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Electron Paramagnetic Resonance (EPR) and Raman Spectroscopy were used to study the low temperature phase transition of pulled Li 3 ThF 7 single crystals, occurring at 281 K. In both cases, the room temperature spectra were very broad, owing to the statistical disorder and high ionic mobility of the lithium ions, which occupy only 3/4 of their structural sites. The results are compatible with a first order ferroelastic transition from the room temperature orthorhombic D 2h 22 phase to a monoclinic C 2h (x) one. The symmetry rules are well respected assuming a model with four lithium ions in average per chemical formula. The EPR spectra show also the appearing of additional ferroelastic domains.

Cerium doped fluoride materials are known for their fast scintillating properties. Large LuF3 single crystals have been grown by the Czochralski method. Electron paramagnetic resonance (EPR) has been used to characterize Ce3+ and residual paramagnetic impurities. At 300 K Gd3+ has been detected, which substitutes for Lu3+ in LuF3. From the analysis of the EPR angular dependence the b 2 0 parameter for Gd3+ was determined to be 1.846 GHz, which is about times larger than the corresponding parameter in LaF3 hosts structure. At 10 K the EPR spectra show the presence of Ce3+ and other still undetermined rare earth impurities. The analysis of the EPR angular dependence of Ce3+ shows a strong nearly axial symmetry of the g tensor with g xx = 0.29, g yy = 0.60 and gzz = 3.374. The Y axis of the g tensor is parallel to the crystallographic b direction, whereas the X and Z axes are rotated in the ac plane by 25°.

Gadolinium (Gd3+) in Czochralski-grown lutetium fluoride (LuF3) has been investigated by electron paramagnetic resonance (EPR). Detailed analysis of the EPR angular dependencies reveals that Gd3+ entered substitutionally for Lu3+ in monoclinic Cs site symmetry. The Lu site seems to be more distorted by the Gd ion as compared to the Y site in YF3. The zero-field splitting of the ground state b20 is −1.8372 GHz which is more than twice compared to that of Gd3+ in host crystals of LaF3, in which gadolinium has the same co-ordination number. The results of the fine structure analysis are compared to a similar study in the iso-structural host YF3. The obtained results seem to be in contrast to the superposition model.

Single crystals of YF3 grown by the Czochralski method have been investigated by electron paramagnetic resonance (EPR). In this paper we present an EPR analysis of residual Gd3+ impurities. We found that the Gd3+ rare-earth ion substitutes for Y3+ in YF3. Detailed analysis of the EPR spectra allowed us to determine the fine structure parameters of Gd3+ in monoclinic Cs site symmetry. The EPR angular dependence is dominated by the electronic quadrupole tensor; the g-factor is slightly axial. The b02 parameter found for Gd3+ in YF3 is unexpectedly high when compared to Gd3+ in the hosts of LaF3 structure where the coordination number is the same. The results let us conclude that YF3 is a promising laser host crystal.

Single crystals of monohydrated $L$-asparagine have been grown from aqueous solutions using $\mathrm{Mn}{\mathrm{Cl}}_{2}$ as doping material. Electron paramagnetic resonance (EPR) was used to determine the incorporation sites of ${\mathrm{Mn}}^{2+}$ ions in the crystal structure. Depending on small $p\mathrm{H}$ changes and crystal growth kinetics in the aqueous solutions, ${\mathrm{Mn}}^{2+}$ ions are incorporated in two chemically distinct sites in asparagine crystals. The first shows isotropic six-line hyperfine-split EPR spectra, whereas the second shows anisotropic multiple line splitting due to ${\mathrm{Mn}}^{2+}$ fine structure $(S=5∕2)$ and hyperfine interaction $(I=5∕2)$. Angular dependencies of the ${\mathrm{Mn}}^{2+}$ EPR spectra in three mutually perpendicular crystal planes were measured and analyzed. The results are discussed in terms of the metal incorporation site symmetry in the crystal structure of monohydrated $L$-asparagine.