Prof. Grzegorz Leniec Profile

Prof. Grzegorz Leniec

at Szczecin Univ of Technology

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Publications (1)

Proceedings Article | 12 October 2005 Paper

EPR and optical properties of CaF2:Yb single crystals

G. Leniec, S. Kaczmarek, G. Boulon

Proceedings Volume 5958, 595825 (2005) https://doi.org/10.1117/12.622501

KEYWORDS: Ytterbium, Crystals, Ions, Absorption, Magnetism, Fluorine, Raman spectroscopy, Temperature metrology, Phonons, Ferromagnetics

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Electron paramagnetic resonance (EPR) measurements of CaF₂:Yb (5 mol. %) single crystals were performed for lattice sites substituted by Yb ions and also for the possibility of Yb³⁺ pairs arising. Among eight lines observed in the EPR spectrum, with g = 4.293, 4.1, 3.965, 3.665, 3.433, 3.13, 3.054, 2.894 we think mainly the lines coming from different isotopes of Yb³⁺ isolated ions of cubic symmetry one can distinguish: ¹⁷⁰Yb³⁺ I=0, ¹⁷¹Yb³⁺ I=1/2 and ¹⁷³Yb³⁺ I=5/2, but one can not exclude the lines coming from Yb³⁺ pairs. All of the lines have got an axial symmetry along the crystallographic axis, since the lines do not move with angular variation in the planes parallel and perpendicular to the axis. One can observe also the extra line in magnetic field orientation in every plane at 45°, with the B₀≈191 mT. The unidentified line corresponds to non-axial Yb³⁺ center or unknown impurity. The components of A and g tensors of the spin Hamiltonian for cubic symmetry were calculated. Temperature dependence of EPR lines shows agreement with the Curie law for most of the lines. Peak-to-peak linewidth changes continuously within 20 mT range for "as-grown" crystals, while shows distinct increase above 25 K for γ-irradiated ones. It suggests strong ferromagnetic coupling between neighbours Yb³⁺ and Yb²⁺ ions the latter being created due to Compton electron capture. So, Yb³⁺ co-exists with Yb²⁺ after the Yb³⁺-Yb²⁺ conversion under influence of γ-irradiation and/or annealing in hydrogen. It seems the Yb²⁺ centers arising in CaF₂:Yb (5 mol. %) single crystal after γ-irradiation are related to Yb³⁺, as an effect of recharging one of Yb³⁺ ion from a pair. Absorption measurements of CaF₂ highly doped with Yb³⁺ (0.5 mol. %, 5 mol. % and 30 mol. %) reveal the shifting of the IR maxima of 921 and 980 nm characteristic for 0.5 mol. % doping of Yb³⁺ towards the centrum of IR band (927 and 976 for 30 mol. % of Yb³⁺). Raman spectrum shows localized phonon centered at about 64 cm^-1 being confirmation of the Yb³⁺ pairs presence in the 5 mol. % of Yb³⁺ doped CaF₂ crystal.

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