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 6A1g(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, Bkq 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.

Angular variation of the EPR resonance line, M = +1/2 ↔ −1/2 in Fe3+:SN.52Research highlights► Fe3+:SN spin Hamiltonian parameters are determined from EPR resonance lines at 77 K. ► The crystal field parameters are evaluated using superposition model. ► The local site symmetry of Fe3+ ion in the crystal is orthorhombic. ► The optical absorption study of the crystal is also done at room temperature. ► Using EPR and optical data, the metal-ligand bonding in the crystal is discussed.