Single crystal EPR, optical absorption and superposition model study of Cr3+ doped ammonium dihydrogen phosphate

The electron paramagnetic resonance (EPR) studies are carried out on Cr3+ ion doped ammonium dihydrogen phosphate (ADP) single crystals at room temperature. Four magnetically inequivalent sites for chromium are observed. No hyperfine structure is obtained. The crystal-field and spin Hamiltonian parameters are calculated from the resonance lines obtained at different angular rotations. The zero field and spin Hamiltonian parameters of Cr3+ ion in ADP are calculated as: |D| = (257 ± 2) × 10−4 cm−1, |E| = (79 ± 2) × 10−4 cm−1, g = 1.9724 ± 0.0002 for site I; |D| = (257 ± 2) × 10−4 cm−1, |E| = (77 ± 2) × 10−4 cm−1, g = 1.9727 ± 0.0002 for site II; |D| = (259 ± 2) × 10−4 cm−1, |E| = (78 ± 2) × 10−4 cm−1, g = 1.9733 ± 0.0002 for site III; |D| = (259 ± 2) × 10−4 cm−1, |E| = (77 ± 2) × 10−4 cm−1, g = 1.973 ± 0.0002 for site IV, respectively. The site symmetry of Cr3+ doped single crystal is discussed on the basis of EPR data. The Cr3+ ion enters the lattice substitutionally replacing the NH4+ sites. The optical absorption spectra are recorded in 195–925 nm wavelength range at room temperature. The energy values of different orbital levels are determined. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The calculated values of Racah interelectronic repulsion parameters (B and C), cubic crystal-field splitting parameter (Dq) and nephelauxetic parameters (h and k) are: B = 640, C = 3070, Dq = 2067 cm−1, h = 1.44 and k = 0.21, respectively. ZFS parameters are also determined using Bkq parameters from superposition model.