EPR, optical absorption and superposition model study of Fe³(+) doped strontium nitrate single crystals

Electron paramagnetic resonance (EPR) study of Fe³(+) ions doped strontium nitrate (SN) single crystals is performed at liquid nitrogen temperature and at X band frequency. The spin Hamiltonian (SH) parameters are determined from the resonance lines observed at different angular rotations. The crystal field parameters (CFPs) are evaluated using superposition model of Newman. The Zeeman g-factor and zero-field splitting parameters (ZFSPs) of Fe³(+) ion in SN (truncated SH considered) are: g=1.9989 ± 0.002 and ∣D∣=(338 ± 5) × 10⁻⁴ cm⁻¹, ∣E∣=(10 ± 5)× 10⁻⁴ cm⁻¹, a=(458 ± 5)× 10⁻⁴ cm⁻¹, respectively. The Fe³(+) ion enters the lattice substitutionally replacing the Sr²(+) sites of cubic symmetry. The local site symmetry of Fe³(+) ion in the crystal is orthorhombic (lower than that of the host). The optical absorption study of the crystal is also done at room temperature in the wavelength range 195-925 nm. The energy values of different orbital levels are determined. The observed bands are assigned as transitions from the (6)A₁(g)(S) ground state to various excited states of Fe³(+) ion in a cubic crystal field approximation. The observed band positions are fitted with four parameters, the Racah interelectronic repulsion parameters (B and C), the cubic crystal field splitting parameter (Dq) and the Trees correction (α) yielding: B=934, C=2059, Dq=1450, and α=90 (in cm⁻¹). On the basis of EPR and optical data, the nature of metal-ligand bonding in this crystal is discussed. The ZFSPs are also determined theoretically using microscopic SH theory based on perturbation theory and CFPs, B(kq) obtained from superposition model. The values of ZFSPs thus obtained are ∣D∣=(340 ± 5) × 10⁻⁴ cm⁻¹ and ∣E∣=(15 ± 5) × 10⁻⁴ cm⁻¹.