EPR and optical absorption study of Cr3+-doped ammonium lithium sulphate single crystals

EPR study of Cr3+-doped ammonium lithium sulphate single crystals is carried out at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance line positions of different lines observed in the EPR spectra. The spin Hamiltonian parameters are found to be g=2.0003±0.0002, D=(269±2)×10−4 cm−1 and E=(82±2)×10−4 cm−1 for site I and g=1.9904±0.0002, D=(251±2)×10−4 cm−1 and E=(79±2)×10−4 cm−1 for site II, respectively. EPR data indicate that the site symmetry of Cr3+ ion in the crystal is distorted octahedron and it enters the lattice substitutionally replacing NH4+ sites and bind to the neighbouring extra Li+ vacancies necessary for charge compensation. From optical study, the energy values of different orbital levels are estimated. Further, the bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are obtained to be B=908, C=3553, Dq=1974 cm−1, h=0.052 and k=0.21.