Crystal-field splitting of the Cr 4+ terms in LiAlO 2 oxide crystal

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The absorption and excitation spectra of the tetrahedrally coordinated Cr 4+ ions doped in LiAlO 2 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 3 A 2( 3 F) ground state to the crystal-field split levels 3 T 2( 3 F), 3 T 1( 3 F) and 3 T 1( 3 P) (levels are assigned to the T d symmetry, i.e., ideal tetrahedron CrO 4). The splitting of each band of the T d 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 Cr 4+:LiAlO 2 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 Cr 4+ doped in LiAlO 2 oxide crystal based on the Racah theory is proposed in this work. The observed crystalline-field splitting of the Cr 4+ terms was accounted for by using a C 2 symmetric Hamiltonian. In turn, reliable crystal-field and Racah parameters have been obtained. This theoretical analysis confirms the observed crystalline-field splittings of the 3 F and 3 P terms of the Cr 4+ ion doped in the oxide crystal LiAlO 2.