EPR and optical absorption study of Cr3+-doped ammonium oxalate monohydrate single crystals

The electron paramagnetic resonance (EPR) study of the Cr3+-doped ammonium oxalate monohydrate (AOM) single crystal is done at room temperature. Two magnetically inequivalent sites for chromium are observed. The hyperfine structure for Cr53 isotope is also obtained. The spin Hamiltonian parameters are evaluated as: D=(309±2)×10−4 cm−1, E=(103±2)×10−4 cm−1, g=1.9820±0.0002, A=(161±2)×10−4 cm−1 for site I and D=(309±2)×10−4 cm−1, E=(103±2)×10−4 cm−1, g=1.9791±0.0002, A=(160±2)×10−4 cm−1 for site II, respectively. On the basis of EPR data the site symmetry of Cr3+ doped single crystal is discussed. 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 values of different parameters are B=803, C=3531, Dq=2208 cm−1, h=0.59 and k=0.21, where B and C are Racah parameters, Dq is crystal field parameter and h and k are nephelauxetic parameters, respectively.