0000000000541990
AUTHOR
N. Mironova
Near-infrared luminescence of isolated and exchange-coupled Ni2+ ions in NicMg1−cO solid solutions
NicMg1−cO (0.01 ⩽ c ⩽ 1) solid solutions were studied by near-infrared luminescence, optical absorption and X-ray absorption spectroscopies. It was found that Ni2+ ions form at c < 0.2 the exchange-coupled pairs, strongly bound via 90 ° super-exchange interactions, and are displaced at c ⩽ 0.6 to the ‘off-center’ positions. This explains the origin of the zero-phonon line splitting observed in the optical absorption and luminescence spectra. It was also found that the effective energy transfer from the single Ni2+ ions to the exchange-coupled Ni2+-Ni2+ pairs occurs at temperatures below 40 K.
X-ray absorption spectroscopy studies of the off-center Ni2+ions in Ni c Mg 1-c O solid solutions
In this work we present the x-ray absorption spectroscopy study of NicMg1-cO (0.01 <EQ c <EQ 1) solid solutions. The extended x-ray absorption fine structure (EXAFS) above the Ni K-edge was analyzed using the multi-shell fitting procedure. It was found that nickel ions are located in a distorted environment and shift upon dilution to the off- center positions. This fact follows from two main results: (1) in the first shell, the average Ni- O distance increases linearly upon dilution; (2) in the second shell, the average Ni-Ni distance remains unchanged and decreases slightly at low nickel concentration while the dependence of the Ni-Mg distance has a break at c approximately equals 0.6 and …
EXAFS and XANES Studies of CoxMg1−xO Solid Solutions Using a Laboratory EXAFS Spectrometer
Studies of the local electronic structure and the short-range order in solid solutions CoxMg1−xO with x varying from 0.02 to 1.00 are carried out on the CoK-edge X-ray absorption spectra using a laboratory EXAFS spectrometer. A non-monotonous change of the CoO distance in the first coordination shell with a bent at about x = 0.5 is established. The second coordination shell of cobalt is formed by cobalt and magnesium atoms with a distribution close to a statistical one. [Russian Text Ignored.]
Optical properties of natural topaz
The results of investigation of infrared, Raman and UV-Visible absorption spectra of natural topaz crystals from Ukraine before and after fast neutron irradiation are presented. We assume that the ~ 620 nm band in topaz crystals is associated with the presence of Cr 3+ , Fe 2+ and Mn 2+ impurities. The broad band with maxima at 650 cm -1 observed in Raman spectra for topaz irradiated by fast neutrons may be connected with lattice disorder. Exchange interaction between radiation defect and impurity ions during neutron irradiation leads to appearance of additional absorption band in UV-VIS spectra and bands broadening in infrared and Raman spectra of investigated crystals.
Studies of CoxMg1-xO Solid Solutions Using Laboratory EXAFS-Spectrometer
Studies of the local electronic structure and the short-range order in solid solutions Co x Mg1-x O with x equal from 0.02 to 1.00 have been carried out on the Co K-edge X-ray absorption spectra measured using the laboratory EXAFS-spectrometer. A non-monotonous change of the Co-O distance in the first coordination shell with the bent at x=0.5 has been established. The second coordination shell of cobalt has been formed by cobalt and magnesium atoms with a distribution close to statistical.
Low Temperature Optical Absorption by Magnons in KNiF3 and NiO Single-Crystals
Optical absorption spectra of KNiF3 and NiO stoichiometric single-crystals were measured at 5 K in the range from 4000 to 50000 cm-1. The observed bands are interpreted based on the energy levels diagram for Ni2+ (3d 8 ) ion in a cubic crystal field. The crystal-field parameter Dq is equal to 766 cm-1 in KNiF3 and 890 cm-1 in NiO. Particular attention is paid to the band due to the magnetic-dipole 3A2g(F)→3T2g(F) transition, located at 7700 cm-1 in KNiF3 and at 8900 cm-1 in NiO. We show that the energy difference between the two peaks, located at the low energy side of the band, is related to the zone-center (k=0) one-magnon energy, so that the low-energy peak is attributed to the pure exci…