EPR, Optical Absorption and Superposition Model Study of Fe3+-Doped Ammonium Dihydrogen Phosphate Single Crystals

X-band electron paramagnetic resonance (EPR) studies are carried out on Fe3+ ions doped in ammonium dihydrogen phosphate (ADP) single crystals at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations. The obtained values of spin Hamiltonian and zero-field parameters of the Fe3+ ion in ADP are: g = 1.994 +/- A 0.002, |D| = (220 +/- A 5) x 10(-4) cm(-1) and a = (640 +/- A 5) x 10(-4) cm(-1). On the basis of EPR data, the site symmetry of the Fe3+ ion in the crystal is discussed. The Fe3+ ion enters the lattice substitutionally replacing the NH4 (+) sites. The optical absorption of the crystal is also studied at room temperature in the wavelength range of 195-925 nm. The energy values of different orbital levels are calculated. The observed bands are assigned as transitions from the (6) A (1g) (S) ground state to various excited quartet levels of the Fe3+ ion in a cubic crystalline field. From the observed band positions, Racah interelectronic repulsion parameters (B and C), cubic crystal field splitting parameter (D (q) ) and Trees correction are calculated. There values are: B = 970, C = 1,923, D (q) = 1,380 cm(-1) and alpha = 90 cm(-1), respectively. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The zero-field splitting (ZFS) parameters are also determined theoretically using B (kq) parameters estimated from the superposition model. The values of ZFS parameters thus obtained are |D| = (213 +/- A 5) x 10(-4) cm(-1) and |E| = (21 +/- A 5) x 10(-4) cm(-1).