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The optical transmission spectra, the photoluminescence (PL), and the photoluminescence excitation (PLE) spectra of the cobalt doped zinc oxide nanorods Zn1-xCoxO (x = 0.01, 0.10) were measured by Loan et al. [J. Phys. D: Appl. Phys. 42, 065412 (2009)] in the region 1.5-4 eV. These spectra exhibit a group of ultraviolet narrow lines in the region of 3.0-3.4 eV related to the near-band-edge emission of the host ZnO materials and a group of emission lines in the red region of 1.8-1.9 eV assigned to the radiative transitions within the tetrahedral Co2+ ions in the ZnO host crystal. The group of lines in the visible region provides important information about the electronic structure of the cobalt doped zinc oxide nanorods. This work investigates a theoretical crystal-field analysis of the visible lines associated to the Co2+ ion transition occupying a Td site symmetry in ZnO host crystal. A satisfactory correlations were obtained between experimental and calculated energy levels. The electronic structure was compared with the reported for cobalt transition ion doped in ZnO nanoparticles and bulk crystals [Volbers et al., Appl. Phys. A 88, 153 (2007) and H. J. Schulz and M. Thiede, Phys. Rev. B 35, 18 (1987)]. In order to explain the existence of excitation peaks observed near the band edge of the ZnO host, an energy transfer mechanism is proposed. [ABSTRACT FROM AUTHOR]

Abstract: The experimental studies have provided evidence of the occurrence of transitions from the 3T1g(3F) ground state to the crystal-field levels 3T2g(3F), 3T1g(3P) and 3A2g(3F) for the V3+ centres in Al2O3 crystal; and from the 3A2g(3F) ground state to the crystal-field levels 3T2g(3F), 3T1g(3F) and 3T1g(3P) for the Ni2+ centres in LiNbO3 crystal (levels are assigned to irreps of the Oh point symmetry group). Using the experimental spectroscopic data, theoretical calculations of the crystal-field levels of V3+:Al2O3 and Ni2+:LiNbO3 are carried out based on the Racah theory. The observed crystalline-field splittings of the V3+ and Ni2+ terms were accounted for using a C3 symmetry Hamiltonian. The spin–orbit interaction was taken into account in this work. The Racah, crystal-field and spin–orbit parameters, which fit experimental and theoretical energy levels, have been reliably obtained. A good agreement between the theoretical and experimental results for the energy levels of V3+:Al2O3 and Ni2+:LiNbO3 has been obtained. [Copyright &y& Elsevier]

Abstract: The polarized absorption spectra of vanadium(III) in Cs3VCl6·4H2O complex are presented in the UV–vis region and correspond to the transition from the ground state 3T1g(3F) to the excited states 3T2g(3F), 3T1g(3P) and 3A2g(3F). Semiempirical calculations of the crystal-field levels of the vanadium(III) with D 4h point group symmetry in Cs3VCl6·4H2O chromophore are carried out, leading to a good agreement between the theoretical and experimental energy levels. [Copyright &y& Elsevier]

The absorption and excitation spectra of the tetrahedrally coordinated Cr4+ ions doped in LiAlO2 oxide crystal were measured by Ku¨ck 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 Ku¨ck 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. [Copyright &y& Elsevier]