Magnetically ordered multinary semiconductors

The exchange charge model of crystal field theory has been used to analyze systematically the ground state absorption spectra of octahedrally coordinated Ni 2+ ion in isostructural nickel halide crystals NiCl 2 , NiBr 2 , and NiI 2 . The parameters of the crystal field acting on the Ni 2+ ion are calculated from the available crystal structure data. The obtained energy level schemes are compared with experimental absorption spectra; a good agreement with experimental data is demonstrated. Dependencies of the crystal field invariants and covalence effects on the type of ligands are considered. It is shown numerically that the overlap effects between Ni 2+ ion and ligands increase with an increase of the ligands’ atomic number resulting in the following order of the degree of covalence: NiI 2 >NiBr 2 >NiCl 2 .

Comparative crystal field study of Ni2+ energy levels in NiCl2, NiBr2, and NiI2 crystals

Comparative study of crystal field effects for Ni2+ ion in LiGa5O8, MgF2 and AgCl crystals

Photoluminescence of Ga2S3 and Ga2S3: Mn single crystals

Systematic ab initio calculations of the ground-state absorption spectra and covalence effects in three isostructural anisotropic crystals with layered structure (NiCl2, NiBr2 and NiI2) are presented. The recently developed first-principles approach to the analysis of the absorption spectra based on the discrete variational multi-electron method (K. Ogasawara et al., Phys. Rev. B 64 (2001) 115413) was used in the calculations. The method is based on the numerical solution of the Dirac equation; no phenomenological parameters are used in the calculations. As a result, energies of the Ni2+-ion multiplets and absorption spectra of all above-mentioned crystals were calculated, assigned and compared with experimental spectra. By performing analysis of the molecular orbital population, it was shown that the degree of covalence of the chemical bond between Ni2+ ion and ligands is in the following order: NiI2>NiBr2>NiCl2.

Comparative first-principles study of the Ni2+ absorption spectra and covalence effects in isostructural crystals NiCl2, NiBr2 and NiI2

Single crystals of ZnGa2S4:Mn2+ and ZnGa2S4:Ni2+ were grown by chemical vapor deposition technique. The absorption spectra of these crystals were measured in the wavelength region of 400–3000 nm at 298 K. The optical energy gap is found to be 3.25 eV for the ZnGa2S4, 3.21 eV for the ZnGa2S4:Mn2+ and 3.15 eV for the ZnGa2S4:Ni2+ crystals. Three absorption peaks were observed at 2.30 eV, 2.55 eV and 2.66 eV for the ZnGa2S4:Mn2+ and assigned as, 6A1→4E, 6A1→4T2 and 6A1→4T1 transitions of Mn2+ at Td crystal field. The absorption peaks of ZnGa2S4:Ni2+ were observed at 0.54 eV, 1.14 eV, 1.50 eV, 1.76 eV, 1.94 eV and 2.25 eV. These absorption transitions were assigned as, \varGamma1→\varGamma3+\varGamma4, \varGamma1→\varGamma5, \varGamma1→\varGamma3+\varGamma4, \varGamma1→\varGamma5, \varGamma1→\varGamma4 and \varGamma1→\varGamma3, respectively using Td crystal field along with the 1st order spin-orbit coupling effect.

Seung-Ho Cheon

Papers

Optical Absorption of ZnGa2S4:Ni2+ and ZnGa2Mn2+ Single Crystals

Impurity optical absorption spectra of ZnGa2Se4:Ni2+ single crystals