transfer of electrons to or from the central metal ion for bond formation is ascertained.