Abstract :
The absorption and excitation spectra of the tetrahedrally coordinated Cr4+ ions doped in LiAlO2 oxide crystal were measured by Kück and Hartung at room temperature (Chem. Phys. 240 (1999) 387). These spectra have provided evidence of the occurrence of transitions from the 3A2(3F) ground state to the crystal-field split levels 3T2(3F), 3T1(3F) and 3T1(3P) (levels are assigned to the Td symmetry, i.e., ideal tetrahedron CrO4). The splitting of each band of the Td symmetry is due to the distortion of the ideal tetrahedron. Using the experimentally determined data from the absorption and excitation spectra, a theoretical calculation for the crystal-field levels of Cr4+:LiAlO2 was performed by Kück and Hartung, based on the angular overlap model theory. The calculation reveals a good agreement between the mean values of the bands, while it underestimates the splitting of each band. A detailed crystal-field analysis of electronic energy levels of Cr4+ doped in LiAlO2 oxide crystal based on the Racah theory is proposed in this work. The observed crystalline-field splitting of the Cr4+ terms was accounted for by using a C2 symmetric Hamiltonian. In turn, reliable crystal-field and Racah parameters have been obtained. This theoretical analysis confirms the observed crystalline-field splittings of the 3F and 3P terms of the Cr4+ ion doped in the oxide crystal LiAlO2.
