I. N. Kurkin

Superhyperfine Structure in the EPR Spectra and Optical Spectra of Impurity f Ions in Dielectric Crystals: A Review

The results of observation and simulation of the superhyperfine (ligand hyperfine) structure (SHFS) of the electron paramagnetic resonance (EPR) spectra of rare-earth and uranium impurity ions in dielectric crystals have been systematized. The resolved SHFS of the EPR spectra of doped cubic crystals (with the fluorite and perovskite structures) has been observed for orientations of a constant magnetic field along the crystallographic axes. Most attention has been paid to tetragonal double fluorides LiRF4 (R = Y, Lu, Tm), in which the SHFS of the EPR spectra has also been found for intermediate orientations of the magnetic field. For the LiYF4: Nd3+ single crystal, the splitting of optical spectral lines due to the interaction of Nd3+ ions with nuclear magnetic moments of the nearest neighbor fluorine ions has been observed for the first time. The Van Vleck paramagnet LiTmF4: U3+ is characterized by the SHFS with clearly distinguishable components due to the interaction of uranium ions both with nuclei of the fluorine ions and with enhanced magnetic moments of the thulium nuclei. The SHFS envelopes of the EPR spectra of Yb3+, Ce3+, Nd3+, and U3+ ions in LiYF4 and LiLuF4 crystals are well reproduced by numerical calculations based on the microscopic model using only three fitting parameters: the width of transitions between the electron-nuclear sublevels of the complex containing the paramagnetic ion and nuclei of the ligands and two constants of covalent bonding of the f electrons with 2s and 2p electrons of the nearest neighbor fluorine ions.

Superhyperfine structure of the EPR spectra of impurity ions in the LiYF4 : Nd3+ system doped by 143Nd isotopes

Results of measuring the EPR spectra in the LiYF4: Nd3+ system doped by 143Nd isotopes with the nuclear spin I = 7/2 have been presented. We have succeeded to observe superhyperfine splitting of the EPR spectra of the samples under investigation at the orientation of the magnetic field B along the symmetry axis c of the crystal and at B ⊥ c on the lines corresponding to both even neodymium isotopes and 143Nd.

EPR of Gd3+ ion in mixed CeO2-Y2O3 nanocrystals

This paper reports on the results of EPR studies of mixed CeO2-Y2O3 crystals (including nanosized crystals) doped by gadolinium ions. It is revealed that the width of the line corresponding to the allowed transition 1/2 ↔ −1/2 between the Kramers-conjugated states |±1/2〉 of the Gd3+ ion decreases with a decrease in the powder size from macrosizes to nanosizes. The observed dependence can be due to the increase in the unit cell size during grinding of the samples.

Superhyperfine structure of the ESR spectra of Gd 3+ impurity ions in LiYF 4 double fluoride

Electron spin resonance spectra of Gd3+ ions forming a small (~0.0001 at %) impurity in a LiYF4 single crystal have been investigated in a wide temperature range from liquid helium to room temperature. A number of the fine-structure components of the spectrum exhibit a pronounced superhyperfine structure depending on the orientation of the external magnetic field with respect to the crystallographic axes. The superhyperfine structure was not observed in earlier ESR studies of double fluorides with a Gd3+ impurity.

EPR study of clusters of rare-earth ions in mixed fluoride crystals

The EPR spectra of the (BaF2)1 − x(CeF3)x system are studied for the concentrations x = 0, 0.001, 0.002, 0.005, 0.01, and 0.02. The appearance of new tetragonal centers is detected beginning from x = 0.002, the intensity of these centers being maximal at x = 0.01. The (CaF2)1 − x − y(CeF3)x(YF3)y double solutions with x = 0.001 and y from 0 to 0.02 are also studied. In addition to the ordinary tetragonal center, beginning from y = 0.001, a new tetragonal center appears with the same structure as in the previously studied mixed crystals based on BaF2—namely, the Ce3+-□-R3+ chain elongated along the fourfold axis substitutes the Ca2+-Ca2+-Ca2+ and Ba2+-Ba2+-Ba2+ chains in regular CaF2 and BaF2 crystals (□ is the cation vacancy, and R3+ is the Ce3+, La3+, or Y3+ trivalent ion).

Concentration dependence of EPR spectra in mixed (BaF2)1 − x(CeF3)x crystals

In the EPR spectra of the (BaF2)1 − x(CeF3)x system, additional lines appear as the concentration x in the mixture increases from 10−3 to 10−2, some of which correspond to tetragonal centers with g‖ = 0.725 and g⊥ = 2.52. These lines are similar to those detected previously in mixed (BaF2)1 − x − y(CeF3)x(LaF3)y systems with a low cerium concentration (x ≈ 10−3) and in the CaF2: Ce3+ crystal grown with added Na+ ions.

Superhyperfine Structure of the EPR Spectra of Nd 3+ Impurity Ions in Fluorite CaF 2

EPR spectra of a CaF2 single crystal that was grown from melt containing a small addition of NdF3 were studied. Signals corresponding to tetragonal centers of Nd3+ ions and cubic centers of Er3+ and Yb3+ ions were found. Superhyperfine structure (SHFS) in the spectra of the Nd3+ ions was observed for the first time in this crystal; parameters of the superhyperfine interaction of the Nd3+ ions with the nearest nine fluorine ions were determined. The dependence of the resolution of the Nd3+ EPR spectrum SHFS on the incident microwave power at the temperature of T ≈ 6 K was studied. Obtained results are discussed and compared with the literature data.